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Pendyala, Raghu Kishore. "Automated Simulation of Organic Photovoltaic Solar Cells." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15338.
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This project is an extension of a pre-existing simulation program (‘Simulation_2dioden’). This simulation program was first developed in Konarka Technologies. The main purpose of the project ‘Simulation_2dioden’ is to calibrate the values of different parameters like, Shunt resistance, Series resistance, Ideality factor, Diode current, epsilon, tau, contact probability, AbsCT, intensity, etc; This is one of the curve fitting procedure’s. This calibration is done by using different equations. Diode equation is one of the main equation’s used in calculating different currents and voltages, from the values generated by diode equation all the other parameters are calculated.
The reason for designing this simulation_2dioden is to calculate the values of different parameters of a device and the researcher would know which parameter effects more in the device efficiency, accordingly they change the composition of the materials used in the device to acquire a better efficiency. The platform used to design this project is ‘Microsoft Excel’, and the tool used to design the program is ‘Visual basics’. The program could be otherwise called as a ‘Virtual Solar cell’. The whole Virtual Solar cell is programmed in a single excel sheet.
An Automated working solution is suggested which could save a lot of time for the researchers, which is the main aim of this project. To calibrate the parameter values, one has to load the J-V characteristics and simulate the program by just clicking one button. And the parameters extracted by using this automated simulation are Parallel resistance, Series resistance, Diode ideality, Saturation current, Contact properties, and Charge carrier mobility.
Finally, a basic working solution has been initiated by automating the simulation program for calibrating the parameter values.
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Pachoumi, Olympia. "Metal oxide/organic interface investigations for photovoltaic devices." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/246263.
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This thesis outlines investigations of metal oxide/organic interfaces in photo-voltaic devices. It focuses on device instabilities originating from the metal oxide layer surface sensitivity and it presents suggested mechanisms behind these in- stabilities. A simple sol-gel solution deposition technique for the fabrication of stable and highly performing transparent conducting mixed metal oxides (ZnMO) is presented. It is demonstrated that the use of amorphous, mixed metal oxides allows improving the performance and stability of interfacial charge extraction layers for organic solar cells. Two novel ternary metal oxides, zinc-strontrium- oxide (ZnSrO) and zinc-barium-oxide (ZnBaO), were fabricated and their use as electron extraction layers in inverted organic photovoltaics is investigated. We show that using these ternary oxides can lead to superior devices by: prevent- ing a dipole forming between the oxide and the active organic layer in a model ZnMO/P3HT:PCBM OPV as well as lead to improved surface coverage by a self assembled monolayer and promote a significantly improved charge separation efficiency in a ZnMO/P3HT hybrid device. Additionally a spectroscopic technique allowing a versatility of characterisa- tion for long-term stability investigations of organic solar cells is reported. A device instability under broadband light exposure in vacuum conditions for an inverted ZnSrO/PTB7:PC71BM OPV is observed. Direct spectroscopic evidence and electrical characterisation indicate the formation of the PC71BM radical an- ion associated with a loss in device performance. A charge transfer mechanism between a heavily doped oxide layer and the organic layers is suggested and dis- cussed.
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Potscavage, William J. Jr. "Physics and engineering of organic solar cells." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39634.
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Organic solar cells have the potential to be portable power sources that are light-weight, flexible, and inexpensive. However, the highest power conversion efficiency for organic solar cells to date is ~8%, and most high-efficiency solar cells have an area of less than 1 cm². This thesis advances the field of organic solar cells by studying the physics and engineering of the devices to understand the reverse saturation current, which is related to efficiency, and the effects of area scaling.
The most commonly accepted models to describe the physics of organic photovoltaic devices are reviewed and applied to planar heterojunction solar cells based on pentacene / C60 as a model system. The equivalent circuit model developed for inorganic solar cells is shown to work well to describe the behavior of organic devices and parameterize their current-voltage characteristics with five parameters. Changes in the parameters with different material combinations or device structures are analyzed to better understand the operation of the presented organic solar cells. A one-dimensional diffusion model for the behavior of excitons and treatment of the organic layers as planes is demonstrated to adequately model the external quantum efficiency and photocurrent in pentacene / C60 solar cells.
The origin of the open-circuit voltage is studied using cells with different electrodes and different donor materials. While changing the electrodes does not affect open-circuit voltage, it is greatly modified by changes in the donor. Tests with additional semiconductors show the change in open-circuit voltage is not consistent from donor to donor as the acceptor is varied, suggesting a more complex relation than just the difference in energy levels. Study of the temperature dependence of the equivalent circuit parameters shows that the reverse saturation current, which has a significant role in determining the open-circuit voltage, has a thermally activated behavior. From this behavior, the reverse saturation current is related back to charge transfer at the donor / acceptor heterojunction to suggest that both the effective energy barrier presented by the energy levels and the electronic coupling are important in determining the reverse saturation current and open-circuit voltage. This marks a shift from just considering a built-in voltage or the energy levels to also considering the electronic coupling of the donor and acceptor materials. Temperature-dependent performance characteristics are also used to show key differences between organic and inorganic devices.
Finally, the effect of area scaling is explored with pentacene / C60 solar cells having areas of 0.11, 7, and 36.4 cm². Analysis with the equivalent circuit model shows that performance decreases as area increases because of an increasing series resistance presented by the transparent electrode. A metal grid, to provide low resistance pathways for current, fabricated on top of the transparent electrode is proposed to reduce the effective resistance. The grid is unique in that it is placed between the electrode and the semiconductor layer and must be passivated to prevent shorts through the thin semiconductor to the back metal electrode. Analysis of the grid predicts greatly reduced series resistance, and experimental results show reduced resistance and improved performance for the 7 cm² and 36.4 cm² devices when including the grid.
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Ghamande, Maithili. "Optical Modeling of Organic Photovoltaic Solar Cells." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1320329919.
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Sahare, Swapnil Ashok. "Enhancing the Photovoltaic Efficiency of a Bulk Heterojunction Organic Solar Cell." TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1609.
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Active layer morphology of polymer-based solar cells plays an important role in improving power conversion efficiency (PCE). In this thesis, the focus is to improve the device efficiency of polymer-based solar cells. In the first objective, active layer morphology of polymer-solar cells was optimized though a novel solvent annealing technique. The second objective was to explore the possibility of replacing the highly sensitive aluminum cathode layer with a low-cost and stable alternative, copper metal. Large scale manufacturing of these solar cells is also explored using roll-to-roll printing techniques.
Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl (PCBM) were used as the active layer blend for fabricating the solar cell devices using bulk heterojunction (BHJ), which is a blend of a donor polymer and an acceptor material. Blends of the donor polymer, P3HT and acceptor, PCBM were cast using spin coating and the resulting active layers were solvent annealed with dichlorobenzene in an inert atmosphere. Solvent annealed devices showed improved morphology with nano-phase segregation revealed by atomic force microscopy (AFM) analysis. The roughness of the active layer was found to be 6.5 nm. The nano-phase segregation was attributed to PCBM clusters and P3HT domains being arranged under the solvent annealing conditions. These test devices showed PCE up to 9.2 % with current density of 32.32 mA/cm2, which is the highest PCE reported to date for a P3HT-PCBM based system.
Copper was deposited instead of the traditional aluminum for device fabrication. We were able to achieve similar PCEs with copper-based devices. Conductivity measurements were done on thermally deposited copper films using the two-probe method. Further, for these two configurations, PCE and other photovoltaic parameters were compared.
Finally, we studied new techniques of large scale fabrication such as ultrasonic spray coating, screen-printing, and intense pulse light sintering, using the facilities at the Conn Center for Renewable Energy Research at the University of Louisville. In this study, prototype devices were fabricated on flexible ITO coated plastics. Sintering greatly improved the conductivity of the copper nano-ink cathode layer. We will explore this technique’s application to large-scale fabrication of solar cell devices in the future work.
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Woods, Kurt Wade. "Solar Energy Conversion and Control Using Organic Photovoltaic Cells." TopSCHOLAR®, 2013. http://digitalcommons.wku.edu/theses/1315.
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Organic photovoltaic (OPV) cells are advanced, newly emerging technologies that are lightweight, mechanically flexible devices with highthroughput processes from low cost material in a variety of colors. Rathnayake et al. of Western Kentucky University have developed a nanostructure-based OPV cell. Presented in this thesis is a model and simulation of a generalized PV powered system that can predict the performance of solar arrays in various environmental conditions. The simulation has been carried out in Matlab/Simulink, and upon entering the cell’s parameters, it provides key electrical characteristics such as the cell’s I-V curve and efficiency information. The total system that is simulated consists of three elements: a universal two-cell solar array that can account for partial shading and manufacturing variation, a current-controlled power converter, and an energy storage device with charging and discharging capabilities.
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Wynands, David. "Strategies for Optimizing Organic Solar Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-65084.
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This work investigates organic solar cells made of small molecules. Using the material system α,ω-bis(dicyanovinylene)-sexithiophene (DCV6T) - C60 as model, the correlation between the photovoltaic active layer morphology and performance of the solar cell is studied. The chosen method for controlling the layer morphology is applying different substrate temperatures (Tsub ) during the deposition of the layer. In neat DCV6T layers, substrate heating induces higher crystallinity as is shown by X-ray diffraction and atomic force microscopy (AFM). The absorption spectrum displays a more distinct fine structure, a redshift of the absorption peaks by up to 11 nm and a significant increase of the low energy absorption band at Tsub = 120°C compared to Tsub = 30°C. Contrary to general expectations, the hole mobility as measured in field effect transistors and with the method of charge extraction by linearly increasing voltage (CELIV) does not increase in samples with higher crystallinity. In mixed layers, investigations by AFM and UV-Vis spectroscopy reveal a stronger phase separation induced by substrate heating, leading to larger domains of DCV6T. This is indicated by an increased grain size and roughness of the topography, the increase of the DCV6T luminescence signal, and the more distinct fine structure of the DCV6T related absorption. Based on the results of the morphology analysis, the effect of different substrate temperatures on the performance of solar cells with flat and mixed DCV6T - C60 heterojunctions is investigated. In flat heterojunction solar cells, a slight increase of the photocurrent by about 10% is observed upon substrate heating, attributed to the increase of DCV6T absorption. In mixed DCV6T : C60 heterojunction solar cells, much more pronounced enhancements are achieved. By varying the substrate temperature from -7°C to 120°C, it is shown that the stronger phase separation upon substrate heating facilitates the charge transport, leading to a significant increase of the internal quantum efficiency (IQE), photocurrent, and fill factor. Consequently, the power conversion efficiency (PCE) increases from 0.5% at Tsub = -7°C to about 3.0 % at Tsub ≥ 77°C. Subsequent optimization of the DCV6T : C60 mixing ratio and the stack design of the solar cell lead to devices with PCE of 4.9±0.2 %. Using optical simulations, the IQE of these devices is studied in more detail to identify major remaining loss mechanisms. The evaluation of the absorption pattern in the wavelength range from 300 to 750 nm shows that only 77 % of the absorbed photons contribute to the exciton generation in photovoltaic active layers, while the rest is lost in passive layers. Furthermore, the IQE of the photovoltaic active layers, consisting of an intrinsic C60 layer and a mixed DCV6T : C60 layer, exhibits a lower exciton diffusion efficiency for C60 excitons compared to DCV6T excitons, attributed to exciton migration into the adjacent electron transport layerDiese Arbeit befasst sich mit organischen Solarzellen aus kleinen Molekülen. Anhand des Materialsystems α,ω-bis(Dicyanovinylen)-Sexithiophen (DCV6T) - C60 wird der Zusammenhang zwischen Morphologie der photovoltaisch aktiven Schicht und dem Leistungverhalten der Solarzellen untersucht. Zur Beeinflussung der Morphologie werden verschiedene Substrattemperaturen (Tsub ) während des Schichtwachstums der aktiven Schicht eingestellt. Beim Heizen des Substrates weisen DCV6T Einzelschichten eine erhöhte Kristallinität auf, die mittels Röntgenbeugung und Rasterkraftmikroskopie (AFM) erkennbar ist. Zudem bewirkt die Erhöhung der Substrattemperatur von 30°C auf 120°C eine ausgeprägtere Feinstrukturierung des Absorptionsspektrums, eine Rotverschiebung um bis zu 11 nm und eine Verstärkung der niederenergetischen Absorptionsbande. Entgegen den Erwartungen wird weder in Feldeffekttransistoren noch mit der Methode der Ladungsextraktion bei linear steigenden Spannungspulsen (CELIV) eine Verbesserung der Löcherbeweglichkeit in Zusammenhang mit der erhöhten Kristallinität gemessen. Mischschichten mit C60 weisen bei erhöhten Substrattemperaturen eine stärkere Phasentrennung auf, die zu größeren DCV6T Domänen innerhalb der Schicht führt. Dieser Effekt wird zum Einen durch größere Körnung und Rauigkeit der Topographie, zum Anderen durch die Erhöhung des Lumineszenzsignals von DCV6T sowie der Ausprägung der Feinstruktur im Absorptionsspektrum nachgewiesen. Ausgehend von den Ergebnissen der Morphologieuntersuchung werden die Auswirkungen von verschiedenen Substrattemperaturen auf das Leistungsverhalten von DCV6T - C60 Solarzellen mit planarem und Volumen-Heteroübergang analysiert. Solarzellen mit planarem Heteroübergang weisen eine geringe Verbesserung des Photostromes von etwa 10 % beim Heizen des Substrates auf. Diese wird durch die Erhöhung der DCV6T Absorption verursacht. In Volumen-Heteroübergängen führt die stärkere Phasentrennung bei steigender Substrattemperatur im untersuchten Temperaturbereich von -7°C bis 120°C zu einer Verbesserung des Ladungsträgertransports. Dadurch verbessern sich die interne Quanteneffizienz (IQE), der Photostrom und der Füllfaktor. Der Wirkungsgrad der Solarzellen erhöht sich von 0.5 % bei Tsub = -7°C auf 3.0 % bei Tsub ≥ 77°C. Eine weitere Optimierung des DCV6T : C60 Mischverhältnisses und des Schichtaufbaus ermöglicht Solarzellen mit Wirkungsgraden von 4.9±0.2 %. Mittels optischer Simulationen wird die IQE dieser Solarzellen näher untersucht, um verbleibende Verlustmechanismen zu identifizieren. Es ergibt sich, dass innerhalb des Wellenlängenbereichs von 300 bis 750 nm nur 77 % der absorbierten Photonen tatsächlich in den photovoltaisch aktiven Schichten absorbiert werden, während der Rest in nicht aktiven Schichten verloren geht. Des Weiteren kann nachgewiesen werden, dass C60 Exzitonen aus der aktiven Schicht, bestehend as einer intrinsischen C60 Schicht und einer DCV6T : C60 Mischschicht, durch Diffusion in die angrenzende Elektronentransportschicht verloren gehen
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Dindar, Amir. "Microfabrication of organic electronic devices: organic photovoltaic module with high total-area efficiency." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53582.
