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Kondo, Takeshi. "Current-voltage characteristics of organic semiconductors interfacial control between organic layers and electrodes /." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-05022007-122219/.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.Dr. Marder Seth R, Committee Chair ; Dr. Kippelen Bernard, Committee Co-Chair ; Dr. Brďas Jean-Luc E, Committee Member ; Dr. Perry Joseph W, Committee Member ; Dr. Srinivasarao Mohan, Committee Member.
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Bittle, Emily Geraldine. "Voltage Modulated Infrared Reflectance Study of Soluble Organic Semiconductors in Thin Film Transistors." UKnowledge, 2013. http://uknowledge.uky.edu/physastron_etds/10.
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Soluble organic semiconductors have attracted interest due to their potential in making flexible and cheap electronics. Though their use is being implemented in electronics today, the conduction mechanism is still under investigation. In order to study the charge transport, this study examines the position, voltage, and frequency dependence of charge induced changes in far infrared absorption in soluble organic semiconductors in thin-film transistor structures. Measurements are compared to a simple model of a one-dimensional conductor which gives insight into the charge distribution and timing in devices. Main results of the study are dynamic measurements of charge taken by varying the frequency of the applied gate voltage while observing signal at one position within the transistor; mobility values obtained from a comparison to the one-dimensional model compare well with standard current-voltage measurements. Two small molecule soluble organic semiconductors were studied: 6,13 bis(triisopropylsilylethynyl)-pentacene and fluorinated 5,11 bis(triethylsilylethynyl) anthradithiophene.
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Widmer, Johannes. "Charge transport and energy levels in organic semiconductors." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-154918.
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Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devicesOrganische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile
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Naresh, Shakya Man. "Studies of Electronic Transport in Novel Smectic and Discotic Liquid Crystalline Organic Semiconductors." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1289418142.
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Pejic, Sandra. "Structure-Property Studies of Substituted Azadipyrromethene-Based Dyes and High Dielectric Constant Polymers for Organic Electronic Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1527949734211196.
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Schott, Sam. "Spin dynamics in organic semiconductors." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288119.
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Organic semiconductors exhibit exceptionally long spin lifetimes, and recent observations of the inverse spin hall effect as well as micrometer spin diffusion lengths in conjugated polymers have spiked interest in employing such carbon-based materials in spintronics applications. The charge transport and photophysics of organic semiconductors have been intensely studied for optoelectronic applications, revealing subtle relationships between molecular geometry, morphology and physical properties. Similar structure-property relationships remain mostly unknown for spin dynamics, where the charge carrier spins couple to their environment through hyperfine (HFI) and spin-orbit interactions (SOC). HFIs provide a pathway for spin relaxation while SOC plays a dual role in such materials: it couples the spin to its angular momentum and therefore enables both spin-to-charge conversion and spin relaxation. Understanding the molecular SOC, and finding a means to tune its strength, therefore is fundamentally important for materials design and selection. However, quantifying SOC strengths indirectly through spin relaxation effects has proven difficult due to competing relaxation mechanisms. We initially present a systematic study of the g-tensor shift in molecular semiconductors and establish it as a probe for the SOC strength in a series of high mobility molecular semiconductors. The results demonstrate a rich variability of molecular g-shifts with the effective SOC, depending on subtle aspects of molecular composition and structure. We then correlate the above g-shifts to spin-lattice relaxation times over four orders of magnitude, from 200 µs to 0.15 µs, for isolated molecules in solution and relate our findings to the spin relaxation mechanisms that are likely to be relevant in solid state systems. Isolated molecules provide an ideal model system to investigate a spin's interactions with its environment but device applications commonly employ thin films. The second half of this thesis investigates polaron spin lifetimes in field effect transistors with high-mobility conjugated polymers as active layers. We use field-induced electron spin resonance measurements to demonstrate that spin relaxation is governed by the charges' hopping motion at low temperatures while Elliott-Yafet-like relaxation due to short-range, rapid spin density dynamics likely dominates high temperature spin lifetimes. Such a microscopic relaxation mechanism is highly sensitive to the local conformation of polymer backbones and we show its dependence on the degree of crystallinity in a polymer film.
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Park, Duke H. "Theoretical studies of submicron gate length high electron mobility transistors." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/13744.
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Risko, Chad Michael. "Theoretical Evaluations of Electron-Transfer Processes in Organic Semiconductors." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7272.
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The field of organic electronics, in which -conjugated, organic molecules and polymers are used as the active components (e.g., semiconductor, light emitter/harvester, etc.), has lead to a number a number of key technological developments that have been founded within fundamental research disciplines. In the Dissertation that follows, the research involves the use of quantum-chemical techniques to elucidate fundamental aspects of both intermolecular and intramolecular electron-transfer processes in organic, -conjugated molecules. The Dissertation begins with an introduction and brief review of organic molecular systems used as electron-transport semiconducting materials in device applications and/or in the fundamental studies of intramolecular mixed-valence processes. This introductory material is then followed by a brief review of the electronic-structure methods (e.g., Hartree-Fock theory and Density Functional Theory) and electron-transfer theory (i.e., semiclassical Marcus theory) employed throughout the investigations.
The next three Chapters deal with investigations related to the characterization of non-rigid, -conjugated molecular systems that have amorphous solid-state properties used as the electron-transport layer in organic electronic and optoelectronic devices. Chapters 3 and 4 involve studies of silole- (silacyclopentadiene)-based materials that possess attractive electronic and optical properties in the solid state. Chapter 5 offers a preliminary study of dioxaborine-based molecular structures as electron-transport systems.
In Chapters 6 8, the focus of the work shifts to investigations of organic mixed-valence systems. Chapter 6 centers on the examination of tetraanisylarylenediamine systems where the inter-redox site distances are approximately equal throughout the series. Chapter 7 examines the bridge-length dependence of the geometric structure, charge-(de)localization, and electronic coupling for a series of vinylene- and phenylene-vinylene-bridged bis-dianisylamines. In Chapter 8, the role of symmetric vibrations in the delocalization of the excess charge is studied in a dioxaborine radical-anion and a series of radical-cation bridged-bisdimethylamines. Finally, Chapter 9 provides a synopsis of the work and goals for future consideration.
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Chen, Danti. "Local electron transport of organic semiconducting monolayers /." Connect to online version, 2009. http://ada.mtholyoke.edu/setr/websrc/pdfs/www/2009/363.pdf.
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Strobel, Thomas. "High sensitivity infrared charge modulation spectroscopy of high-mobility organic semiconductors." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709322.
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Chu, Rongming. "AlGaN-GaN single- and double-channel high electron mobility transistors /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20CHU.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 74-82). Also available in electronic version. Access restricted to campus users.
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Ravindran, Vinod. "Design and fabrication of boron-containing III-nitrides based high electron mobility transistors." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47606.
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GaN-based HEMTs are among the most promising candidates for high-power and high-frequency applications; a niche for millimeter-wave technologies. Nitride materials indeed outperform other mainstream III-V materials (InP or GaAs) because of several properties, including wider bandgaps, high peak and saturation velocities, large breakdown voltages, together with good thermal conductivities. Nonetheless, the state-of-the-art of nitrides is not yet industrially mature to exploit the entire millimeter-wave range.
A way to push further performance is to develop innovative designs, notably by exploring novel materials. The purpose of this research was therefore to investigate the use of boron-containing III-nitrides in high electron mobility transistors (HEMTs).
The study was first conducted theoretically, through solving the Schrodinger-Poisson equation. Key parameters and relevant equations were derived to implement BGaN materials in our simulations. A GaN/ultrathin-BGaN/GaN heterojunction was showed to provide an electrostatic barrier to electrons and to improve the confinement of the two-dimensional electron gas. GaN back-barrier layers happen to limit leakage in the GaN buffer thanks to two effects: (i) a polarization-induced band discontinuity and (ii) a resistive barrier originating from excellent insulation properties of BGaN.
The study was then, experimentally, several growth campaigns were carried out that led to the fabrication of devices. First, we confirmed the key characteristics of BGaN materials by electrical and optical measurements. Second, we demonstrated the evidence of a significant enhancement of performance of standard AlGaN/GaN structures by the introduction of a BGaN layer in the buffer layer.