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Transferring organic photovoltaics (OPV) from the laboratory into economically feasible products, requires the fabrication of modules, a series of connected single cells. During this transition, there is typically a drastic decrease in power conversion efficiency (PCE). This thesis reports on the design, fabrication, and characterization of state-of-the-art, high-performance organic photovoltaic modules with a novel geometry that composed of unit cells with alternating electrical polarities. Such configuration is realized by exclusive patterning of the interlayers and electrodes and avoids patterning of the photoactive layer. With this novel architecture, area losses of photovoltaic module can be significantly reduced compared with the conventional configurations. The processing of this new solar cell module is also compatible with large area processing techniques such as slot-die coating. This thesis reports on 4-cell and 8-cell modules, wherein the measured fill-factors (FF) and PCE of the constituent sub-cells and of the modules are almost identical. The 4-cell module, with a total area of 0.8 cm2, exhibits an open-circuit voltage (VOC) of 3.15 V, a short circuit-current density (JSC) of 2.3 mA/cm2 and a FF of 0.69, yielding a PCE of 5.01%. The 8-cell module, with a total area of 1.6 cm2, exhibits a VOC of 6.39 V, a JSC of 1.2 mA/cm2 and a FF of 0.63, yielding a PCE of 5.06%. Similar PCE values between 4-cell and 8-cell module is a demonstration of scalability of this novel geometry without compromising the efficiency.
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Greenbank, William. "Interfacial stability and degradation in organic photovoltaic solar cells." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0338/document.
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Les durées de vie des cellules solaires photovoltaïques organiques (OPV) doivent être améliorées afin que cette technologie puisse être commercialisée sur une grande échelle. Ce travail étudie l’influence de la sélection des matériaux pour l’interface supérieure sur la dégradation des OPV inversées. La première partie de cette étude s’occupe des effets de la dégradation thermale. Il a été constaté que la tension de circuit-ouvert (VOC) et le facteur de forme (FF) diminuent lors du vieillissement des OPVs ayant une HTL de MoO3 et une électrode d’argent. Des expériences de caractérisation physique ont mis en évidence que les électrodes d’argent démouillent lors du vieillissement thermique ce qui peut conduire à la mort rapide des cellules avec des électrodes minces. Des analyses de rupture ont également faites. Il a été constaté que l’adhésion d’interface supérieure augmente fortement dans les échantillons avec électrode en argent due à la diffusion de matière, et il est possible qu’il y ait une relation entre cette diffusion et la perte de VOC et FF. Dans la deuxième partie, les effets de la lumière sur la dégradation et l’influence de la présence d’oxygène ou d’humidité ont été étudiés. Quelques effets des matériaux ont été notés, en particulier sur la durée de vie. L’oxygène a eu l’effet d’accélérer notablement la dégradation, et aucune différence n’a été notée selon les matériaux utilisés. En revanche, l’humidité a eu un effet prononcé sur les échantillons avec certains HTLs. Ce travail souligne l’importance de penser à la durée de vie quand on désigne les dispositifs OPV, en particulier pour sélectionner des matériaux appropriés afin d’optimiser la durée de vieOrganic photovoltaic (OPV) solar cells show great promise but suffer from short operating lifetimes. This study examines the role that the selection of materials for the hole extraction interface in inverted OPV devices plays in determining the lifetime of a device. In the first part of the study, the effects of thermal degradation were examined. It was found that devices containing MoO3 HTLs and silver top electrodes exhibit an open-circuit voltage (VOC)/fill factor (FF)-driven mechanism. Physical characterisation experiments showed that, with heating, the silver electrode undergoes de-wetting. With thin electrodes this can result in the catastrophic failure of the device. A fracture analysis study found that silver-containing devices experience an increase in adhesion of their top layers to the active layer due to interdiffusion between the layers. This interdiffusion may be related to the loss of VOC and FF in Ag/MoO3 devices through diffused species forming charge traps in the active layer. In the second part of the study, the effects of photodegradation in different atmospheres were studied. Some material-dependent effects were observed when the devices were aged in an inert atmosphere, including variations in projected lifetime. The effect of oxygen was to greatly accelerate degradation, and remove any of the material-dependence observed in the inert experiment, while humidity led to a substantial increase in the degradation rate of devices containing PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate). This study underlines the importance of considering device lifetime in device design, and choosing materials to minimise degradation
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Sutcu, Sinan Mahmut. "The effects of ITO surface modification on lifetime in organic photovoltaic devices and a test setup for measuring lifetime." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34685.
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Though relatively young, the field of organic electronics is a rapidly growing market and considerable research is being done in creating a whole range of devices from organic molecules from organic field effect transistors to LEDs to photovoltaic devices. The field of organic photovoltaic in particular has become important in recent years with the push for newer, renewable sources of energy to end the dependence on fossil fuels. While the efficiencies of organic photovoltaic devices continue to rise, one barrier to their commercial adoption has been the limited lifetimes of these devices. While certain degradation methods of organic photovoltaics, such as photo-oxidation, have been extensively studied and solutions to these problems, such as encapsulation, are being researched, certain other degradation mechanisms are less understood and studied. The focus of this thesis is on one such degradation mechanism, UV degradation, specific to the ITO-pentacene interface in pentacene/C60 organic photovoltaic devices. Attempts were made to increase the lifetime of the devices by using phosphonic acids or oxygen plasma to modify the surface of the ITO. While conducting these experiments, the lack of a system to test the lifetime of multiple devices for long periods of time became apparent. As such as system was a requirement for future research into the lifetimes of organic photovoltaic devices a system was designed and built. The system would operate the photovoltaic device in a way comparable to its end-use and would allow over 100 devices to be tested simultaneously for durations exceeding 10,000 hours if necessary. This system would allow for statistically significant lifetime testing to be carried out in the future.
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Tvingstedt, Kristofer. "Light Trapping and Alternative Electrodes for Organic Photovoltaic Devices." Doctoral thesis, Linköpings universitet, Biomolekylär och Organisk Elektronik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17229.
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Organic materials, such as conjugated polymers, have emerged as a promising alternative for the production of inexpensive and flexible photovoltaic cells. As conjugated polymers are soluble, liquid based printing techniques enable production on large scale to a price much lower than that for inorganic based solar cells. Present day state of the art conjugated polymer photovoltaic cells are comprised by blends of a semiconducting polymer and a soluble derivative of fullerene molecules. Such bulk heterojunction solar cells now show power conversion efficiencies of up to 4-6%. The quantum efficiency of thin film organic solar cells is however still limited by several processes, of which the most prominent limitations are the comparatively low mobility and the high level of charge recombination. Hence organic cells do not yet perform as well as their more expensive inorganic counterparts. In order to overcome this present drawback of conjugated polymer photovoltaics, efforts are continuously devoted to developing materials or devices with increased absorption or with better charge carrier transporting properties. The latter can be facilitated by increasing the mobility of the pure material or by introducing beneficial morphology to prevent carrier recombination. Minimizing the active layer film thickness is an alternative route to collect more of the generated free charge carriers. However, a minimum film thickness is always required for sufficient photon absorption. A further limitation for low cost large scale production has been the dependence on expensive transparent electrodes such as indium tin oxide. The development of cheaper electrodes compatible with fast processing is therefore of high importance. The primary aim of this work has been to increase the absorption in solar cells made from thin films of organic materials. Device construction, deploying new geometries, and evaluation of different methods to provide for light trapping and photon recycling have been strived for. Different routes to construct and incorporate light trapping structures that enable higher photon absorption in a thinner film are presented. By recycling the reflected photons and enhancing the optical path length within a thinner cell, the absorption rate, as well as the collection of more charge carriers, is provided for. Attempts have been performed by utilizing a range of different structures with feature sizes ranging from nanometers up to centimeters. Surface plasmons, Lambertian scatterers, micro lenses, tandem cells as well as larger folded cell structures have been evaluated. Naturally, some of these methods have turned out to be more successful than others. From this work it can nevertheless be concluded that proper light trapping, in thin films of organic materials for photovoltaic energy conversion, is a technique capable of improving the cell performance. In addition to the study of light trapping, two new alternative electrodes for polymer photovoltaic devices are suggested and evaluated.
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ANUSIT, KAEWPRAJAK. "Improvement of Photovoltaic Properties of Solar Cells with Organic and Inorganic Films Prepared by Meniscuc Coating Technique." Kyoto University, 2019. http://hdl.handle.net/2433/242322.
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Pandey, Laxman. "Theoretical studies of the structure-property relationships of hole- and electron-transport materials for organic photovoltaic applications." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48964.
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Donor-acceptor and thiophene based π-conjugated molecules and polymers, along with fullerene derivatives, are extensively used active components in the photoactive layer of organic photovoltaic devices. In this dissertation, we make use of several computational methodologies to investigate structure-property relationships of these organic systems in their molecular forms. We begin with an overview of the field of organic photovoltaics and some of the important problems in organic solar cells that are currently being investigated. This is then followed by a brief review of the electronic-structure methods (e.g. Hartree-Fock theory, Density Functional Theory, and Time-dependent Density Functional Theory) that are employed.