Compared to conventional AlGaN/GaN HEMTs, structures grown with BGaN back-barriers showed a significant improvement of static performances, transport properties, and trapping effects involving a limited current collapse in dynamic regime.
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Harkin, David. "Fluorescence enhancement strategies for polymer semiconductors." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267904.
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One of the major challenges in the field of organic semiconductors is to develop molecular design rules and processing routes which optimise the charge carrier mobility, whilst independently controlling the radiative and non-radiative processes. To date there has existed a seeming trade-off between charge carrier mobility and photoluminescence efficiency, which limits the development of some devices such as electrically pumped laser diodes. This thesis investigates fluorescence enhancement strategies for high-mobility polymer semiconductor systems and the mechanisms by which they currently display poor emission properties. Four independent approaches were taken and are detailed as follows. 1. Solubilising chain engineering It is shown that for the high mobility polymer poly(indacenodithiophene-co-benzothiadiazole), the addition of a phenyl- initiated side chain can enhance the solid-state fluorescence quantum yield, exciton lifetime and exciton diffusion length significantly in comparison to that without phenyl-addition. 2. Energy transfer to a highly fluorescent chromophore It is shown that for the high mobility polymer poly(indacenodithiophene-co-benzothiadiazole) efficient energy transfer to a more emissive squaraine dye molecule is possible despite fast non-radiative decay short exciton diffusion lengths. This results in a significant fluorescence enhancement, which in turn facilitates an order of magnitude increase of the efficiency of polymer light emitting diodes made from this material combination. 3. Energy gap engineering The well known Energy Gap Law predicts an increase in the non-radiative rate as the optical bandgap of an organic chromophore decreases in energy. In combination with this, almost all polymer semiconductors reported to date with high charge carrier mobility have low optical bandgaps. Therefore, molecular design principles which act to increase the optical bandgap of polymer semiconductors whilst retaining a high mobility were sought out. One specific system was successfully identified and showed a significant fluorescence enhancement compared to is predecessor poly(indacenodithiophene-co-benzothiadiazole) in both the solution and the solid state. It is found that the Frenkel exciton lifetime in this new system is a factor of four larger which also results in a significantly increased exciton diffusion length. An inter-chain electronic state is also identified and discussed. 4. Hydrogen substitution For some low-bandgap material systems such as erbium chromophores, high energy vibrational modes such as the C-H stretching mode can act as non-radiative pathways. The effect of hydrogen substitution with deuterium and fluorine was therefore investigated in a series of polythiophene derivative families. It was found that in the solid state, fluorescence and exciton lifetime enhancement occurred when the backbone hydrogen atoms were replaced with fluorine. However, evidence is given that this was not owing to the initial hypothesis, and is more likely owing to structural differences which occur in these substituted material systems.
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Weiss, Leah Rachel. "Spin-sensitive probes of triplet excitons in organic semiconductors." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/286356.
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Spin interactions play a key role in the function of molecular materials from naturally occurring biological complexes to synthetic materials for light-harvesting and light-emission. This thesis investigates the spin interactions of spin-1 triplet excitons formed by singlet fission. Singlet fission produces two triplet excitons from one light-induced singlet state and holds promise to enable solar energy generation beyond traditional efficiency limits. As the lifetime of triplet pairs depends sensitively on their spin degree of freedom, in this thesis we deploy spin-sensitive techniques to understand the interactions and evolution of triplet pairs. After introducing the relevant theoretical and experimental background underlying singlet fission and the role of spin, we describe the first observation of strongly exchange coupled, high-spin triplet-pair states ($S=2$) in a solid-state organic semiconductor and show that the singlet fission process allows for the formation of long-lived, strongly coupled spin-two states. We then describe the development and use of photoluminescence-detected avoided level-crossings in applied magnetic fields to quantify the strength of exchange coupling and identify specific optical signatures of exchange-coupled triplet pairs. Using high magnetic fields ($\leq\mbox{60 T}$) we isolate and measure the exchange coupling and optical signatures of multiple distinct triplet pairs in the same material. Finally, we probe the mechanisms of formation and decay of spin polarization from triplet pair states using pulsed spin resonance. The measured dynamics are consistent with polarization driven by fluctuations in exchange coupling between pairs and spin-orbit mediated decay of triplet excitons to the ground state. The combined measurements of the spin parameters and polarization dynamics of triplet pairs from ns to ms timescales provides a quantitative picture of the spin states generated by singlet fission.
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Triplett, Gregory Edward Jr. "Process modeling of InAs/AISb materials for high electron mobility transisitors grown by molecular beam epitaxy." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/9458.
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Montero, Martín Jose María. "Charge transport in organic semiconductors with application to optoelectronic devices." Doctoral thesis, Universitat Jaume I, 2010. http://hdl.handle.net/10803/10474.
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El estudio del transporte de carga en semiconductores orgánicos contribuye al desarrollo y optimización de LEDs orgánicos y nuevas células solares. En OLEDs de un sólo portador se ha encontrado una fórmula explícita de la característica densidad de corriente y potencial (J-V) con movilidad dependiente del campo eléctrico. Un test para diferenciar la movilidad dependiente del campo y de la densidad ha sido dado por medio de una ley universal de escalado. Los espectros de capacidad y los tiempos de tránsito han sido examinados con la inclusión de la movilidad dependiente del campo eléctrico y comparado con los datos experimentales, verificándose el modelo teórico planteado. Se ha descrito la movilidad de portadores de carga a través de un modelo de transporte con una densidad exponencial de trampas. Se han utilizado técnicas de espectroscopía de impedancia para explicar la movilidad dependiente del campo eléctrico en términos del múltiple atrapamiento ejercido por los estados energéticamente localizados. Este modelo ha explicado de forma coherente los espectros de capacidad recogidos en medidas experimentales, particularmente su comportamiento a bajas e intermedias frecuencias. La respuesta de los OLED (polímero SY) ha sido estudiada en los regímenes estacionario y transitorio. En el régimen estacionario, se han descrito las corrientes de fuga a bajos potenciales. Se ha
analizado la existencia de mayor corriente circulando por el perímetro que por el área del dispositivo. En el régimen transitorio, se ha
proporcionado una explicación sobre las colas de luz emitida observadas al cesar la perturbación de potencial escalón: procede de la inyección
limitada de electrones en el cátodo.
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Willis, Maureen. "Muon spin relaxation as a probe of electron spin relaxation in organic semiconductors." Thesis, Queen Mary, University of London, 2012. http://qmro.qmul.ac.uk/xmlui/handle/123456789/5392.
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The purpose of this thesis is to study the electron spin relaxation (eSR) in small organic molecular semiconductors using the muon spin relaxation (MuSR) technique. One of the inherent problems in utilising the spin degree of freedom is the lack of understanding of the fundamental mechanisms behind spin relaxation. Two interactions have been proposed as the dominant mechanisms behind the spin relaxation, the Hyper ne interaction (HFI) and the Spin Orbit (SO) interaction. There remains much debate over the models for these interactions and their exact role, a contention that drives the work carried out in this thesis. The MuSR technique is utilised providing a novel molecular scale probe sensitive to relaxation rates in the range of 0.01-10 MHz. The Avoided Level crossing (ALC) MuSR application is useful in accessing the spin relaxation information. Temperature dependent ALC-MuSR measurements are performed for a selection of functionalised acenes and Quinolate molecules. Transverse eld MuSR measurements are also taken to determine the Hyper ne coupling constants present. DFT and semi-empirical computational methods are employed to determine theoretical values for the isotropic and anisotropic terms and the suitability of these methods was discussed. It is concluded that an intra-molecular eSR is present in all small organic molecular semiconductors. The mechanism behind this eSR was found not to be the HFI but in fact the SO interaction. It is also determined that the eSR is coupling to the vibrations in the molecule and a possible theory based on the curvature of the molecule from the vibrational modes inducing an enhanced SO coupling is proposed, which results in the eSR. The nal part of this thesis looks at the future experiments that have been initiated or can be conducted to further the understanding of spin relaxation and determine the role of a vibrationally enhanced SO coupling.
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Tellez, Galdino Mejia. "Infrared characterization of SiN films on Si for high speed electronics applications." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FTellez.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2004.Thesis advisor(s): Gamani Karunasiri, Ronald E. Brown. Includes bibliographical references (p. 33). Also available online.
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Triplett, Gregory Edward. "Process modeling of InAs/AISb materials for high electron mobility transisitors grown by molecular beam epitaxy." Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06072004-131359/unrestricted/triplett%5Fgregory%5Fe%5F200405%5Fphd.pdf.
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Zheng, Yilong. "Characterization of Charge Transfer Processes Across Perylene Diimide/Electrode Interfaces for Organic Photovoltaic Devices." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/596140.
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Charge transfer efficiency at the organic/transparent conducting oxide (TCO) interface is one of the key parameters controlling the overall efficiency of organic photovoltaics (OPVs). Modification of this interface with a redox-active organic surface modifier may further enhance the charge transfer across the interface by providing a charge-transfer pathway between the electrode and the organic active layer. Functionalized perylene diimide molecules (PDI) are useful for modifying metal oxide/acceptor interfaces for inverted solar cell devices because their LUMO energy level is close to some commonly used acceptor molecules. The effects of PDI structural parameters on the interfacial charge transfer processes across the organic/ITO interface were investigated. Six different PDI monolayers with different structural parameters were deposited on ITO surfaces to investigate the relationship between molecular orientation, linker length, aggregation and charge transfer process. The PDI orientation, degree of PDI aggregation and charge transfer process acrosses PDI/ITO interfaces were characterized by polarized ATR spectroscopy, PM-ATR spectroscopy and photoelectrochemistry. Both linker length and orientation affected the tunneling distance between PDI and ITO, therefore affecting the charge transfer rate constant across the PDI/ITO interfaces. PDI aggregation forced a more out-of-plane orientation of PDI molecules and increased the overall measured charge transfer rate constant. However, PDI aggregation also increased the excited state recombination rate which ultimately led to decrease of the charge collection efficiency. The first application of a PM-TIRF platform to characterize the electron-transfer processes of PDI monomeric films across the organic/electrode interface is presented. The PM-TIRF technique provides higher sensitivity as well as the capability to measure very fast charge transfer events, compared to other commonly used potential-modulated spectroscopy techniques. PDI-phenyl-PA monomeric films exhibited a more in-plane orientation compared with aggregated films and showed a smaller charge transfer rate constant across the PDI/ITO interfaces compared with PDI films with higher degrees of aggregation after normalizing the tunneling distance contributions.
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Ravi, Sankar Ashwin. "Molecular weight effects of PBT-6 polymeric semiconductor on charge carrier mobility." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50414.
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Organic π-conjugated Donor-Acceptor copolymers are emerging as potential candidate materials for organic field effect transistor (OFET) and organic photovoltaic (OPV) applications. The electron-deficient benzothiadiazole group coupled with an electron-rich oligothiophene to form donor-acceptor copolymers has attracted significant attention. These low optical band gap materials absorb photons in the range of 400-800 nm and exhibit good thermal stability. In particular, poly(benzothiadiazole-sexithiophene) (PBT6) exhibits excellent performance in optoelectronic devices and high thermal stability. Here, we present the chemical synthesis and characterization of the polymer, PBT6. Three samples of PBT-6 with differing molecular weights in the range of Mn 18000-45000 Da were synthesized. Each polymer was characterized with respect to its photophysical, thermal properties and field-effected mobility was determined. Devices were prepared by drop-casting polymer solutions in 1,2-dichlorobenzene (DCB) onto an OFET (bottom gate/bottom contact) substrate and the devices were used to examine the charge transport properties of each polymer system. The optimal solvent to be used for processing technique was determined and surface techniques using OTS-8 and OTS-18 were compared through contact angle measurements. The measured charge carrier mobilities were in the range of 0.45-0.6 cm² / V.s. Polymer films prepared via drop-casting and which were thermal annealed exhibit mobilities as high as 0.825 cm² / V.s. This work examines the effect of molecular weight on the charge carrier transport properties and demonstrates the correlation of performance with molecular ordering. Drop-casted films of PBT-6 exhibit highly ordered crystalline lamellar structure with high degree of π- π stacking with edge-on orientation on the substrate. The longer conjugation lengths promote intrachain charge transfer. This high degree of molecular ordering in high MW samples of PBT6 improves the interchain and intrachain charge transfer leading to enhanced mobilities. The increased molecular weight (MW) facilitates in forming more uniform thin films which is vital in processing and application of polymer thin film technologies. These results and observations clearly demonstrate the potential of PBT-6 as a semiconducting material for Optoelectronic devices.
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Fonari, Alexandr. "Theoretical description of charge-transport and charge-generation parameters in single-component and bimolecular charge-transfer organic semiconductors." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54323.
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In this dissertation, we employ a number of computational methods, including Ab Initio, Density Functional Theory, and Molecular Dynamics simulations to investigate key microscopic parameters that govern charge-transport and charge-generation in single-component and bimolecular charge-transfer organic semiconductors.
First, electronic (transfer integrals, bandwidths, effective masses) and electron-phonon couplings of single-component organic semiconductors are discussed. In particular, we evaluate microscopic charge-transport parameters in a series of nonlinear acenes with extended pi-conjugated cores. Our studies suggest that high charge-carrier mobilities are expected in these materials, since large electronic couplings are obtained and the formation of self-localized polarons due to local and nonlocal electron-phonon couplings is unlikely. Next, we evaluate charge detrapping due to interaction with intra-molecular crystal vibrations in order to explain changes in experimentally measured electric conductivity generated by pulse excitations in the IR region of a photoresistor based on pentacene/C60 thin film. Here, we directly relate the nonlocal electron-phonon coupling constants with variations in photoconductivity.
In terms of charge-generation from an excited manifold, we evaluate the modulation of the state couplings between singlet and triplet excited states due to crystal vibrations, in order to understand the effect of lattice vibrations on singlet fission in tetracene crystal. We find that the state coupling between localized singlet and correlated triplet states is much more strongly affected by the dynamical disorder due to lattice vibrations than the coupling between the charge-transfer singlet and triplet states.
Next, the impact of Hartree-Fock exchange in the description of transport properties in crystalline organic semiconductors is discussed. Depending on the nature of the electronic coupling, transfer integrals and bandwidths can show a significant increase as a function of the amount of the Hartree-Fock exchange included in the functional. Similar trend is observed for lattice relaxation energy. It is also shown that the ratio between electronic coupling and lattice relaxation energy is practically independent of the amount of the Hartree-Fock exchange, making this quantity a good candidate for incorporation into tight-binding transport models. We also demonstrate that it is possible to find an amount of the Hartree-Fock exchange that recovers (quasi-particle) band structure obtained from a highly accurate G0W0 approach. Finally, a microscopic understanding of a phase transition in charge-carrier mobility from temperature independent to thermally activated in stilbene-tetrafluoro-tetracyanoquinodimethane crystal is provided.
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Sánchez-Carrera, Roel S. "Theoretical characterization of charge transport in organic molecular crystals." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26579.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Brédas, Jean-Luc; Committee Member: Kippelen, Bernard; Committee Member: Marder, Seth; Committee Member: Sherrill, David; Committee Member: Whetten, Robert. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Fu, Boyi. "Design and syntheses of hole and electron transport donor-acceptor polymeric semiconductors and their applications to organic field-effect transistors." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54868.
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The π-conjugated organic and polymeric semiconducting materials have attracted much attention in the past years due to their significant potential in applications to electronic and optoelectronic devices including organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic light-emitting diodes (OLEDs), etc. Yet, organic and polymeric semiconductors still have challenges associated with their relatively low charge carrier (hole and electron) transport mobilities and ambient stability in OFET applications.