We then present the main results of the dissertation. Chapter 3 provides a broad overview on how changes to the donor-acceptor copolymer chemical structure impacts its intrinsic geometric, electronic, and optical properties. Chapter 4 focuses on the characterization of the lowest excited-states and optical absorption spectra in donor-acceptor copolymers. In Chapter 5, we investigate the effects of alkyl side-chain placements in the π-conjugated backbone of oligothiophenes and how that impacts their intramolecular properties as well as the oligomer:fullerene interfacial interactions. Chapter 6 presents our investigation on the role of oligomer:fullerene configuration and reorganization energy on exciton-dissociation and charge-recombination processes. Finally, a synopsis of the work and further considerations are presented in Chapter 7.
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Patel, Dinesh G. "Organic dyes for photoswitching and photovoltaic applications /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8537.
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Kim, Yongjin. "Experimental investigation of the interfacial fracture toughness in organic photovoltaics." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47605.
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The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.
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Mao, Zhenghao. "Molecular Structures and Device Properties of Organic Solar Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1395332071.
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Bergqvist, Jonas. "Microstructure and Temperature Stability of APFO-3:PCBM Organic Photovoltaic Blends." Thesis, Linköping University, Biomolecular and Organic Electronics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-58559.
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In this thesis, the microstructure of organic photovoltaic APFO-3:PC61BM bulk-heterojunction blends was examined. Earlier studies have focused on the microstructure after spin coating. This thesis aims to give a better insight into microstructural degradation as the films are annealed above the glass transition temperature, Tg, and the mixture approaches thermodynamic equilibrium. Electro- and photoluminescence studies indicate that the polymer and PC61BM are intermixed on a scale shorter than the exciton diffusion length of 10 nm, even when annealed above Tg. The temperature stability of APFO-3:PC61BM was also investigated with respect to the molecular weight of the polymer. The photovoltaic performance of these blends was found to be stable up to temperatures approaching the glass transition temperature, especially if a high molecular-weight APFO-3 grade was used.
The crystallization of PC61BM was also investigated. Above Tg, PC61BM crystallization was found to commence, albeit slowly at temperatures close to Tg. At elevated temperatures instead, micrometer sized crystals were observed to form. It was also noted that illumination while annealing APFO-3:PC61BM thin films above Tg affected PC61BM crystallization, the origin of which is so far unclear although chemical degradation could be largely excluded.
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Apaydin, Dogukan Hazar. "Electrochromic And Photovoltaic Applications Of Conjugated Polymers." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614481/index.pdf.
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Three new azobenzene containing conjugated monomers were designed and synthesized. Resulting monomers were characterized by means of 1H NMR and 13C NMR techniques. Monomers (E)-1,2-bis(4-(thiophen-2-yl)phenyl)diazene (M1), (E)-1,2-bis(4-(4-hexylthiophen-2-yl) phenyl) diazene (M2) and (E)-1,2-bis(2-fluoro-4-(4-hexylthiophen-2-yl)phenyl) diazene (M3) were electrochemically polymerized using cyclic voltammetry to give polymers P1, P2 and P3. The polymers were subjected to spectroelectrochemical and kinetic studies in order to obtain information about their elecrochromic characteristics. P1 and P2 were pale-yellow in their neutral states and blue in oxidized states while P3 showed multichromic property due to having polaron bands in visible region of the spectrum. Addition of fluorine atoms to the backbone of P3, lowered the LUMO level of P3 thus gained the polymer n-doping property.
In the second part of this thesis poly((9,9-dioctylfluorene)-2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl-benzo[1,2,3]triazole)) (PFTBT) polymer was mixed with common electron acceptor Phenyl-C61-butyric acid methyl ester (PCBM) and used in organic solar cell applications. Active layers containing PFTBT and PCBM were spin casted on ITO coated substrates at varying rotational speeds to obtain active layer thicknesses having different values. Thickness of the active layer was optimized so was the efficiency of organic solar cells. As a result of this optimization study, efficiency of PFTBT containing organic solar cells were increased to 1.06% which is a higher value than previosly reported literature results.
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Tang, Zheng. "Studies of Inverted Organic Solar Cells Fabricated by Doctor Blading Technique." Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54141.
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Over the last few decades, bulk-heterojunction organic photovoltaic devices comprising an intimately mixed donor-acceptor blend have gained serious attention due to their potential for being cheap, light weight, flexible and environmentally friendly. In this thesis, APFO-3/PCBM bulk-heterojunction based organic photovoltaic devices with an inverted layer sequence were investigated systematically. Doctor blade coating is a technique that is roll-to-roll compatible and cost efficient and has been used to fabricate the solar cells.
Initial studies focused on optimization of the electrodes. A thin film of the conductive polymer PEDOT:PSS was chosen to be the transparent anode. Different PEDOT:PSS films with respect to the film thickness and deposition temperature were characterized in terms of conductivity and transmission. Decent conductance and transmittance were obtained in the films deposited with wet film thickness setting of 35 μm, The cathode was fabricated from a metal bilayer comprising Al and Ti with an area about 1 cm2, and the best-working cathodes contained a 70 nm thick Al layer covered by a thin Ti layer of about 10 -15 nm.
Optimized coating temperature and wet film thickness settings for the active layer and PEDOT:PSS layer were experimentally determined. The highest efficiency of the APFO-3/PCBM based inverted solar cells fabricated by doctor blading was 0.69%, which exceeded the efficiency of spin-coated inverted cells.
A higher efficiency (0.8 %) was achieved by adding a small amount of high molecular weight polystyrene to the active layer. Morphological changes after adding of the polystyrene were observed by optical microscopy and AFM. A coating temperature dependent phase separation of the APFO-3/PCBM/polystyrene blend was found.
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Shu, Ying. "NOVEL SOLUTION PROCESSABLE ACCEPTORS FOR ORGANIC PHOTOVOLTAIC APPLICATIONS." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/135.
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The field of organic electronics has become an increasingly important field of research in recent years. Organic based semiconductors have the potential for creating inexpensive, solution processed devices on flexible substrates. Some of the applications of organic semiconductors include organic field effect transistors, organic light emitting diodes and organic photovoltaics.
Functionalized pentacenes have been proven to be viable donor materials for use in organic photovoltaic devices. The goal of this research is to synthesize and test the viability of novel electron deficient pentacenes and pentacene based materials as acceptors to be used as drop-in replacements for PCBM in bulk-heterojunction organic solar cells.
Our goal was to tune and improve the efficiencies of these solar cells in a two pronged approach. First we tuned the open circuit voltage of these devices by determining the optimal energy levels of these acceptors by varying the number of electron withdrawing substituents on the acene core. We also tuned the short circuit current by chemically altering the solid state packing and optimizing device processing conditions. A preliminary structure-property relationship of these small molecule acceptors and photovoltaic device efficiency was established as a result.
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Daoud, Walid. "Synthesis of conjugated polymers and their use in photovoltaic cells." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/14469/.
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MacDonald, Gordon Alex. "Nanoscale Characterization of the Electrical Properties of Oxide Electrodes at the Organic Semiconductor-Oxide Electrode Interface in Organic Solar Cells." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/347338.
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This dissertation focuses on characterizing the nanoscale and surface averaged electrical properties of transparent conducting oxide (TCO) electrodes such as indium tin oxide (ITO) and transparent metal-oxide (MO) electron selective interlayers (ESLs), such as zinc oxide (ZnO), the ability of these materials to rapidly extract photogenerated charges from organic semiconductors (OSCs) used in organic photovoltaic (OPV) cells, and evaluating their impact on the power conversion efficiency (PCE) of OPV devices. In Chapter 1, we will introduce the fundamental principles regarding the need for low cost power generation, the benefits of OPV technologies, as well as the key principles that govern the operation of OPV devices and the key innovations that have advanced this technology. In Chapter 2 of this dissertation, we demonstrate an innovative application of conductive probe atomic force microscopy (CAFM) to map the nanoscale electrical heterogeneity at the interface between an electrode, such as ITO, and an OSC such as the p-type OSC copper phthalocyanine (CuPc).(MacDonald et al. (2012) ACS Nano, 6, p. 9623) In this work we collected arrays of J-V curves, using a CAFM probe as the top contact of CuPc/ITO systems, to map the local J-V responses. By comparing J-V responses to known models for charge transport, we were able to determine if the local rate-limiting step for charge transport is through the OSC (ohmic) or the CuPc/ITO interface (nonohmic). These results strongly correlate with device PCE, as demonstrated through the controlled addition of insulating alkylphosphonic acid self-assembled monolayers (SAMs) at the ITO/CuPc interface. Subsequent chapters focus on the electrical property characterization of RF-magnetron sputtered ZnO (sp-ZnO) ESL films on ITO substrates. We have shown that the energetic alignment of ESLs and the organic semiconducting (OSC) active materials plays a critical role in determining the PCE of OPV devices and the appearance of, or lack thereof, UV light soaking sensitivity. For ZnO and fullerene interfaces, we have shown that either minimizing the oxygen partial pressure during ZnO deposition or exposure of ZnO to UV light minimizes the energetic offset at this interface and maximizes device PCE. We have used a combination of device testing, device modeling, and impedance spectroscopy to fully characterize the effects that energetic alignment has on the charge carrier transport and charge carrier distribution within the OPV device. This work can be found in Chapter 3 of this dissertation and is in preparation for publication. We have also shown that the local properties of sp-ZnO films varies as a function of the underlying ITO crystal face. We show that the local ITO crystal face determines the local nucleation and growth of the sp-ZnO films. We demonstrate that this effects the morphology, the chemical resistance to etching as well as the surface electrical properties of the sp-ZnO films. This is likely due to differences in the surface mobility of sputtered Zn and O atoms on these crystal faces during film nucleation. This affects the nanoscale distribution of electrical and chemical properties. As a result we demonstrate that the PCE, and UV sensitivity of the J-V response of OPVs using sp-ZnO ESLs are strongly impacted by the distribution of ITO crystal faces at the surface of the substrate. This work can be found in Chapter 4 of this dissertation and is in preparation for publication. These studies have contributed to a detailed understanding of the role that electrical heterogeneity, insulating barriers and energetic alignment at the MO/OSC interface play in OPV PCE.
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Müller, Toni. "Infrared Absorber Materials in Organic Small Molecule Solar Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-178375.
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Broadening the spectrum available to solar cells towards infrared wavelengths is one way to increase efficiency of organic solar devices. This thesis explores the possibilities of these organic heterojunction devices and two different material classes in thin films and organic solar devices: tin phthalocyanines (SnPcs) and aza-bodipys. To estimate the efficiency reachable under sunlight, model calculations are done for single and tandem cells. These calculations include a distinction between the optical gap and the electrical gap and the splitting of the quasi-Fermi levels. With a number of assumptions, e.g. a fill factor (FF) and an external quantum efficiency (EQE) within the absorption range of 65%, the resulting efficiencies are 15% in a single cell and of 21% in a tandem cell. Halogenation is known to lower the energy levels of molecules without chang-ing the optical band gap. Three different fluorinated and chlorinated SnPcs are investigated and compared to the neat SnPc. While chlorination of SnPc worsens the transport properties of the active layer leading to a lowered FF, the fluorina-tion of SnPc results in the intended increase in VOC and, consequently, efficiency for planar heterojunctions. In bulk heterojunction, however, fluorination does not change the efficiency probably due to the unstably bound fluorine. One method to modify the ionization potential (IP) and the absorption of the second material class, the aza-bodipys, is the annulation of the benzene ring. The energy levels determined by CV and UPS measurement and DFT-calculation show very good agreement and can be linked to a decrease in VOC: The Ph4-bodipy (not benzannulated) device has an efficiency of 1.2% with an EQE reaching up to 800nm and a VOC of almost 1V. The Ph2-benz-bodipy device shows a Voc of 0.65V and an efficiency of 1.1%, the EQE reaching up to 860nm. The variation of the molecule’s end groups to vary their IP is successfully employed for three different benz-bodipys: The variation results in a decrease of the optical gap from 1.5eV for the phenyl group, to 1.4eV for the MeO group, and 1.3eV for the thiophene group with the effective gap and the VOC following this trend. Efficiencies of 1.1% and 0.6% in combination with C60 can be reached in mip-type devices. Ph2-benz-bodipy is then optimized into a single cell with an efficiency of 2.9%. In a tandem cell with DCV6T-Bu4:C60, a Voc of 1.7V, a FF of 57% and an efficiency of 5% is reachedDie Erweiterung des verfügbaren Spektrums in den Infrarotbereich ist eine Möglichkeit, die Effizienz organischer Solarzellen zu erhöhen. Diese Arbeit erkundet das Potential dieser Heteroübergänge und zwei Materialklassen in dünnen Schichten und Bauelementen: Zinnphthalozyanine (SnPc) und aza-Bodipys. Um die potentielle Effizienz abzuschäötzen, werden Modellberechnungen für Einzel- und Tandemzellen durchgeführt, unter Berücksichtigung des Unterschieds von optischer und elektrischer Bandlücke und der Quasiferminiveauaufspaltung. Mithilfe einiger Annahmen (z.B. Füllfaktor (FF) und externe Quanteneffizienz (EQE) gleich 65%) lässt sich die Einzelzelleffizienz auf 15%, die Tandemzelleffizienz auf 21% abschätzen. Halogenierung kann die Energieniveaus organischer Moleküle herabsetzen, ohne die optische Bandlücke zu verändern. Drei verschiedene chlorierte und fluorierte SnPcs werden mit dem reinen SnPc verglichen. Während die Chlorierung die Transporteigenschaften der aktiven Schicht und den FF verschlechtern, erhöht die Fluorierung wie erwartet Leerlaufspannung (VOC) und Effizienz im flachen Übergang, nicht jedoch in der Mischschicht, vermutlich aufgrund des nicht stabil gebundenen Fluors. Ein Weg, Ionisationspotential (IP) und Absorption der aza-Bodipy zu verändern, ist die Anelierung des Benzenrings. Die durch CV und UPS ermittelten und mittels DFT errechneten Energieniveaus stimmen gut überein und führen zu einer Verringerung der VOC: Die Zelle mit nichtaniliertem Ph4-bodipy zeigt eine Effizienz von 1.2%; das EQE reicht bis 800nm, die VOC beträgt fast 1V. Die Ph2-benz-bodipy-Zelle zeigt eine VOC von 0.65V und eine Effizienz von 1.1%, das EQE reicht bis 860nm. Der Austausch der Endgruppen zur Vergrößerung des IP, erfolgreich angewandt auf drei Benz-Bodipy-Verbindungen, führt zu einer Verringerung der optischen Bandlücke: von 1.5eV (Phenyl) über 1.4eV (MeO) zu 1.3eV (Thiophen); effektive Bandlücke und Voc folgen diesem Trend. Effizienzen von 1.1% und 0.6% in Kombination mit C60 werden in mip-Zellen erreicht. Ph2-benz-bodipy zeigt in einer optimierten nip-Zelle sogar eine Effizienz von 2.9%. Eine Tandemzelle mit DCV6T-Bu4:C60 zeigt eine Voc von 1.7V, einen FF von 57% und eine Effizienz von 5%
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Mulderig, Andrew J. "Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1457619609.
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Ward, Alexander J. "Using time-resolved fluorescence to investigate exciton harvesting in organic photovoltaic blends." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/11945.
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This thesis is an investigation of the photophysical processes that occur in organic photovoltaic blends in the time between light being absorbed and free charges being generated. The purpose of all solar cells is to generate a photocurrent. The free charges, as they flow out of the device, make up the photocurrent, so understanding the processes by which they are created is vitally important to organic photovoltaic research. The main experimental method used was time-resolved fluorescence spectroscopy. This technique was used to probe the exciton population with respect to time for a variety of blends of organic semiconductors, including the high performance photovoltaic materials PCDTBT, PTB7, C71-PCBM and P3HT. The main goal of the work was to characterise the exciton diffusion lengths of these materials by developing a technique called volume quenching. Volume quenching involves blending a small quantity of quenching material into a thin film of semiconducting material. These introduced quenching sites render excitons unemissive on contact. Thus, from the drop in fluorescence compared with the ‘unquenched' material, it was possible to work out what proportion of the initial excitons have encountered a quenching site in the blends. The results can then be fitted to quantify how diffusive the excitons are -i.e. how far they move. By looking at the rate constant of the quenching process and how it varies with respect to time, quencher concentration and quencher type, it was possible to generate a wealth of additional information, not just about exciton diffusion, but about all the inter-related processes that contribute to exciton harvesting. These processes included the measurement of long-range energy transfer from the donor to the acceptor, electron transfer at the interface with the acceptor and the understanding of nanomorphology of donor-acceptor heterojunctions.
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Ho, Carr Hoi Yi. "Toward better performing organic solar cells: impact of charge carrier transport and electronic interactions in bulk heterojunction blends /Ho Hoi Yi, Carr." HKBU Institutional Repository, 2017. https://repository.hkbu.edu.hk/etd_oa/359.
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Organic photovoltaic (OPV) is an exciting energy harvesting technique. Although its power conversion efficiency (PCE) now exceeds 10% in a research laboratory, the processing window of an OPV cell is still narrow. A fundamental understanding of the OPV materials is desired. This thesis presents the charge carrier transport properties and electronic interactions in the bulk heterojunction (BHJ) active layer of OPV cells. They were found to be well correlated with OPV device performances. Space-charge-limited current (SCLC) measurements and admittance spectroscopy (AS) were employed to study the charge transports, while photothermal deflection spectroscopy (PDS) was used to probe the trap densities inside the materials. Beneficial effects of a common solvent additive, 1,8-diiodooctance (DIO), on PTB7:PC71BM OPV cells have been investigated. With DIO present in the casting solution, the resulting BHJ films have much enhanced electron mobilities, whereas the impact on the hole mobility is negligible. The origin of increased electron mobility is the reduced average electron hopping distance for those films prepared with DIO solvent additive. A balance of hole-electron mobility by tuning the DIO concentration was demonstrated to be the way to optimize the OPV device performance. In light of carrier transport measurement results, a "polymer-rich" strategy with preserved device performance was demonstrated. After understanding the importance of balanced hole-electron mobility, the impact of donor-acceptor weight ratio on the performance of PTB7 : PC71BM based OPV cells was explored. Early stage electronic donor-acceptor interactions were revealed using ultra-low dosages of fullerenes. Before electron transport pathways percolate, the unconnected fullerene domains act as traps and hinder electron transport. From PDS, the trap density observed inside BHJ films was found to be anti-correlated with the fill factor of OPV devices. The origin of low FFs is mainly due to electron traps and localized states from fullerenes. Based on the observations, it is proposed that PC71BM tends to intercalate with PTB7 backbone instead of forming self-aggregates before the electron pathway percolation. Apart from investigating the fundamentals in OPV devices, a solution to improve its processing window was proposed in this thesis. Thermally stable polymer : fullerene OPV cells were fabricated by employing fluorenone-based solid additives. A charge transfer interaction between the additives and donor moiety of polymer formed a locked network which freezes the BHJ morphology under thermal stress. The most promising result retains 90% of the origin efficiency, upon thermal aging at 100 °C for more than 20 hours in PTB7:PC71BM solar cells. Besides fullerene-based OPV, all-polymer photovoltaic solar cells (all-PSCs) were also investigated. Two new difluorobenzene-naphthalene diimide based polymer electron acceptors, one random (P1) and one regioregular (P2) structure, were compared. P2 exhibited a much better molecular packing, a higher electron mobility and more balanced hole-electron mobilities in its composite film with polymer donor, PTB7-Th. An optimized PTB7-Th:P2 device can achieve a respectably high PCE over 5% for all-PSC devices. These all-PSCs should open a new avenue for next generation OPVs.
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Qiao, Qiquan. "Green Organic Solar Cells from a Water Soluble Polymer and Nancrystalline TiO2." VCU Scholars Compass, 2006. http://scholarscompass.vcu.edu/etd/1078.
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The cost of the present generation of inorganic silicon solar cells is very high and further breakthroughs in cost and efficiency using traditional materials are becoming less and less likely after over 50 years of development. Next generation organic solar cells offer a solution to the limitations of silicon through the vision of low-cost, liquid-based, large area fabrication technology based on polymer and nanomaterials at room temperature. However, most polymers used in solar cells are dissolved in organic solvents such as xylene, toluene, chloroform, and chlorobenzene. Such solvents are harmful to people and environments, leading to higher costs due to complicated waste disposal processing. This is in conflict with the low cost, green, and renewable energy for which we are aiming. To realize a green organic solar cell, a novel solar cell has been created using an environmentally friendly water-soluble thiophene polymer [(Sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate])] (PTEBS) and nanocrystalline TiO2. This novel system has shown great potential in photovoltaics the work has garnered the attention of the international community.In our innovative solar cells, the water-soluble polythiophene (PTEBS) is used as electron donor. Nanoparticle TiO2 acts as electron acceptor. PTEBS/TiO2 solar cells with various structures including bilayer heterojunctions, bulk heterojunctions and a hybrid of bilayer and bulk heterojunctions have been developed and explored. These results are comparable to the best polymer/metal-oxide solar cells reported by other groups using organic solvents.In summary, this is the first time that green solar cells have been fabricated from environmentally friendly water-soluble polymers. By using water as the solvent and utilizing liquid-based processing, the cost of the energy generated by this type of solar cell will be further lowered. In addition, the flexible polymer offers the ease of fabrication and integration into different devices.
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Anselmo, Ana Sofia. "The morphology of polyfluorene : fullerene blend films for photovoltaic applications." Licentiate thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-7950.
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Polymer photovoltaic systems whose photoactive layer is a blend of a semiconducting polymer with a fullerene derivative in a bulk heterojunction configuration are amongst the most successful organic photovoltaic devices nowadays. The three-dimensional organization in these layers (the morphology) plays a crucial role in the performance of the devices. Detailed characterization of this organization at the nanoscale would provide valuable information for improving future material and architectural design and for device optimization. In this thesis, the results of morphology studies of blends of several polyfluorene copolymers (APFOs) blended with a fullerene derivative are presented. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was combined with dynamic Secondary Ion Mass Spectrometry (dSIMS) for surface and in-depth characterization of the blend films. NEXAFS was performed using two different electron detection methods, partial (PEY) and total (TEY) electron yield, which provide information from different depth regimes. Quantitative compositional information was obtained by fitting the spectra of the blend films with a linear combination of the spectra of films of the pure components. In blends of APFO3 with PCBM in two different blend ratios (1:1 and 1:4 of polymer:fullerene) NEXAFS data show the existence of compositional gradients in the vertical direction for both blend ratios, with clear polymer enrichment of the free surface. A series of APFOs with systematic changes in the side-chains was studied and it was shown that those small modifications can affect polymer:fullerene interaction and induce vertical phase separation. Polymer-enrichment of the free surface was clearly identified, in accordance with surface energy minimization mechanisms, and a compositional gradient was revealed already in the first few nanometers of the surface of the blend films. dSIMS showed that this vertical phase separation propagates throughout the film. It was possible to determine that as the polar character of the polymer increases, and thus the polymer:fullerene miscibility is improved, the tendency for vertical phase separation becomes stronger.Paper II was not published at the time of the licentiate defence and had the title: NEXAFS spectroscopy study of the surface composition in APFO3:PCBM blend films
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Rathod, Siddharth Narendrakumar. "Structure Stability and Optical Response of Lead Halide Hybrid Perovskite Photovoltaic Materials: A First-Principles Simulation Study." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1496189488934021.