This dissertation discusses the molecular engineering on backbones and side-chains of π-conjugated semiconducting polymers to enhance the hole and electron field-effect mobilities. Three donor-acceptor copolymers, the hole transport (p-type) poly(hexathiophene-co-benzo- thiazole) (PBT6), the hole transport poly(thiophenes-benzothiadiazole-thiophenes-diketopyrrolo- pyrrole) (pTBTD), and the electron transport (n-type) poly(dithieno-diketopyrrolopyrrole-bithiazole) (PDBTz) have been developed. Besides, the effect of polymer side chains on polymer solution-processability and charge carrier transport properties was systematically investigated: a side chain 5-decylheptadecyl having the branching position remote from the polymer backbone merges the advantages of the improved solubility from traditional branched side chains in which the branch chains are close to polymer backbone and the effective π-π intermolecular interactions commonly associated with linear side chains. This indicates the potential of side chain engineering to facilitate the charge carrier transport performance of organic and polymeric semiconductors. Additionally, PDBTz solution-processing to OFETs based on non-halogenated solvents (xylenes and tetralin) was studied. The resultant thin-film OFET devices based on non-halogenated solvents exhibited similar film morphology and field-effect electron mobilities as the counterparts based on halogenated solvents, indicative of the feasibility of developing high mobility OFET devices through more environmentally-benign processing.
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Chan, Yiu Him. "Effect of dopants and gate dielectrics on charge transport and performance of organic thin film transistor." HKBU Institutional Repository, 2012. https://repository.hkbu.edu.hk/etd_ra/1450.
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Fix, Aaron. "Synthesis and Properties of Indenofluorene and Diindenothiophene Derivatives for Use as Semiconducting Materials in Organic Electronic Devices." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13444.
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Organic electronic devices are becoming commonplace in many academic and industrial materials laboratories, and commercial application of these technologies is underway. To maximize our fundamental understanding of organic electronics, a wide array of molecular frameworks is necessary, as it allows for a variety of optical and electronic properties to be systematically investigated. With the ability to further tune each individual scaffold via derivatization, access to a broad spectrum of interesting materials is possible. Of particular interest in the search for organic semiconducting materials are the cyclopenta-fused polyaromatic hydrocarbons, including those based on the fully conjugated indenofluorene (IF) system, which is comprised of five structural isomers. This dissertation represents my recent contributions to this area of research.
Chapter I serves as a historical perspective on early indenofluorene research and a review of more current research on their synthesis and applications in organic electronic devices. Chapters II and III cover our early work developing the synthesis of the fully-reduced indeno[1,2-b]fluorene scaffold, with the latter of these chapters showing the first example of its application in an organic electronic device, a field effect transistor. Chapter IV demonstrates the first syntheses of fully-reduced indeno[2,1-c]fluorene derivatives. Chapter V expands our research to encompass isoelectronic heteroatomic derivatives of that same scaffold, introducing the fully-reduced diindeno[2,1-b:1',2'-d]thiophene scaffold and showing that our synthetic methodology also can be used to produce a quinoidal thiophene core. Chapter VI concludes with a review of the similarities between the indeno[2,1-c]fluorene and diindeno[2,1-b:1',2'-d]thiophene molecular architectures and introduces benzo[a]indeno[2,1-b]fluorene derivatives, demonstrating the first example of a fully-reduced indenofluorene that possesses a non-quinoidal core, illustrating that the quinoidal core is not a prerequisite for the strong electron affinities seen across the families of fully-reduced indenofluorenes.
This dissertation encompasses previously published and unpublished co-authored material.2015-10-10
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Senevirathna, Wasana. "Azadipyrromethene-based Metal Complexes as 3D Conjugated Electron Acceptors for Organic Solar Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1402062085.
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Auth, Michael Tilman [Verfasser], Vladimir [Gutachter] Dyakonov, and Tobias [Gutachter] Hertel. "Quantitative Electron Paramagnetic Resonance Studies of Charge Transfer in Organic Semiconductors / Michael Tilman Auth ; Gutachter: Vladimir Dyakonov, Tobias Hertel." Würzburg : Universität Würzburg, 2020. http://d-nb.info/1219429880/34.
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Pokhrel, Chandra Prasad. "Crystal growth and charge carrier transport in liquid crystals and other novel organic semiconductors." [Kent, Ohio] : Kent State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1254234736.
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Thesis (Ph.D.)--Kent State University, 2009.Title from PDF t.p. (viewed April 1, 2010). Advisor: Brett Ellman. Keywords: Laser; Charge generation; Charge transport; Mobility; Trapping; Space charge; Hopping; Tunneling; Lattice vibration; Exciton; Polaron; HUMO; LUMO; Action Spectrum; Quantum efficiency; Crystal Growth; Liquid crystal; Disordered medium. Includes bibliographical references.
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Moudgil, Karttikay. "Design and development of dimeric sandwich compounds as n-dopants for organic electronics." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54958.
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Electrical doping of organic semiconductors with molecular oxidants (p-type) or reductants (n-type) can greatly improve charge injection and conductivity in devices. Simple one electron reductants that are capable of reducing most electron-transport materials will inevitably also be sensitive to reaction with oxygen. Coupling electron transfer step with bond breaking/ making processes in principle can address this problem. The rhodocene dimer and related ruthenium and iridium dimeric sandwich compounds have been discussed as example of such n-dopants, reducing a variety of organic semiconductors to the corresponding radical anions, while forming monomeric cations. This class of n-dopants can be used in both vapor- and solution-processed devices, and the dopant monomer cations are large and, therefore, fairly stable with respect to diffusion. This thesis focused on increasing the utility of these and related electrical dopants. In order to reduce various electron-transport materials with lower electron affinities, which are frequently used in OLEDs, strategies and limitations to develop stronger n-dopants is discussed. Controlling the kinetics of the dopant / semiconductor reactions to allow film processing in ambient conditions, with activation of the dopants being carried out thermally or photochemically in subsequent steps is presented. An approach to covalently tether monomeric cations with themselves, surfaces or electron-transport materials is described. Electrochemical studies that further our understanding of dopant kinetics and thermodynamics is described. The dimer dopant chemistry is also compared to the corresponding hydride-reduced complexes of the cations and manganese tricarbonyl benzene dimer. The directions for future dopant design with improved properties is discussed.
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Ivancová, Anna. "Elektrické transportní vlastnosti molekulárních materiálů pro pokročilé aplikace." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2012. http://www.nusl.cz/ntk/nusl-216894.
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This master´s thesis deals with possibilities of application of new organic molecular materials for electronic devices. Nowadays it is a very attractive field of research, because of the tendencies in industry to miniaturize, reduce production costs and develop new, eco-friendlier, processes of production. The theoretical part of the thesis provides a short overview of organic materials suitable for smart applications and thin films issues including their characterization. The experimental part is dedicated to means how to prepare thin-film electronic components to silicon wafers for thin films field effect transistors. The obtained results in the last part of thesis are discussed about properties of prepared thin films, in the concrete about the electrical transport properties, in the connection with the condition of preparation.
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Sánchez-Carrera, Roel S. "Theoretical characterization of charge transport in organic molecular crystals." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26579.
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In this thesis, a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals has been developed. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. The nature of the intramolecular vibronic coupling in oligoacenes and oligothienoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. The electron interactions with optical phonons in oligoacene single crystals were investigated using both density functional theory and empirical force field methods. The low-frequency optical modes are found to play a significant role in dictating the temperature dependence of the charge-transport properties in the oligoacene crystals. The microscopic charge-transport parameters in the pentathienoacene, 1,4-diiodobenzene, and 2,6-diiodo-dithieno[3,2-b:2',3'-d]thiophene crystals were also investigated. It was found that the intrinsic charge transport properties in the pentathienoacene crystal might be higher than that in two benchmark high-mobility organic crystals, i.e., pentacene and sexithienyl. For 1,4-diiodobenzene crystal, a detailed quantum-mechanical study indicated that its high mobility is primarily associated with the iodine atoms. In the 2,6-diiododithieno[3,2-b:2',3'-d]thiophene crystal, the main source of electronic interactions were found along the π-stacking direction. For negatively charged carriers, the halogen-functionalized molecular crystals show a very large polaron binding energy, which suggests significantly low charge-transport mobility for electrons.
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Appleton, Anthony Lucas. "Synthesis and characterization of large linear heteroacenes and their derivatives." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37225.