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Noori, Keian. "Energy-level alignment at organic and hybrid organic-inorganic photovoltaic interfaces." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d1b2a4e9-a5d6-4843-b172-6d83dea8a6cb.
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Organic and hybrid organic-inorganic photovoltaic (PV) devices have the potential to provide low-cost, large scale renewable energy. Despite the tremendous progress that has been made in this field, device efficiencies remain low. This low efficiency can be partly attributed to the low open-circuit voltages (Voc) generated by organic and hybrid organic-inorganic PV devices. The Voc is critically determined by the energy-level alignment at the interface between the materials forming the device. In this thesis we use first-principles methods to explore the energy-level alignment at the interfaces between the conjugated polymer poly(3-hexylthiophene) (P3HT) and three electron acceptors, zinc oxide (ZnO), gallium arsenide (GaAs) and graphene. We find that Voc reported in the literature for ZnO/P3HT devices is significantly lower than the theoretical maximum and that the interfacial electrostatic dipole plays an important role in the physics underlying the charge transfer at the heterojunction. We note significant charge transfer from the polymer to the semiconductor at GaAs/P3HT interfaces, and use this result to help interpret experimental data. Our findings support the conclusion that charge transferred from P3HT to GaAs nanowires can passivate the surface defect states of the latter and, as a result, account for the observed decrease in photoluminescence lifetimes. Finally, we explore the energy-level alignment at the graphene/P3HT interface and find that Voc reported for experimental devices is in line with the theoretical maximum. The effect of functionalised graphene is also examined, leading to the suggestion that functionalisation might have important consequences for device optimisation.
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Chu, Cheng-Che. "Hydrogen-bonded supramolecular materials for organic photovoltaic applications." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13866/document.
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Dans ce manuscrit est décrite l'utilisation d'interactions supramoléculaires pour diriger l'auto-assemblage de composés donneurs et accepteurs d'électrons au sein de dispositifs photovoltaïques organiques. Dans ce but, des matériaux de type oligo-3-hexylthiophène et fullerène ont été fonctionnalisés avec des groupements de reconnaissance complémentaires mélamine – acide barbiturique. La présence de élements solubilisants confère à ces composés une bonne mise en oeuvre permettant la fabrication de dispositifs photovoltaïques à hétérojonction volumique. L'effet de la composition et du post-traitement de la couche active sur la performance de ces dispositifs ont été explorés. Les études de mobilité de charge et des mécanismes de recombinaison au sein de ces matériaux indiquent que l'équilibre entre auto-association et séparation de phases est crucial pour l'efficacité en conversion photovoltaïqueThis research aims to elucidate the use of supramolecular interaction to guide the formation of well-defined nanoscale self-assembled architecture in photovoltaic solar cells as a means to improve device efficiency. Complementary molecular recognition sites based on melamine and barbituric acid were used to obtain functionalized fullerene and oligothiophene materials with superior processibility thanks to the presence of specific solubilizing groups. The efficiency of solid-state devices fabricated using the bulk heterojunction design was studied with respect to device morphology and composition. Experiments on recombination mechanism and field effect mobilities suggest that the balance between hydrogen-bonding interactions induce self-assembly and p-p interactions to promote phase segregation is crucial to the micro-structure of the active layer. The investigated of the relationship between the oligothiophene chain size and various complementary hydrogen-bonding motifs is envisaged
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Motaung, David Edmond. "Structure property relationship and thermal stability of organic photovoltaic cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6331_1307942460.
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In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films.
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Stranks, Samuel David. "Investigating carbon nanotube - polymer blends for organic solar cell applications." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:3a65d509-1610-4517-b10d-c90d832134c3.
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This thesis describes studies on nanohybrid systems consisting of single-walled carbon nanotubes (SWNTs) with monolayer coatings of semiconducting polymers. Steady-state and time-resolved optical and high-resolution microscopy experiments were used to investigate the blends. These materials show promise for use in organic photovoltaics (OPVs) owing to the high carrier mobilities and large aspect ratios of SWNTs, the controllable solubilisation of tubes with various polymers and the broad light-harvesting abilities of organic polymers. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising carbon nanotubes in OPV devices, revealing poor performances to date. The experimental methods used during the thesis are detailed in Chapter 3 and the solution processing techniques used to prepare the polymer–nanotube blend samples are described in Chapter 4. Chapter 5 describes a study on a nanotube blend with a thiophene polymer, a system previously unsuccessfully implemented into OPV devices. Ultrafast spectroscopic measurements showed that electrons can transfer on a 400 fs time scale from the polymer to nanotubes and the conditions to allow long-lived free charges to be produced were found. The study is extended in Chapter 6 to show that nanostructures consisting of a nanotube coated in one polymer can then be coated by a second polymer and that these nano-engineered structures could be implemented into OPV devices. The use of a competition binding process to isolate purely semiconducting nanotubes dispersed with any desired polymer is then described in Chapter 7. Finally, Chapter 8 introduces systems consisting of chains of porphyrin units, nature’s light-harvesting systems, bound to nanotubes and the blends were found to exhibit the required electronic alignment for use in OPVs. The work described in this thesis provides an explanation for the poor device behaviour of nanotube–polymer blends to date and, in particular, demonstrates several nanohybrid systems that show particular promise for improved OPV applications.
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Marinado, Tannia. "Photoelectrochemical studies of dye-sensitized solar cells using organic dyes." Doctoral thesis, Stockholm : Skolan för kemivetenskap,Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11248.
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Gordon, Scott W. "Incorporation of Gold Nanowires into Photovoltaic Devices." ScholarWorks@UNO, 2019. https://scholarworks.uno.edu/td/2608.
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To this day, fossil fuels still make up over 80% of the earth’s energy production. Many sources of renewable energy are available, but photovoltaics is the only source with the capacity proven to meet the increasing world energy needs. Third generation devices such as dye-sensitized and organic solar cells have gained much interest due to their cost effectiveness and flexibility but have yet to become commercially viable. Here methods have been studied to improve these devices with the use of Gold nanowire arrays. These additions provide plasmonic and light scattering enhancements in dye-sensitized solar cells. Different TiO2 deposition methods have been studied to protect the gold from the redox couple in the electrolyte. Several novel methods have been undertaken to incorporate gold nanowire arrays in organic solar cells with some success. Structural characterization shows the proposed architecture is achieved, but working devices met suffered from low success rate.
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Huang, Lanqi. "Synthesis and characterization of benzodithiophene- and quinoxalinedithienothiophene-based semiconducting materials for organic solar cells." HKBU Institutional Repository, 2019. https://repository.hkbu.edu.hk/etd_oa/608.
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Organic semiconducting materials have been attracted considerable attention as a promising technology for the next generation flexible electronic devices, such as solar cells and field-effect transistors because of their advantages of low-cost, structural versatility and flexibility. Many organic semiconducting materials have been developed in recent years. In this thesis, four pi-conjugated building blocks based on benzodithiophene and quinoxalinedithienothiophene were applied to develop novel photovoltaic materials, including donor-acceptor alternating copolymers as a donor material for polymer solar cells, photosensitizers for dye sensitized solar cells, small molecule hole transporting materials for perovskite solar cells and small molecule acceptors for organic solar cells. A comprehensive review of current development of organic photovoltaic materials was presented in Chapter 1. In Chapter 2, a series of D-A copolymers (PBB-n) based on 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole and 4,5-bis((2-ethylhexyl)oxy)benzo[2,1-b:3,4-b'] dithiophene attached with different solubilizing side-chains were designed, synthesised and characterized. In general, PBB-n polymers showed good absorption in the region of visible light and UV region, indicating such polymers are a promising light harvester. Also, PBB-n exhibited suitable energy levels, suggesting that they could be applied as the donor materials in polymer solar cells. PBB-n also exhibited various extent of aggregation behaviour. Chapter 3 described syntheses and the fluorination effect of two series of fluoro-substituted PBB-n copolymers, namely PfBB-n and PffBB-n on optical, electrochemical, and optoelectronic properties. Among them, PfBB-n series was characterized with photovoltaic performance. The champion devices fabricated from PfBB-12 showed a PCE as high as 9.7%, with a Voc of 0.92 V, a Jsc of 16.60 mA/cm-2 and a FF of 63.49%. Cells fabricated from other PfBB-n copolymers also exhibited good PV performance with PCE ranging from 7.4 - 8.5%. For PffBB-n polymers, temperature-dependent aggregation behaviour was exploited by modulating the coating temperature during device fabrication. PSC devices based on PffBB-n exhibited good PV performance with PCE ranging from 7.4% to 9.9%. Among which, PffBB-14 provided the most promising PV performance with PCE of 9.9%, a Voc of 0.92 V, a Jsc of 16.8 mA/cm-2 and a FF of 64.36%. Electron deficient conjugated structure was seldom used as the π-bridge in metal-free photosensitizers. In Chapter 4, four novel organic photosensitizers, namely QC5-m and PC5-n were designed with an electron deficient π-bridge. Typical sandwich-structured DSSCs based on the newly developed photosensitizers exhibited promising photovoltaic performance with PCE ranging from 5.23 - 7.77 %, with a maximum Jsc as high as 15.63 mA cm-2. These results suggest that the use of electron deficient π-bridge provides alternative approach to construct efficient organic photosensitizers. Chapter 5 and Chapter 6 described the design, synthesis and investigation of novel hole-transporting materials and electron acceptor materials based on benzo[2,1-b:3,4-b']dithiophene-4,5-dione derived building blocks as potential organic photovoltaic materials for solar cell applications. Keywords: organic photovoltaic materials, photosensitizers, polymer solar cell, electron acceptor, hole-transporting materials.
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Flimel, Karol. "Využití nanomateriálů pro organickou elektroniku a fotovoltaiku." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2011. http://www.nusl.cz/ntk/nusl-216677.
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The study of the new materials potentially usable for organic photovoltaic and electronics are getting very important from the point of ecological and financial view. Organic electronic devices are getting more and more popular and it is only up to us to search for the new ones that are able to improve their physical properties. The aim of this thesis is to search for materials like have been mentioned above which have very good semiconducting properties. Solutions of pure materials and its mixtures with different concentrations of fullerene have been investigated by ultra-violet spectroscopy, classical fluorescence and time resolved spectrometry. Mainly, were studied the influence of the central atom and side substituents for the optical and electronical properties of our materials of interest. With adding fullerene was observed quenching phenomena of the fluorescence, because all these new materials show usually high photoluminescence. Based on the given results, the most suitable materials had been chosen to provide trial of making organic solar cell, and therefore investigated by the mean of electric measurements (direct current).
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Yoo, Seunghyup. "Organic solar cells based on liquid crystalline and polycrystalline thin films." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1246%5F1%5Fm.pdf&type=application/pdf.
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Howells, Calvyn T. "Material and device design for organic photovoltaics." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6810.
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This thesis presents novel materials for photovoltaic conversion. The materials described are solution-processable organic semiconductors and have been used in the fabrication of organic photovoltaic cells (OPVs). The widely used PEDOT:PSS layer was investigated in P3HT and PTB7 photovoltaics. By doping, the efficiencies recorded were amongst the highest reported in the field using a conventional architecture. Two low band-gap BODIPY-based polymers were introduced and shown to have properties favourable for optoelectronics. Photovoltaics consisting solely of the polymers as the active component surpassed the performance expected without the use of an acceptor, indicating ambipolar behaviour, which was verified by charge carrier mobility measurements. When blended with an acceptor, the devices demonstrated a short-circuit current density similar to that of P3HT, a well-studied and successful OPV material. They also revealed a broad spectral response and were shown to operate as photodiodes. Two small molecules containing diketopyrrolopyrrole (DPP) and BODIPY were introduced and characterised. The addition of thiophenes red shifted the absorption but did not result in a sufficient bathochromic shift. Instead, a propensity to aggregate limited the performance. PLQY measurements showed the aggregation to quench luminescence. The study demonstrated the importance of controlling aggregation for efficient devices. Two solution-processable small molecules with a germanium-bridged spiro centre were investigated, and the molecular, electrochemical and optical properties discussed. The small molecule with shorter conjugation length exhibited an interesting packing motif shown to be favourable for charge transport. The mobility measurements were an order of magnitude higher than those reported for sexithiophene, a small molecule analogue, and the same order of magnitude as P3HT. The two-dimensional charge transporting nature of the material was verified with two independent techniques: time of flight (TOF) and organic field-effect transistor (OFET) measurements. The mobility of the material was found to vary with annealing, a result of morphological changes. These were studied with optical, electron and scanning probe microscopies. By controlling the morphology with the implementation of a well-defined annealing method, it was possible to improve the performance of OFETs and planar-heterojunction OPVs. Solution-processed bulk-heterojunction OPVs were fabricated, characterised and optimised with Ge spiro molecules. A PCE similar to that of P3HT, 2.66 %, was achieved for the one, whilst a PCE of 1.60 % was obtained for the other. The results are encouraging, and there is scope for improvement by increasing the overlap between the absorption and solar spectrum, for example.
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Kovacik, Peter. "Vacuum deposition of organic molecules for photovoltaic applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:98461a90-5ae3-4ae3-9245-0f825adafa72.
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Organic photovoltaics have attracted considerable research and commercial interest due to their lightness, mechanical flexibility and low production costs. There are two main approaches for the fabrication of organic solar cells – solution and vacuum processing. The former relies on morphology control in polymer-fullerene blends resulting from natural phase separation in these systems. The latter takes advantage of solvent-free processing allowing highly complex multi-junction architectures similar to inorganic solar cells. This work aims to combine the benefits of both by depositing conjugated polymers using vacuum thermal evaporation. By employing this unconventional approach it aims to enhance the efficiency of organic photovoltaics through increased complexity of the thin-film architecture while improving the nanoscale morphology control of the individual active layers. The thesis explores the vacuum thermal deposition of polythiophenes, mainly poly(3-hexylthiophene) (P3HT) and side-group free poly(thiophene) (PTh). A variety of chemical techniques, such as NMR, FT-IR, GPC, DSC and TGA, are used to examine the effect of heating on chemical structure of the polymers. Optimal processing parameters are identified and related to the resulting thin-film morphology and charge transport properties. Efficient photovoltaic devices based on polythiophene donors and fullerene acceptors are fabricated. Materials science techniques AFM, XRD, SEM, TEM and MicroXAM are used to characterize topography and morphology of the thin films, and UV-Vis, EQE, I-V and C-V measurements relate these to the optical and electronic properties. The results of the study show that polymer side groups have a strong influence on molecular packing and charge extraction in vacuum-deposited polymer thin films. Unlike P3HT, evaporated PTh forms highly crystalline films. This leads to enhanced charge transport properties with hole mobility two orders of magnitude higher than that in P3HT. The effect of molecular order is demonstrated on polymer/fullerene planar heterojunction solar cells. PTh-based devices have significantly better current and recombination characteristics, resulting in improved overall power conversion efficiency (PCE) by 70% as compared to P3HT. This confirms that the chemical structure of the molecule is a crucial parameter in deposition of large organic semiconductors. It is also the first-ever example of vacuum-deposited polymer photovoltaic cell. Next, vacuum co-deposited PTh:C60 bulk heterojunctions with different donor-acceptor compositions are fabricated, and the effect of post-production thermal annealing on their photovoltaic performance and morphology is studied. Co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts. Furthermore, by annealing the devices post-situ the PCE is improved by as much as 80%, achieving performance comparable to previously reported polythiophene and oligothiophene equivalents processed in solution and vacuum, respectively. The enhanced photo-response is a result of favourable morphological development of PTh upon annealing. In contrast to standard vacuum-processed molecular blends, annealing-induced phase separation in PTh:C60 does not lead to the formation of coarse morphology but rather to an incremental improvement of the already established interpenetrated nanoscale network. The morphological response of the evaporated PTh within the blend is further verified to positively differ from that of its small-molecule counterpart sexithiophene. This illustrates the morphological advantage of polymer-fullerene combination over all other vacuum-processable material systems. In conclusion, this processing approach outlines the conceptual path towards the most beneficial combination of solution/polymer- and vacuum-based photovoltaics. It opens up a fabrication method with considerable potential to enhance the efficiency of large-scale organic solar cells production.
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Wu, Zhenghui. "Impact of metal oxide/bulk-heterojunction interface on performance of organic solar cells." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/159.
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Organic photovoltaics have shown much promise as an alternative photovoltaic technology for application in low-cost, large-scale and flexible solar cells. The application of metal oxides in organic solar cells (OSCs) and the impact of the properties of metal oxide/organic hetero-interfaces on cell performance have attracted a lot of attention. The metal oxide/organic interfaces have a crucial impact on interfacial charge transfer, charge collection and the overall device performance. This thesis is aimed at clarifying the principal interfacial phenomena occurring at the metal oxide/organic hetero-interfaces as well as effective engineering of those interfacial properties in OSCs. Photo-generated electrons and holes undergo different recombination processes, e.g., bimolecular recombination and trap-assisted recombination, before being collected by the electrodes in OSCs. Light intensity-dependent current densityvoltage (JV) characteristics of OSCs were analyzed to study the effect of recombination on charge collection efficiency. Effect of metal oxide/organic hetero-interfaces on charge transfers at organic/electrode interface was analyzed using transient photocurrent (TPC) measurements. Light intensity-dependent JV characteristics and TPC characteristics were applied to explore the charge recombination dynamics in OSCs with a metal oxide interlayer. This project concentrated on an in-depth investigation of the physics and the interface phenomena such as interfacial exciton dissociation, charge recombination processes, charge collection and interface engineering for high performing OSCs. The fundamentals about light intensity-dependent J-V characteristics for OSCs were summarized. The relationship between the charge recombination dynamics and light intensity-dependent J-V characteristics in OSCs were developed. Light intensity-dependent JSC, VOC and FF in OSCs made with different bulk-heterojunction (BHJ) systems of PTB7:PC70BM, PTB7-Th:PC70BM and PNB4:PC70BM were investigated. It is found that bimolecular recombination is the most prominent factor limiting the performance of OSCs. For freshly made OSCs fabricated based on the commercial polymers, e.g. PTB7 & PTB7-Th, and the new polymer PNB4 synthesized in-house, the trap-assisted charge recombination process in the BHJ active layer plays a relatively small role. This suggests that reducing the bimolecular recombination in OSCs through selecting proper materials and device structures is crucial for enhancing the power conversion efficiency (PCE) of OCSs. In this work, device structures which enable reducing bimolecular recombination in OSCs were investigated. The effect of ZnO interlayer at the interface between BHJ and Al cathode on the performance of PTB7:PC71BM based OSCs was studied by a combination of theoretical simulation and experimental characterization techniques, e.g., using light intensity-dependent JV characteristic and TPC measurements etc. It shows that ZnO interlayer has a profound effect on the performance of the PTB7:PC70BM-based OSCs, although it does not have a significant influence on the maximum absorptance in the active layer. The origin of the improvement in the cell performance is associated with the efficient charge collection due to the favorable exciton dissociation at the electrode/active layer interface. It is shown that the presence of the ZnO interlayer allows using a thinner active layer without moderating the absorption in the optically optimized control OSCs without the ZnO interlayer. OSCs with a ~10 nm thick ZnO interlayer are found to be favorable for the efficient charge collection, and thereby improving the cell performance. The TPC measurements also reveal that the dissociation of excitons at the metal/organic interface of regular OSCs hinders the electron collection. The unfavorable interfacial exciton dissociation can be removed by interposing a ZnO interlayer at the Al/organic interface, thus bimolecular recombination at the electrode/active layer interface can be reduced for improving the charge collection efficiency. PCE of the OSCs using ZnO interlayer was 6.5%, which is about 20% higher than a control cell (5.4%), having an identical device configuration without a ZnO interlayer. Solution-processed anode interlayer, a mixture of solution-processed MoOX and PEDOT:PSS, was adopted for application in inverted PTB7:PC71BM-based OSCs. The ratio of MoOX to PEDOT:PSS in the mixed solution was optimized for achieving the best cell performance. A PCE of 7.4% was obtained for OSCs with an optimal MoOX-PEDOT:PSS based interlayer, interposed between the BHJ active layer and Ag anode, which means 10% enhancement over the PCE of control cell made with an evaporated MoOX interlayer. Light intensity-dependent JV characteristics implied that the bimolecular recombination in OSCs with a MoOX-PEDOT:PSS interlayer was reduced. TPC measurements showed that the favorable exciton dissociation occurs at the organic/MoOX interface for the inverted OSCs. The favorable interfacial exciton dissociation generates an electrical field within a very small space near the interface, contributing significant additional photocurrent when the effective bias across the active layer in the OSCs is low, and thereby assisting in an efficient charge collection at the organic/electrode interface. In addition to the improvement in the cell performance, the solution-processed MoOX-PEDOT:PSS interlayer does not require a post-annealing treatment, which is beneficial for application in solution-processed tandem and flexible OSCs.
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Weisspfennig, Christian Thomas. "Investigation of charge-transfer dynamics in organic materials for solar cells." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:add81bd2-f953-44ed-b977-d3e15ea4c411.
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This thesis improves our understanding of the charge-transfer dynamics in organic materials employed in dye-sensitized and nanotube-thiophene solar cells. For the purpose of this work, a femtosecond transient absorption spectroscopy setup was built. Additionally, microsecond transient absorption spectroscopy was utilised to explore dynamics on a longer time-scale. In the first study, the dependence of dye regeneration and charge collection on the pore- filling fraction (PFF) in solid-state dye-sensitized solar cells (DSSCs) is investigated. It is shown that while complete hole transfer with PFFs as low as ~30% can be achieved, improvements beyond this PFF are assigned to a stepwise increase in the charge-collection efficiency in agreement with percolation theory. It is further predicted that the chargecollection efficiency saturates at a PFF of ~82%. The study is followed by an investigation of three novel hole-transporting materials for DSSCs with slightly varying HOMO levels to systematically explore the possibility of reducing the loss-in-potential and thus improving the device efficiency. It is shown that despite one new HTM showing a 100% hole-transfer yield, all devices based on the new HTMs performed worse than those incorporating spiro-OMeTAD. Furthermore, it is demonstrated that the design of the HTM has an additional impact on the electronic density of states present at the TiO2 electrode surface, and hence influences not only hole- but also electron-transfer from the sensitizer. Finally, a study on a polymer-single-walled carbon nanotube (SWNT) molecular junction is presented. Results from femtosecond spectroscopic techniques show that the polymer poly(3-hexylthiophene) (P3HT) is able to transfer charges to the SWNT within 430 fs. Addition of excess P3HT polymer leads to long-lived free charges making these materials a viable option for solar cells.
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Aung, Pyie Phyo. "Monte Carlo Simulations of charge Transport in Organic Semiconductors." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1418272111.
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Cabau, Parra Lydia. "Design and Synthesis of Small Molecules for Organic and Grätzel Solar Cells." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/320183.
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El creixement de la població i dels nous països emergents fa que el consum energètic es dispari. Tota la població depèn d’aquest consum i com a conseqüència es depèn de les reserves de combustibles fòssils disponibles.
Una de les fonts d’energia no esgotable i que proveu a la terra d’una gran quantitat d’energia es el Sol. Aquesta Energia ja està sent explotada amb la utilització de panells solars basades en silici. No obstant degut al seu alt cost de fabricació no poden competir amb les fonts d’energia ja existents. Per tant, noves investigacions en alternatives han estat àmpliament estudiades.
Unes de les alternatives que han estat àmpliament estudiades durant aquests anys han estat les cel·les sensitivitzades amb colorant (DSSC) i les cel·les orgàniques (OPV). Les bases i el funcionament d’aquests dos tipus de dispositius es mostren en el capítol 1.