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The work presented in this thesis is primarily concerned with the synthesis and characterization of large, linear heteroacenes and their derivatives. We have been able to significantly expand on the types of materials available for application in organic electronic device architectures. In particular, the work focused on solution processible and novel derivatives of thiadiazoles, diazatetracenes, diazapentacenes, tetrazapentacences, and N,N-dihydrotetraazaheptacene. Extensive computational studies have been performed in order to better understand the optoelectronic properties of these materials. Although no devices have been fabricated that show appreciable hole or electron mobility, the properties of these materials are very promising. Besides our work on organic electronic materials for application in optoelectronic devices, we have also been able to develop, via the Click reaction, a series of aqueous metal sensors for copper (II), nickel (II), and silver (I) based upon fluorescence quenching. The use of a modified Stern-Volmer equation was necessary to fit the data in order to obtain binding constants. The exploration of new materials and their properties in the area of organic electronics is an exciting field for the synthetic organic chemist, as the goals associated with this work strive to impact humanity in a positive manner by reducing energy costs.
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Weiler, Christoph Karl Felix [Verfasser], and Hans Georg [Akademischer Betreuer] Bock. "Optimum Experimental Design for the Identification of Gaussian Disorder Mobility Parameters in Charge Transport Models of Organic Semiconductors / Christoph Karl Felix Weiler ; Betreuer: Hans Georg Bock." Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1179925246/34.
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Billingsley, Daniel D. "Feasibility study of III-nitride-based transistors grown by ammonia-based metal-organic molecular beam epitaxy." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34859.
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III-nitrides are a promising material system with unique material properties, which allows them to be utilized in a variety of semiconductor devices. III-nitrides grown by NH3-MOMBE are typically grown with high carbon levels (> 1021 cm-3) as a result of the incomplete surface pyrolysis of the metal-organic sources. Recent research has involved the compensating nature of carbon in III-nitrides to produce semi-insulating films, which can provide low-leakage buffer layers in transistor devices. The aim of this work is to investigate the possibility of forming a 2DEG, which utilizes the highly carbon-doped GaN layers grown by NH3-MOMBE to produce low-leakage buffer layers in the fabrication of HEMTs. These low leakage GaN buffers would provide increased HEMT performance, with better pinch-off, higher breakdown voltages and increased power densities. Additionally, methods of controlling and/or reducing the incorporation of carbon will be undertaken in an attempt to broaden the range of possible device applications for NH3-MOMBE. To realize these transistor devices, optimization and improved understanding of the growth conditions for both GaN and AlGaN will be explored with the ultimate goal of determining the feasibility of III-nitride transistors grown by NH3-MOMBE.
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Fischer, Janine. "Density of States and Charge Carrier Transport in Organic Donor-Acceptor Blend Layers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-184493.
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In the last 25 years, organic or "plastic" solar cells have gained commercial interest as a light-weight, flexible, colorful, and potentially low-cost technology for direct solar energy conversion into electrical power. Currently, organic solar cells with a maximum power conversion effciency (PCE) of 12% can compete with classical silicon technology under certain conditions. In particular, a variety of strongly absorbing organic molecules is available, enabling custom-built organic solar cells for versatile applications. In order to improve the PCE, the charge carrier mobility in organic thin films must be improved. The transport characterization of the relevant materials is usually done in neat layers for simplicity. However, the active layer of highly efficient organic solar cells comprises a bulk heterojunction (BHJ) of a donor and an acceptor component necessary for effective charge carrier generation from photo-generated excitons. In the literature, the transport properties of such blend layers are hardly studied. In this work, the transport properties of typical BHJ layers are investigated using space-charge limited currents (SCLC), conductivity, impedance spectroscopy (IS), and thermally stimulated currents (TSC) in order to model the transport with numerical drift-diffusion simulations. Firstly, the influence of an exponential density of trap states on the thickness dependence of SCLCs in devices with Ohmic injection contacts is investigated by simulations. Then, the results are applied to SCLC and conductivity measurements of electron- and hole-only devices of ZnPc:C60 at different mixing ratios. Particularly, the field and charge carrier density dependence of the mobility is evaluated, suggesting that the hole transport is dominated by exponential tail states acting as trapping sites. For comparison, transport in DCV5T-Me33:C60, which shows better PCEs in solar cells, is shown not to be dominated by traps. Furthermore, a temperature-dependent IS analysis of weakly p-doped ZnPc:C60 (1:1) blend reveals the energy-resolved distribution of occupied states, containing a Gaussian trap state as well as exponential tail states. The obtained results can be considered a basis for the characterization of trap states in organic solar cells. Moreover, the precise knowledge of the transport-relevant trap states is shown to facilitate modeling of complete devices, constituting a basis for predictive simulations of optimized device structuresOrganische oder "Plastik"-Solarzellen haben in den letzten 25 Jahren eine rasante Entwicklung durchlaufen. Kommerziell sind sie vor allem wegen ihres geringen Gewichts, Biegsamkeit, Farbigkeit und potentiell geringen Herstellungskosten interessant, was zukünftig auf spezielle Anwendungen zugeschnittene Solarzellen ermöglichen wird. Die Leistungseffzienz von 12% ist dabei unter günstigen Bedingungen bereits mit klassischer Siliziumtechnologie konkurrenzfähig. Um die Effzienz weiter zu steigern und damit die Wirtschaftlichkeit zu erhöhen, muss vor allem die Ladungsträgerbeweglichkeit verbessert werden. In organischen Solarzellen werden typischerweise Donator-Akzeptor-Mischschichten verwendet, die für die effziente Generation freier Ladungsträger aus photo-induzierten Exzitonen verantwortlich sind. Obwohl solche Mischschichten typisch für organische Solarzellen sind, werden Transportuntersuchungen der relevanten Materialien der Einfachheit halber meist in ungemischten Schichten durchgeführt. In der vorliegenden Arbeit wird der Ladungstransport in Donator-Akzeptor-Mischschichten mithilfe raumladungsbegrenzter Ströme (space-charge limited currents, SCLCs), Leitfähigkeit, Impedanzspektroskopie (IS) und thermisch-generierter Ströme (thermally stimulated currents, TSC) untersucht und mit numerischen Drift-Diffusions-Simulationen modelliert. Zunächst wird mittels Simulation der Einfluss exponentiell verteilter Fallenzustände auf das schichtdickenabhängige SCLC-Verhalten unipolarer Bauelemente mit Ohmschen Kontakten untersucht. Die Erkenntnisse werden dann auf Elektronen- und Lochtransport in ZnPc:C60-Mischschichten mit verschiedenen Mischverhältnissen angewendet. Dabei wird die Beweglichkeit als Funktion von elektrischem Feld und Ladungsträgerdichte dargestellt, um SCLC- und Leitfähigkeitsmessungen zu erklären, was mit einer exponentiellen Fallenverteilung gelingt. Zum Vergleich werden dieselben Untersuchungen in DCV2-5T-Me33:C60, dem effizientesten der bekannten Solarzellenmaterialien dieser Art, wiederholt, ohne Anzeichen für fallendominierten Transport. Des weiteren werden erstmals schwach p-dotierte ZnPc:C60-Mischschichten mit temperaturabhängiger IS untersucht, um direkt die Dichte besetzter Lochfallenzustände zu bestimmen. Dabei werden wiederum exponentielle Fallenzustände sowie eine Gaußförmige Falle beobachtet. Insgesamt tragen die über Fallenzustände in Mischschichten gewonnenen Erkenntnisse zum Verständnis von Transportprozessen bei und bilden damit eine Grundlage für die systematische Identifizierung von Fallenzuständen in Solarzellen. Außerdem wird gezeigt, dass die genaue Beschreibung der transportrelevanten Fallenzustände die Modellierung von Bauelementen ermöglicht, auf deren Grundlage zukünftig optimierte Probenstrukturen vorhergesagt werden können
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Stříteský, Stanislav. "Organické materiály pro organické polem řízené tranzistory a elektrochemické transistory." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2020. http://www.nusl.cz/ntk/nusl-432987.
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Tato práce je zaměřena na studium vlastností organických polovodivých materiálů se zaměřením na jejich vodivost a pohyblivost nosičů náboje. Hlavním cílem této práce je objasnit vztah mezi chemickou strukturou organických polovodičů a jejich vlastnostmi. Teoretická část práce je zaměřena na základy organických polovodičů, transport náboje a přehled vlastností organických polovodivých materiálů, které vedly k jejich aplikaci v polních a elektrochemických tranzistorech. Experimentální část představuje přehled použitých materiálů, způsoby jejich přípravy a charakterizační metody. V rámci výsledkové části bylo vyvinuto nebo optimalizováno několik metod pro přípravu tenkých vrstev a následně byl studován jejich vliv na výkon organických polem řízených tranzistorů. Byly charakterizovány a diskutovány relevantní vlastnosti nových organických polovodivých materiálů se zaměřením na pohyblivost nosičů náboje. Byla charakterizována a diskutována biokompatibilita několika organických polovodičů. Elektrické vlastnosti, stabilita a biokompatibilita elektroaktivních polymerních inkoustů na bázi PEDOT:PSS byla charakterizována a diskutována s ohledem na jejich možné použití v bioelektronice. Nakonec byl zkonstruován organický bioelektronický senzor pro detekci fyziologické odpovědi kardiomyocytů na základě studovaných materiálů.
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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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Gamarra, Piero. "Étude de composés semiconducteurs III-N à forte teneur en indium : application à l'optimisation des hétérostructures pour transistors à effet de champ piézo-électriques (HEMT)." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10009.
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Cette thèse est une contribution à l'étude de composés semiconducteurs InX Al1-X N à forte teneur en Indium. Ces composés présentent des propriétés très intéressantes pour des applications dans le domaine de l'amplification des hyperfréquences. L'objectif principal de la thèse est de définir des hétéro-structures de type AlGaInN / GaN, pour transistors à Effet de Champ Piézoélectrique (HEMT), épitaxiées sur substrats de saphir, silicium, et SiC, optimisées en vue de l'amplification hyperfréquence. Dans la première partie, nous étudions la croissance épitaxiale de couches minces du composé binaire GaN, en phase vapeur, à partir de précurseurs organométalliques (MOVPE), dans des conditions optimisées pour obtenir des couches fortement résistives. La deuxième partie est consacrée à l'étude de structures HEMT AlGaN/GaN sur SiC et sur silicium. Sur SiC, nous montrons la forte influence des propriétés du substrat sur les propriétés électriques des structures HEMT. Nous avons étudié une structure nouvelle incluant une fine couche de AlN entre les couches AlGaN et GaN et évalué les performances de transistors HEMT AlGaN/GaN et AlGaN/AlN/GaN sur SiC et sur Silicium (111). La partie suivante est consacrée à la croissance de composés ternaires InAlN. Nous avons étudié l'influence de la température de croissance et du rapport V/III sur les propriétés structurales de InAlN. Les conditions optimales ont été utilisées pour la réalisation de structures HEMT InAlN/AlN/GaN. Nous démontrons l'influence considérable de la couche AlN sur les propriétés électriques de ces structures. Enfin, nous discutons les performances obtenues sur des transistors à effet de champ InAlN/AlN/GaN sur SiCThis work reports on the metal-organic vapor phase epitaxy and on the characterisation of III-N GaInAlN heterostructures for High Electron Mobility Transistors. In a first part, the heteroepitaxy of semiinsulating GaN layers on sapphire, SiC and silicon is presented as the basis for the subsequent growth of III-N HEMT structures. The influence of suitable nucleation layers on the properties of GaN is presented and discussed. A second part deals with AlGaN/GaN HEMT structures grown on SiC and on Si (111) wafers. The influence of SiC substrate properties on the electrical performances of AlGaN/GaN HEMT is presented. A novel structure, including a thin AlN interlayer between the GaN buffer layer and the AlGaN barrier layer has also been introduced. The section is completed by device results obtained on selected heterostructures. A study of the impact of selected growth parameter (i.e. growth temperature, V/III ratio) on the structural and surface properties of InAlN layers is then presented. The optimized conditions have been used for the growth InAlN/AlN/GaN HEMT structures which have been thoroughly characterized. The electrical properties of the structures were found to be strongly dependent on the growth conditions of the AlN interlayer (e.g. deposition time, V/III ratio). Finally, state of the art device results obtained with InAlN/AlN/GaN heterostructures are presented
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Schober, Christoph Otto [Verfasser], Karsten [Akademischer Betreuer] [Gutachter] Reuter, Peter [Gutachter] Müller-Buschbaum, Jochen [Gutachter] Blumberger, and Ulrich K. [Gutachter] Heiz. "Ab Initio Charge Carrier Mobility and Computational Screening of Molecular Crystals for Organic Semiconductors / Christoph Otto Schober ; Gutachter: Peter Müller-Buschbaum, Karsten Reuter, Jochen Blumberger, Ulrich K. Heiz ; Betreuer: Karsten Reuter." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1124590994/34.
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Ebenhoch, Bernd. "Organic solar cells : novel materials, charge transport and plasmonic studies." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7814.
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Organic solar cells have great potential for cost-effective and large area electricity production, but their applicability is limited by the relatively low efficiency. In this dissertation I report investigations of novel materials and the underlying principles of organic solar cells, carried out at the University of St Andrews between 2011 and 2015. Key results of this investigation: • The charge carrier mobility of organic semiconductors in the active layer of polymer solar cells has a rather small influence on the power conversion efficiency. Cooling solar cells of the polymer:fullerene blend PTB7:PC₇₁BM from room temperature to 77 K decreased the hole mobility by a factor of thousand but the device efficiency only halved. • Subphthalocyanine molecules, which are commonly used as electron donor materials in vacuum-deposited active layers of organic solar cells, can, by a slight structural modification, also be used as efficient electron acceptor materials in solution-deposited active layers. Additionally these acceptors offer, compared to standard fullerene acceptors,advantages of a stronger light absorption at the peak of the solar spectrum. • A low band-gap polymer donor material requires a careful selection of the acceptor material in order to achieve efficient charge separation and a maximum open circuit voltage. • Metal structures in nanometer-size can efficiently enhance the electric field and light absorption in organic semiconductors by plasmonic resonance. The fluorescence of a P3HT polymer film above silver nanowires, separated by PEDOT:PSS, increased by factor of two. This could be clearly assigned to an enhanced absorption as the radiative transition of P3HT was identical beside the nanowires. • The use of a processing additive in the casting solution for the active layer of organic solar cells of PTB7:PC₇₁BM strongly influences the morphology, which leads not only to an optimum of charge separation but also to optimal charge collection.
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Forker, Roman. "Electronic Coupling Effects and Charge Transfer between Organic Molecules and Metal Surfaces." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-26163.