El principal estudi d’aquesta tesis es centra en el disseny i la síntesis de nous colorants per aquest tipus de dispositius. Aquests colorants tenen un paper molt important en aquests dispositius i moltes vegades la seva eficiència deriva de l’estructura d’aquests colorants degut a les reaccions que es produeixen en els dispositius.
En el Capítol 3 i 4 es presenta el disseny de dos tipus de colorants pel que fa a les cel·les sensitivitzades amb colorant (DSSC). En el capítol 3 es tracta de noves molècules orgàniques amb estructura D-π-A àmpliament estudiades com a alternativa als complexes de ruteni. En el capítol 4 les molècules sintetitzades també per DSSC són una família de porfirines, les quals són les que actualment estan mostrant més eficiència.
Per una altra banda en el capítol 5 s’ha sintetitzat també una porfirina però en aquest cas per estudiar la seva aplicabilitat en les cel·les solars orgàniques (OPV).El Crecimiento de la población I de nuevos países emergentes hace que el consume energético se dispare. Toda la población depende de este consume I como consecuencia se depende de las reservas de combustibles fósiles disponibles. Una de las Fuentes de energía no agotable y que suministra a la tierra de una gran cantidad de energía es el Sol. Esta energía ya está siendo explotada con la utilización de paneles solares basados en Silicio. Sin embargo, debido a su elevado coste de fabricación no pueden competir con fuentes de energía ya existentes. Por lo tanto, nuevas investigaciones en alternativas han estado estudiadas. Una de las alternativas que han sido más estudiadas son las Celdas sensitibizadas con colorante (DSSC) i las Celdas Orgánicas (OPV). Las bases y su funcionamiento se muestran en el capítulo 1. El principal estudio de esta tesis se centra en el diseño y la síntesis de nuevos colorantes para estos tipos de dispositivos. Estos colorantes tienen un papel muy importante en estos dispositivos y muchas veces su eficiencia deriva de la estructura del colorante debido a reacciones que se producen en el dispositivo. En el Capítulo 3 y 4 se presenta el diseño de dos tipos de colorantes para las celdas sensitibizadas con colorante. En el Capítulo 3 se muestran moléculas orgánicas con estructura D--A que han sido ampliamente estudiadas como alternativa a los complejos de rutenio. En el capítulo 4 una familia de porfirinas ha sido sintetizada debido a los prometedores resultados mostrados siendo en la actualidad las moléculas que dan más eficiencia. En el Capítulo 5 en cambio se ha sintetizado una porfirina, pero en este caso para estudiar su aplicabilidad en las celdas orgánicas (OPV)
The population is growing and the consumption of energy is dramatically increasing. All the population depends on this energy and are using fossil fuels available. One of this renewable source that gives to the earth a huge amount of energy is the sun. This source is exploited nowadays with photovoltaic devices based in silicon. However due to their high cost of production is not an alternative comparing with the existent sources. For this reason scientists of the entire world are working hard in the development of alternative devices in order to reduce the cost, decrease the contamination and increase the efficiencies among others. Some of alternatives that have been widely studied during the last years have been the Dye Sensitized Solar Cells (DSSC) and Organic Solar Cells (OPV). Basic principles of these devices are showed in Chapter 1. Principally the study of this thesis was focused in the design and synthesis of new sensitizers for these devices. These sensitizers play an important role in these devices and many times their structure depends on the efficiency of the device. In Chapter 3 and 4 the design and synthesis of two kinds of sensitizers and their applicability in DSSC is showed. In chapter 3 the sensitizers are organic dyes with a structure of D-π-A widely studied as alternative to the ruthenium complexes. In chapter 4 another family of sensitizers have been synthesized and also their applicability in DSSC has been studied. In this chapter the molecules are a family of porphyrins that are the molecules that nowadays are showing the most efficiency. On the other hand in Chapter 5 a new porphyrin has been synthesized but in this case to study their applicability in Organic solar Cells (OPV)
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Park, Yoonseok. "Light trapping substrates and electrodes for flexible organic photovoltaics." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-219686.
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Organic solar cells are one of the most promising candidates for future solar power generation. They are thin and lightweight with several additional advantages such as scalability, environmental sustainability and low cost for processing and installation. However, the low charge carrier mobility of the absorbing material for organic solar cells requires thin absorber layers, limiting photon harvesting and the overall power conversion efficiency. Several attempts, e.g., periodically patterned structures and scattering layers have been tried to enhance the absorption of thin-film solar cells as light trapping elements. However, much effort is required to introduce light trapping structures to conventional rigid metal oxide electrodes and glass substrate. For instance, almost 13 hours are required to fabricate micro structures of 1 m2 area on glass, in contrast, 1 minute on PET using a same laser set-up and an additional scattering layers are demanded for providing light trapping effects to solar cells. In the last years, flexibility is emerging as the one of the major advantages of organic solar cells. To realize flexibility of solar cells, the classically used glass substrates and ITO electrodes are too brittle. Therefore, polymer materials are promising candidates to replace them as flexible electrodes and substrates. In this thesis, the highly transparent conducting polymer, PEDOT:PSS and PET equipped with an AlOx encapsulation layer are used as electrode and substrate, respectively. Besides the flexibility, additional light trapping elements, e.g. scattering particles, nano- and microstructures can be easily applied to the polymer materials since they have the potential for easier shaping and processing. In this study, we apply different light trapping and in-coupling approaches to organic solar cells. First, PET substrates are structured with a direct laser interference patterning system, which is a powerful and scalable one-step technique for patterning polymers. Almost 80 % of the light is diffracted by these patterned PET substrates and thereby the light path in the absorption layer is increased. Optical display films, commercially developed to be used as back light units of liquid crystal displays are also examined as light trapping substrates and exhibit similar enhancement as patterned PET. Moreover, since PEDOT:PSS is prepared by a solution-based process, TiO2 nanoparticles are added as light scattering elements to the PEDOT:PSS electrodes. Consequently, those electrodes provide a dual function as electrical contact and light trapping element. Finally, 2- or 3-dimensional nanostructures are printed by a nano-imprinting technique onto the surface of PEDOT:PSS with PDMS stamps. By controlling the temperature and the time of PEDOT:PSS during an annealing step, nanostructures are transferred from PDMS masks to PEDOT:PSS. To evaluate the effects of light trapping for all above mentioned approaches, flexible organic solar cells are produced by vacuum evaporation using blends of DCV5T-Me and C60 as absorber layer. The substrates are optically characterized using UV-vis spectrometer and goniometer measurements. The topography of the samples is measured by atomic force microscopy, scanning microscopy and optical microscopy. Bending tests with various radii are performed to test the flexibility of the substrates. In summary, light trapping effects are successfully implemented in the electrodes and substrates for OPVs, giving efficiency improvements of up to 16 %. The light trapping mechanisms in our approaches are extensively discussed in this thesisOrganische Photovoltaik ist einer der vielversprechendsten Kandidaten für die zukünftige Solarstromgewinnung auf flexiblen Substraten. Um diese Flexibilität zu ermöglichen, sind herkömliche Glassubstrate mit ITO-Elektroden zu spröde. Ein vielversprechender Kandidat, um sowohl flexible Elektroden als auch flexible Substrate herzustellen, sind Polymere, da diese sehr biegsam und leicht zu verarbeiten sind. Deshalb wird in dieser Arbeit das hoch transparente, leitfähige Polymer PEDOT:PSS als Elektrode und PET (mit einer AlOx Verkapselungsschicht) als Substrat untersucht. Aufgrund der guten Prozessierbarkeit der Polymere konnten wir zusätzlich zu den eigentlichen Funktionen des Substrates und der Elektrode noch den Mechanismus des Lichteinfangs hinzufügen. Zusätzlich zu ihrer Flexibilität haben organische Solarzellen noch weitere Vorteile: sie sind dünn, leicht, skalierbar und verursachen vergleichsweise geringe Kosten für Herstellung und Installation. Ein Nachteil organischer Solarzellen ist die vergleichsweise geringe Ladungsträgerbeweglichkeit der Absorbermaterialien, welche oft die Schichtdicke der Absorbermaterialien begrenzt. Dies hat weniger absorbierte Photonen, weniger Stromdichte und somit einen geringeren Wirkungsgrad zur Folge. In den letzten Jahren wurden periodisch strukturierte Substrate und streuende Schichten als Lichteinfangelemente eingesetzt, um den Wirkungsgrad organischer Solarzellen mit dünnen Absorberschichten zu erhöhen. Gestaltungsregeln für solche Lichteinfangelemente sind noch weitestgehend unbekannt. Im Rahmen dieser Arbeit strukturieren wir PET Substrate mit einem direkten Laserinterferenzsystem, welches ein leistungsfähiges, skalierbares Einschrittverfahren zur Polymerstrukturierung ist. Da PEDOT:PSS aus der Lösung prozessiert wird, können wir weiterhin Nanopartikel hinzufügen, die der Elektrode zusätzlich noch lichtstreuende Eigenschaften geben. Außerdem können 2- bzw. 3-dimensionale Nanostrukturen leicht mithilfe einer Stempeltechnik eingeprägt werden. Um die Effekte des Lichteinfangs, welcher durch die oben genannten Methoden erzeugt wird, zu untersuchen, werden flexible organische Solarzellen mittels Vakuumverdampfung prozessiert. DCV5T-Me und C60 bilden dabei die photoaktive Schicht. Somit werden die Licht fangenden Eigenschaften dieser flexiblen Solarzellen ausgenutzt und ausführlich in der Arbeit diskutiert
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Tant, Julien. "Discotic liquid crystals as organic semiconductors for photovoltaic device applications." Doctoral thesis, Universite Libre de Bruxelles, 2004. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211134.
Full textAbstract:
Les sources d'énergie renouvelable connaissent un essor grandissant. Parmi celles-ci se trouvent les cellules photovoltaïques. Elles ont pour objet la transformation de la lumière en électricité. Les dispositifs actuels, basés sur le silicium, nécessitent des matériaux de très grande pureté et de hautes températures de mise en œuvre, les empêchant de concurrencer les principales sources d’énergie actuelles (fossile, nucléaire).Une alternative pourrait provenir des matériaux semi-conducteurs organiques. En effet, l’utilisation de méthodes de mise en œuvre à partir de solutions pourrait permettre la fabrication de dispositifs flexibles et bon marché. Des résultats encourageants ont été obtenus avec des polymères conjugués et de petites molécules organiques. Les cristaux liquides discotiques CLDs forment une catégorie particulièrement intéressante de matériaux. Ils ont en effet la capacité de s’organiser spontanément en colonnes de molécules, formant des semi-conducteurs à une dimension. Leurs propriétés intéressantes en tant que semi-conducteurs, combinées à une mise en œuvre facile, en font de bons candidats pour de futures applications.
Dans ce travail, deux familles complémentaires de matériaux discotiques ont été développées, formant une paire de semi-conducteurs de type n et p. Leurs structures chimiques ont été étudiées en vue d'obtenir des matériaux possédant un ensemble de propriétés choisies afin d’optimiser les paramètres clefs du processus de photo-génération de charges. Ces propriétés sont les suivantes: forte absorption de la lumière dans le visible, fort caractère semi-conducteur de type n ou p, pas de phase cristalline à température ambiante, présence d'une phase cristal liquide colonne, phase isotrope en dessous de 200°C. De plus, les matériaux doivent être accessibles en un nombre minimum d’étapes d’une synthèse efficace, et ce avec un haut niveau de pureté. Ils doivent également être fortement solubles dans les solvants organiques usuels.
Cette étude comporte, pour chacune des deux familles de matériaux, le design de leur structure chimique, leur synthèse et la caractérisation de leurs propriétés physiques (thermotropes, optoélectroniques, électrochimiques). Comme possible semi-conducteur de type p, cinq dérivés tétrasubstitués de la phthalocyanine non-métallée ont été synthétisés, donnant un matériau possédant l’ensemble des propriétés recherchées. Comme possible semi-conducteur de type n, six dérivés hexasubstitués de l’hexaazatrinaphthylène ont été étudiés. L’un d’eux possède les propriétés requises.