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We employ a variant of optical absorption spectroscopy, namely in situ differential reflectance spectroscopy (DRS), for an analysis of the structure-properties relations of thin epitaxial organic films. Clear correlations between the spectra and the differently intense coupling to the respective substrates are found. While rather broad and almost structureless spectra are obtained for a quaterrylene (QT) monolayer on Au(111), the spectral shape resembles that of isolated molecules when QT is grown on graphite. We even achieve an efficient electronic decoupling from the subjacent Au(111) by inserting an atomically thin organic spacer layer consisting of hexa-peri-hexabenzocoronene (HBC) with a noticeably dissimilar electronic behavior. These observations are further consolidated by a systematic variation of the metal substrate (Au, Ag, and Al), ranging from inert to rather reactive. For this purpose, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is chosen to ensure comparability of the molecular film structures on the different metals, and also because its electronic alignment on various metal surfaces has previously been studied with great intensity. We present evidence for ionized PTCDA at several interfaces and propose the charge transfer to be related to the electronic level alignment governed by interface dipole formation on the respective metalsZur Analyse der Struktur-Eigenschafts-Beziehungen dünner, epitaktischer Molekülfilme wird in situ differentielle Reflexionsspektroskopie (DRS) als Variante der optischen Absorptionsspektroskopie verwendet. Klare Zusammenhänge zwischen den Spektren und der unterschiedlich starken Kopplung zum jeweiligen Substrat werden gefunden. Während man breite und beinahe unstrukturierte Spektren für eine Quaterrylen (QT) Monolage auf Au(111) erhält, ist die spektrale Form von auf Graphit abgeschiedenem QT ähnlich der isolierter Moleküle. Durch Einfügen einer atomar dünnen organischen Zwischenschicht bestehend aus Hexa-peri-hexabenzocoronen (HBC) mit einem deutlich unterschiedlichen elektronischen Verhalten gelingt sogar eine effiziente elektronische Entkopplung vom darunter liegenden Au(111). Diese Ergebnisse werden durch systematische Variation der Metallsubstrate (Au, Ag und Al), welche von inert bis sehr reaktiv reichen, untermauert. Zu diesem Zweck wird 3,4,9,10-Perylentetracarbonsäuredianhydrid (PTCDA) gewählt, um Vergleichbarkeit der molekularen Filmstrukturen zu gewährleisten, und weil dessen elektronische Anordnung auf verschiedenen Metalloberflächen bereits eingehend untersucht worden ist. Wir weisen ionisiertes PTCDA an einigen dieser Grenzflächen nach und schlagen vor, dass der Ladungsübergang mit der elektronischen Niveauanpassung zusammenhängt, welche mit der Ausbildung von Grenzflächendipolen auf den entsprechenden Metallen einhergeht
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Fernando, Juwanmandadige Roshan. "Tuning the Opto-Electronic Properties of Core-Substituted Naphthalenediimides through Imide Substitution." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1401984667.
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Apicella, Fernandez Sergio. "Surface energy modification of metal oxide to enhance electron injection in light-emitting devices : charge balance in hybrid OLEDs and OLETs." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-25097.
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Organic semiconductors (OSCs) present an electron mobility lower by several orders of magnitude than the hole mobility, giving rise to an electron-hole charge imbalance in organic devices such as organic light-emitting diodes (OLEDs) and organic light-emitting transistors (OLETs). In this thesis project, I tried to achieve an efficient electron transport and injection properties in opto-electronic devices, using inorganic n-type metal oxides (MOs) instead of organic n-type materials and a polyethyleneimine ethoxylated (PEIE) thin layer as electron transport (ETLs) and injection layers (EILs), respectively. In the first part of this thesis, inverted OLEDs were fabricated in order to study the effect of the PEIE layer in-between ZnO and two different emissive layers (EMLs): poly(9,9-dioctylfluorene-alt-benzothiadiazole) polymer (F8BT) and tris(8-hydroxyquinolinato) aluminum small molecule (Alq3), based on a solution and thermal evaporation processes, respectively. Different concentrations (0.80 %, 0.40 %) of PEIE layers were used to further study electron injection capability in OLEDs. After a series of optimizations in the fabrication process, the opto-electrical characterization showed high-performance of devices. The inverted OLEDs reported a maximum luminance over 104 cd m-2 and a maximum external quantum efficiency (EQE) around 1.11 %. The results were attributed to the additional PEIE layer which provided a good electron injection from MOs into EMLs. In the last part of the thesis, OLETs were fabricated and discussed by directly transferring the energy modification layer from OLEDs to OLETs. As metal oxide layer, ZnO:N was employed for OLETs since ZnO:N-based thin film transistors (TFTs) showed better performance than ZnO-based TFTs. Finally, due to their short life-time, OLETs were characterized electrically but not optically.
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Attah, Isaac Kwame. "BINDING ENERGIES AND SOLVATION OF ORGANIC MOLECULAR IONS, REACTIONS OF TRANSITION METAL IONS WITH, AND PLASMA DISCHARGE IONIZATION OF MOLECULAR CLUSTERS." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/525.
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In this dissertation, different approaches have been employed to address the quest of understanding the formation and growth mechanisms of carbon-containing molecular ions with relevance to astrochemistry. Ion mobility mass spectrometry and DFT computations were used to investigate how a second nitrogen in the pyrimidine ring will affect the formation of a covalent bond between the benzene radical cation and the neutral pyrimidine molecule, after it was shown that a stable covalent adduct can be formed between benzene radical cation and the neutral pyridine. Evidence for the formation of a more stable covalent adduct between the benzene radical cation and the pyrimidine is reported here. The effect of substituents on substituted-benzene cations on their solvation by an HCN solvent was also investigated using ion mobility mass spectrometry and DFT computations were also investigated. We looked at the effect of the presence of electron-withdrawing substituents in fluorobenzene, 1,4 di- fluorobenzene, and benzonitrile on their solvation by up to four HCN ligands, and compared it to previous work done to determine the solvation chemistry of benzene and phenylacetylene by HCN. We report here the observed increase in the binding of the HCN molecule to the aromatic ring as the electronegativity of the substituent increased. We also show in this dissertation, DFT calculations that reveal the formation of both hydrogen-bonded and electrostatic isomers, of similar energies for each addition to the ions respectively. The catalytic activity of the 1st and 2nd row TM ions towards the polymerization of acetylene done using the reflectron time of flight mass spectrometry and DFT calculations is also reported in this dissertation. We explain the variation in the observed trend in C-H/C-C activity of these ions. We also report the formation of carbide complexes by Zr+, Nb+, and Mo+, with the acetylene ligands, and show the thermodynamic considerations that influence the formation of these dehydrogenated ion-ligand complexes. Finally, we show in this dissertation, a novel ionization technique that we employed to generate ions that could be relevant to the interstellar and circumstellar media using the reflectron time of flight mass spectrometry.
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Venkatachalam, Anusha. "Investigation of self-heating and macroscopic built-in polarization effects on the performance of III-V nitride devices." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29669.
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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.Committee Chair: Yoder, Douglas; Committee Member: Graham, Samuel; Committee Member: Allen, Janet; Committee Member: Klein, Benjamin; Committee Member: Voss, Paul. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Szymanski, Robin. "Vers l’industrialisation des cellules solaires organiques ternaires." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0298.
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L’énergie solaire photovoltaïque organique (OPV) est une technologie émergente exempte de matériaux rares et à faibles coûts énergétiques de production. Ces modules, composés de plusieurs couches minces empilées, peuvent être souples, semi-transparents et de différentes formes et couleurs, permettant de les intégrer dans le paysage urbain ou aux objets du quotidien. A l’échelle laboratoire, les rendements de conversion énergétique reportés en OPV n’ont cessé de croitre d’année en année, grâce en particulier à l’émergence de nouvelles couches actives, classiquement composées de deux semi-conducteurs organiques, l’un donneur d’électrons, l’autre accepteur d’électrons (système binaire). Il a été montré qu’il est possible d’en ajouter un troisième pour former un mélange ternaire afin d’améliorer les performances tout en gardant les mêmes coûts de production. Le but de cette thèse est donc de comprendre l’impact du troisième composé et de développer des solutions innovantes tout en intégrant les contraintes liées à leur industrialisation. Dans un premier temps, des couches binaires à base des polymères DT-PDPP2T-TT et PTQ10 ont été mises au point en respectant ces contraintes. Leurs performances prometteuses ont servi de socle à l’étude des mélanges ternaires. Le premier raisonnement s’est basé sur l’augmentation de la densité de courant de court-circuit en ajoutant un composé présentant un spectre d’absorption solaire complémentaire. Cette démarche n’a pas été concluante car le facteur de forme diminuait fortement. Il a alors été décidé de se concentrer sur ce paramètre en ajoutant du PC61BM, accepteur à forte mobilité d’électrons. Cette stratégie a permis de porter les rendements de conversion jusqu’à 10.3% en conditions semi-industrielles avec un solvant non toxique et jusqu’à 14.7% avec un solvant halogéné. Cette amélioration a été attribuée à des changements morphologiques impactant le transport de charge. De plus, lorsque les accepteurs sont miscibles, la tension en circuit ouvert est proportionnelle au ratio entre les deux accepteurs. Une approche prédictive basée sur les énergies de surface a ensuite été menée pour mesurer la compatibilité des matériaux entre eux. Les dispositifs ternaires à base de PTQ10 : 4TIC-4F : PC61BM ont montré une meilleure photostabilité. Pour finir, une étude de pré-industrialisation s’est avérée concluante en vue d’essais à plus grande échelleOrganic photovoltaics (OPV) is a promising solar energy technology excluding the usage of rare elements and with low production costs. These multilayer OPV modules can be flexible, semi-transparent and with various colors enabling innovative usage in the urban landscape and on our everyday technological items. At lab scale, over the years, the power conversion efficiency of OPV cells grew up dramatically, especially thanks to the development of novel active layers, blends of two organic semiconductors, one electron donor and one electron acceptor (binary system). Recently, it has been shown that adding a third material in the active layer, forming a ternary blend, increases the performances. This strategy is of interest for the OPV industry by maintaining the low production costs of the modules. Therefore, this work aims to understand the role of this third component and to develop innovative active layers while respecting the industrial requirements for large-scale production. First, we focused on binary blends with PTQ10 and DT-PPDT2T-TT as polymeric donors. Promising efficiencies were achieved on these binary systems as a base for our ternary studies. We tried to increase the short circuit current by adding a third organic semiconductor with complementary light absorption. This approach was not successful because the fill factor dropped drastically. Thus, we focused on improving this parameter by adding the well-known fullerene acceptor PC61BM. This strategy enabled to increase the efficiency up to 10.3% in semi-industrial conditions with a non-toxic solvent and up to 14.7% in halogenated solvent. Morphological changes were responsible of charge transport improvement, which has proven to be one of the key factor in ternary blends. In addition, the open circuit voltage has been shown proportional to the weight ratio between both acceptors when they form an alloy. Based on these studies, we developed a predictive approach to assess the compatibility between the materials. Finally, ternary PTQ10:4TIC-4F:PC61BM devices turned out to be the most promising in terms of pre-industrialization and photostability
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Wagner, Christian. "Potential Energy Minimization as the Driving Force for Order and Disorder in Organic Layers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-38242.
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The topic of this work is the structural characterization and theoretical modeling of organic single and heterolayers. The growth of sub-monolayers and monolayers (ML) of the two polycyclic aromatic hydrocarbons quaterrylene (QT) and hexa-peri-hexabenzocoronene (HBC) on Ag(111) and Au(111) was investigated. A transition from a disordered, isotropic phase to an ordered phase with increasing coverage was found. The lattice of the ordered phase turned out to be coverage dependent. The intermolecular potential was modeled including Coulomb and van der Waals interaction by a force-field approach. The postulated repulsive character of the potential could be connected to the non-uniform intramolecular charge distribution and to a screening of the van der Waals forces. Furthermore, the influence of the variable lattice constant on the epitaxial growth of HBC was studied. The second part of this work deals with a ML of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on a ML of HBC. In dependency on the initial lattice constant of HBC, a total of three line-on-line (LOL) and point-on-line coincident phases of PTCDA (with respect to HBC) was found. Following an analysis of the general properties of LOL coincident systems via force-field calculations, a new method to predict the structure of such systems is introducedThema dieser Arbeit ist die strukturelle Charakterisierung von organischen Einfach- und Heterolagen sowie deren theoretische Beschreibung und Modellierung. Es wurden Submonolagen und Monolagen (ML) der polyzyklischen Kohlenwasserstoffe Quaterrylen (QT) und Hexa-peri-hexabenzocoronen (HBC) auf Ag(111) und Au(111) Einkristallen untersucht und ein Übergang von einer ungeordneten, isotropen Phase zu einer geordneten Phase mit steigender Bedeckung beobachtet. Die geordnete Phase wies dabei bedeckungsabhängige Gitterkonstanten auf. Das intermolekulare Potential wurde unter Berücksichtigung von Coulomb und van der Waals Anteilen mittels Kraftfeldmethoden modelliert. Der postulierte repulsive Charakter des Potentials konnte auf die Ladungsverteilung im Molekül und eine Abschwächung des van der Waals Potentials zurückgeführt werden. Weiterhin wurde der Einfluss der variablen HBC Gitterkonstante auf die epitaktische Relation des Gitters zum Metallsubstrat untersucht. Der zweite Teil der Arbeit widmet sich der Untersuchung einer ML 3,4,9,10-Perylenetetracarboxylic dianhydrid (PTCDA) auf einer ML HBC. Dabei wurden, in Abhängigkeit von der HBC Gitterkonstante, insgesamt drei verschiedene Typen von line-on-line bzw. point-on-line Epitaxie nachgewiesen. Im Anschluss an eine Analyse der generellen Eigenschaften solcher epitaktischer Lagen mittels Kraftfeldrechnungen wird eine neue Methode zur Vorhersage der Struktur konkreter Systeme vorgestellt
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Umana-Membreno, Gilberto A. "A study of gamma-radiation-induced effects in gallium nitride based devices." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2006. http://theses.library.uwa.edu.au/adt-WU2007.0015.
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[Truncated abstract] Over the past decade, the group III-nitride semiconducting compounds (GaN, AlN, InN, and their alloys) have attracted tremendous research efforts due to their unique electronic and optical properties. Their low thermal carrier generation rates and large breakdown fields make them attractive for the development of robust electronic devices capable of reliable operation in extreme conditions, i.e. at high power/voltage levels, high temperatures and in radiation environments. For device applications in radiation environments, such as space electronics, GaN-based devices are expected to manifest superior radiation hardness and reliability without the need for cumber- some and expensive cooling systems and/or radiation shielding. The principle aim of this Thesis is to ascertain the level of susceptibility of current GaN-based elec- tron devices to radiation-induced degradation, by undertaking a detailed study of 60Co gamma-irradiation-induced defects and defect-related effects on the electrical characteristics of n-type GaN-based materials and devices . . . While the irradiation-induced effects on device threshold voltage could be regarded as relatively benign (taking into account that the irradiation levels employed in this study are equivalent to more than 60 years exposure at the average ionising dose rate levels present in space missions), the observed device instabilities and the degradation of gate current characteristics are deleterious effects which will have a significant impact on the performance of AlGaN/GaN HEMTs operating in radiation environments at low temperatures, a combination of conditions which are found in spaceborne electronic systems.
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Kuan, Hrong, and 管鴻. "Characterization of Compound Semiconductors and High Electron mobility Transistor Grown by All Metal-Organic Sources with Modulation Spectroscopy." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/22662813590261799986.
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博士國立成功大學
電機工程研究所
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In this dissertation, the GaAs,InP and,InxGa1-xAs epi- layers and high electron mobility transistor (HEMT) have been successfully grown by home-made low pressure metal- organic chemical vapor deposition (MOCVD) system with tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) as the group V sources. Symmetry forbidden transitions such as 1C-2 H and 2C-1H have often been observed from modulation spectra. The electric field in the In0.23Ga0.77As/GaAs QW is increased by applying a reverse bias voltage. The fields in GaAs calculated from the FKO are 3.19×10E4,3.37×10E4, and 3.45×10 E4 V/cm at Vbias=0, 10, and 20 V, respectively. The amount of shifting for 1C-1H, 1C-2H, and 2C-1H transitions are about 16, 17, and 23 meV, respectively or Vbias being changed from 0 to 20 V. The GaAs transition shows FKO.We believe that FKO is attributed to the built-in electric field near GaAs/InGaAs interface region. Using the least-squares fits to the phonon- coupling model, we can obtain the value of amounts 8.4 , 8.7 and 9.1 meV, respectively. The strength of the eletroptical phonon coupling are 6.8, 6.8 and 6.9 meV, while the energy of the longitudinal optical phonon(Eph) are 34,35 and 36 meV, respectively. of 1.5 V,the device has a peak transconductance of 175 mS/mm and 253 mS/mm,respectively.These characteristics show that the transistor possesses excellent saturation and linear regions, allowing the transistor to be pinched off completely at a low gate source bias of -1V (x=0.3) and -1.6 V (x=0.4). The peaks around 1.035 and 1.06 eV are related to the 2DEG signal. From the position of these FKO maxima we calculated the built-in electric field E. We determined the built-in field E, which gives a value of 20.6×10E4 V/cm at indium composition 0.3 and 22.6×10E4 V/cm at indium composition 0.4.