Finalement, les propriétés optoélectroniques et photovoltaïques de mélanges des deux matériaux les plus prometteurs, ensemble ou avec d’autres matériaux, ont été étudiées. Des cellules solaires de rendement maximum de 1 % ont été obtenues pour deux dispositifs de compositions différentes.
Ces rendements, bien qu’inférieurs à ceux obtenus précédemment par d’autres groupes (jusqu’à 34 % à ce jour), sont néanmoins révélateurs des potentialités des matériaux organiques, et plus particulièrement des cristaux liquides discotiques, pour de futures applications dans le domaine des dispositifs électroniques.
Doctorat en sciences, Spécialisation chimie
info:eu-repo/semantics/nonPublished
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Schulze, Kerstin. "Untersuchungen an Quinquethiophenen zur Verwendung als Donator in Organischen Solarzellen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1224676272024-23808.
Full textAbstract:
Organische Photovoltaik könnte zukünftig eine Möglichkeit zur Energiegewinnung aus erneuerbaren Energiequellen darstellen. Der Vorteil besteht hier vor allen Dingen in dem Potential einer sehr kostengünstigen Herstellung, zum Beispiel einer Produktion im Rolle-zu-Rolle-Verfahren, welche so auf flexiblen Substraten wie beispielsweise Folien erfolgen kann. Obwohl die Materialkosten gering sind, ist bis zu einer Kommerzialisierung Organischer Solarzellen unter anderem eine Erhöhung ihrer Leistungseffizienz notwendig. Vorzugsweise sollten in Organischen Solarzellen Donator- und Akzeptormaterialien verwendet werden, deren Absorptionsspektren und Energieniveaus ideal aufeinander abgestimmt sind, da so zum Beispiel hohe Leerlaufspannungen erreicht werden können. Zusätzlich können hohe Absorptionskoeffizienten der Materialien über einen großen spektralen Bereich zu hohen Stromdichten in diesen photovoltaischen Bauelementen führen. In dieser Arbeit werden neuartige Quinquethiophene als Donatormaterial in Organischen Solarzellen untersucht, welche als Grundeinheit aus fünf Thiophenringen sowie Dicyanovinylendgruppen und Alkylseitenketten bestehen. Die untersuchten Materialien besitzen einen hohen Absorptionskoeffizienten und erreichten auf Grund des hohen Ionisationspotentials hohe Leerlaufspannungen in Organischen Solarzellen unter Verwendung des Fullerens C60 als Akzeptor. Gleichzeitig tritt eine effiziente Trennung der Exzitonen an der Akzeptor-Donator-Grenzfläche auf. Jedoch stellt das hohe Ionisationspotential der Quinquethiophene spezielle Anforderungen an die weitere Solarzellenstruktur. Innerhalb dieser Arbeit wird gezeigt, dass ein Unterschied von eingebauter Spannung und Leerlaufspannung die Form der Solarzellen-Kennlinie entscheidend beeinflusst und eine S-Form in der Nähe der Leerlaufspannung erzeugen kann. Die eingebaute Spannung wird hierbei durch die Kontaktierung der photoaktiven Schichten bestimmt. Eine Erhöhung der eingebauten Spannung der Solarzelle kann durch eine entsprechende Materialwahl erreicht werden. So wird in dieser Arbeit gezeigt, dass Organische Solarzellen basierend auf diesen Quinquethiophenen ohne energetische Barrieren für freie Ladungsträger innerhalb des Bauelements keine S-Form der Kennlinie aufweisen. Ebenfalls wird der Einfluss der unterschiedlichen Quinquethiophenderivate auf die Solarzellen-Charakteristik untersucht. Hierbei wird gezeigt, dass die Länge der Alkylseitenketten einen Einfluss auf die Löcherinjektion sowie die Löcherbeweglichkeit auf dem Oligothiophen hat, welches unter anderem auch die Form der Strom-Spannungs-Kennlinie beeinflusst. Abschließend wird die Möglichkeit der Verwendung dieser Materialklasse in Tandemsolarzellen gezeigt sowie der Vergleich von zwei unterschiedlichen Anodenmaterialien, beides wichtige Aspekte für eine kommerzielle Umsetzung.
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Uhrich, Christian. "Strategien zur Optimierung organischer Solarzellen: Dotierte Transportschichten und neuartige Oligothiophene mit reduzierter Bandlücke." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1209113927393-76737.
Full textAbstract:
Organische Solarzellen besitzen das Potential für leichte und zugleich flexible photovoltaische Anwendungen, die kostengünstig hergestellt werden können und damit einen Beitrag zur Verminderung der Emission von Kohlendioxid, Methan und Stickoxiden leisten können. Zur Herstellung von organischen Solarzellen werden nur geringe Mengen der organischen Materialien benötigt und die Prozessierung findet bei vergleichsweise geringen Temperaturen statt, was die Abscheidung auf z. B. Plastikfolie ermöglicht. Man unterscheidet drei Arten von organischen Solarzellen. Erstens, Solarzellen bestehend aus kleinen Molekülen, die im Vakuum durch Sublimation auf das Substrat abgeschieden werden. Zweitens, Polymersolarzellen, deren Schichten aus Lösung meist durch „spin-coating“ oder Druckverfahren präpariert werden. Und drittens, „dye-sensitized“ Solarzellen (auch Grätzel-Zellen), die aus einer porösen Schicht Titandioxid und einem flüssigen Elektrolyten für den Ladungsträgertransport bestehen. Diese Arbeit beschäftigt sich ausschließlich mit organischen Solarzellen aus kleinen Molekülen. Die höchsten erreichten Wirkungsgrade organischer Solarzellen aus kleinen Molekülen liegen derzeit bei etwa 5 % . Um die Effizienzen von Solarzellen aus kleinen Molekülen zu steigern, ist es einerseits notwendig das Verständnis der physikalischen und chemischen Prozesse innerhalb der Bauelemente genauer beschreiben zu können, andererseits werden neue Materialien mit optimierten Eigenschaften für die organische Photovoltaik benötigt. In dieser Arbeit wurden zwei Strategien zur Optimierung organischer Solarzellen verfolgt: • Durch die Optimierung des Versatzes der Energieniveaus der organischen Materialien konnte die Leerlaufspannung in einem Modellsystem maximiert werden. An diesem Modellsystem wurden der Ursprung der Leerlaufspannung und die Rekombinationsdynamik von photogenerierten Ladungsträgern untersucht. Bezüglich der Leerlaufspannung zeigen Solarzellen, deren photoaktive Materialien in einer Mischschicht vorliegen, im Vergleich zu Solarzellen, die eine photoaktive Doppelschicht beinhalten, fundamentale Unterschiede . • Des Weiteren wurden neue Thiophenderivate untersucht, die als aktive Materialien in organischen Solarzellen eingesetzt wurden. Durch elektronenziehende Endgruppen wurde das Ionisationspotential der Thiophenderivate abgesenkt und die optische Bandlücke verringert. Das Thiophenderivat DCV3T fungiert in Kombination mit herkömmlichen Donator-Materialien als Akzeptor. In Mischschichten aus DCV3T und C60 kommt es durch einen Hin- und Rücktransfer der Anregungsenergie zwischen den Materialien statt der Generation von freien Ladungsträgern zu einer Erhöhung der Triplett-Exzitonendichte auf DCV3T . Diese Exzitonen besitzen auf Grund der hohen Lebensdauer von Triplett-Exzitonen das Potential für eine erhöhte Exzitonendiffusionslänge, die in einem neuen Solarzellenkonzept ausgenutzt werden konnteOrganic solar cells have the potential for light weight and flexible applications. They can be manufactured cost-effectively and can thus contribute to the reduction of the emission of carbon dioxide, methane and nitric oxides. In order to manufacture organic solar cells, only small amounts of organic materials are required. They can be processed at comparably low temperatures. Therefore, the fabrication on substrates like plastic foil is possible. Three different types of organic solar cells exist. The first kinds are solar cells prepared from small molecules that are manufactured via sublimation of the material in a vacuum. The second kind are polymer solar cells manufactured from solution by spin coating techniques or ink jet printing. And thirdly, dye sensitized solar cells - also known as Grätzel cells - consisting of a porous layer of titanium dioxide and most commonly a liquid electrolyte for the charge transport. This work deals exclusively with small molecule solar cells. The highest power conversion efficiencies reached by small molecule organic photovoltaics are now in the range of 5 %. In order to increase the efficiencies of solar cells prepared from small molecules, two major aspects must be developed. The understanding of the physical processes within the organic devices must be improved. And secondly, new materials are required with physical properties optimized for organic photovoltaics. In this work, I followed two strategies for optimizing organic solar cells: • By optimizing the offset of energy levels between donor and acceptor material, the open circuit voltage could be increased. In the investigated model system, the origin of the open circuit voltage and the recombination dynamics of photo generated charge carriers were analyzed. Concerning the open circuit voltage, solar cells consisting of a donor acceptor double layer structure, show fundamental differences to solar cells consisting of a donor acceptor blend. • Furthermore, new thiophene derivatives used as photoactive materials were investigated. By the attachment of electron withdrawing end groups, the ionization potential of the oligothiophenes is increased and the optical band gap is reduced at the same time. The investigated thiophene derivative DCV3T acts as an acceptor in combination with the commonly used donor-materials. A back- and forth-transfer of excitation energy is observed in blends of DCV3T and fullerene C60. In these blends, excitons are not separated into free charge carriers. This back and forth transfer leads to an enhancement of the density of triplet excitons on DCV3T. These excitons have a potentially high diffusion length due to the long lifetime of triplet excitons. This effect was utilized in the organic solar cells
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Al, Kadi Jazairli Mohamad. "Growth of Zinc Oxide Nanoparticles on Top of Polymers and Organic Small Molecules as a Transparent Cathode in Tandem Photovoltaic Device." Thesis, Linköping University, Department of Science and Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11391.
Full textAbstract:
Organic solar cells have caught considerable attention in the past few years due to their potential for providing environmentally safe, flexible, lightweight, inexpensive, and roll-to-roll feasible production solar cells. However, the efficiency achieved in current organic solar cells is quite low, yet quick and successive improvements render it as a promising alternative. A hopeful approach to improve the efficiency is by exploiting the tandem concept which consists of stacking two or more organic solar cells in series.
One important constituent in tandem solar cells is the middle electrode layer which is transparent and functions as a cathode for the first cell and an anode for the second cell. Most studies done so far have employed noble metals such as gold or silver as the middle electrode layer; however, they suffered from several shortcomings especially with respect to reproducibility.
This thesis focuses on studying a new trend which employs an oxide material based on nano-particles as a transparent cathode (such as Zinc-oxide-nano-particles) along with a transparent anode so as to replace the middle electrode.
Thus, this work presents a study on solution processable zinc oxide (ZnO) nanostructures, their proper handling techniques, and their potential as a middle electrode material in Tandem solar cells in many different configurations involving both polymer and small molecule materials. Moreover, the ZnO-np potential as a candidate for acceptor material is also investigated.
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Bolognesi, Margherita. "Organic bulk-heterojunction photovoltaic devices: materials, device architectures and interfacial processes." Doctoral thesis, Universitat Rovira i Virgili, 2013. http://hdl.handle.net/10803/128202.
Full textAbstract:
Research on organic photovoltaic devices (OPV) has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. Thanks to the indtroduction of the bulk heterojunction (BHJ) concept, today BHJ OPV efficiencies are exceeding 9%. This thesis gives an overview on the different possible strategies that could be adopted for a further. improvement of BHJ OPV devices performances. The accurate analysis of the chemical, energetic and physical criteria governing the solar cells functioning allowed to individuate some critical aspects and apply possible solutions by a fine tuning of the materials chemical structures, device processing techniques and device architecture engineering. Even though noit in all cases the applied strategy successfully led to device efficiency improvements, the fundamental understanding of some of the efficiency limiting factors could serve as useful scientific basis for future developments.