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1
Grigioni, I. "DEVELOPMENT OF PHOTOCATALYTIC MATERIALS FOR SOLAR LIGHT CONVERSION INTO FUELS." Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/333066.
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Solar light possesses a large amount of energy. The sun provides to our planet an intense flux of high energetic photons capable to promote extremely up-hill reactions, such as the photosynthetic fixation of CO2 in biological systems. This energy flow drives life on Earth.
My PhD thesis is focused on solar driven conversion processes. While in the first year I principally investigated the photocatalytic reduction of CO2 with TiO2-based materials. In the second year I started to explore new promising visible light harvesting materials and in particular I worked on CdSe quantum dots synthesis and on their use as photocatalysts for hydrogen production under visible light, with special interest on the size dependent recombination of the photogenerated. Finally, during my stage by Professor Kamat’s laboratory at Notre Dame University (Indiana, US), I started to work on the use of WO3/BiVO4 heterojunction photoanodes, for photoelectrocatalytic applications, and especially on charge carriers dynamics through transient absorption spectroscopy measurements.
A short overview of the main themes treated during my PhD is outlined below.
1st year
1. Photocatalytic tests on TiO2 based materials in the photoassisted reactions of CO2 reduction and steam reforming of methanol, as a part of the research project FotoRiduCO2 PON01_02257.
2nd year
2. Synthesis and characterization of CdSe quantum dots with different size and their application in photocatalytic H2 production under visible light irradiation.
3. Preparation of WO3, BiVO4 and WO3/BiVO4 photoanodes for photoelectrochemical water splitting application and their study with transient absorption techniques.
3rd year
4. Preparation and characterization through femtosecond transient absorption spectroscopy of BiVO4 and WO3/BiVO4 films with variable BiVO4 thickness. The use of different pump energy allowed to suggest a new optical transition model that accounts for the electron transfer paths between the two oxides. Photoelectrochemical experiments validate the proposed model.
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Böhme, Christoph. "Dynamics of spin-dependent charge carrier recombination." [S.l.] : [s.n.], 2003. http://archiv.ub.uni-marburg.de/diss/z2003/0183.
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Yamamoto, Shunsuke. "Charge Carrier Dynamics in Polymer Solar Cells." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157616.
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Solowan, Hans-Michael [Verfasser], and Ulrich T. [Akademischer Betreuer] Schwarz. "Charge carrier dynamics in InGaN quantum wells: stimulated emission depletion and lateral charge carrier motion." Freiburg : Universität, 2016. http://d-nb.info/1119452694/34.
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D'Souza, Arvind Inacib. "Picosecond dynamics of charged carriers in amorphous semiconductors /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260135357755.
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Lambright, Scott. "Ultrafast Charge Carrier Dynamics in Au/Semiconductor Nanoheterostructures." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1404741549.
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Rueda, Delgado Diana Paola. "Charge carrier dynamics and interfaces in perovskite solar cells." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667466.
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Organometal halide perovskites for solar cells are hybrid semiconductors that recently have caught the attention of the scientific community due to its excellent performance and attractive optical properties. Since then, they have been used in solar cells, LEDs, and lasers, although the mechanisms by which such good performances are obtained are not known completely.
This dissertation presents a study of the optical characteristics of perovskites for thin-film solar cells. Due to their small thickness, the morphology of the layer is sensitive to manufacturing parameters. In this way, the manufacturing process is optimized, trying to improve its characteristics.
Among the challenges perovskites pose for implementation, the lack of stability during operation is one of the most relevant. Therefore, in this dissertation, the reasons for stability losses are also studied. For this purpose, interlayers are used, which introduce changes in the interface of the perovskite with the electron extraction layer, and with the initial purpose of reducing the hysteresis in the current-voltage curve. In addition to reducing it, they stabilize the power extracted from the solar cell under illumination. The effects of degradation on the characteristics of solar cells allow the identification of their origins and propose a solution to avoid or delay damage to the perovskite layer. With this in mind, it is established that the problem of stability does not only lie within the perovskite layer but also in the contact between the layers and in the charge transport within the perovskite solar cell. Careful control of these interfaces, then, facilitates the achievement of stable performances and long lifetimes of the perovskite solar cells.Las perovskitas organometálicas de haluros para celdas solares son un tipo de semiconductor híbrido que recientemente ha atrapado la atención de la comunidad científica debido a su excelente desempeño y atractivas propiedades ópticas. Desde entonces, han sido utilizadas en celdas solares, LEDs y lasers, a pesar de que los mecanismos por los cuales se obtienen tan buenos desempeños no son completamente conocidos. Con esta disertación se presenta un estudio sobre las características ópticas de la perovskitas para su utilización en celdas solares de películas delgadas. Debido a su delgado grosor, la morfología de la capa es sensible a los parámetros de fabricación. De manera que se optimiza el proceso de fabricación tratando de mejorar sus características. Entre los retos que presentan las perosvkitas para su implementación, la falta de estabilidad durante su funcionamiento es uno de los más relevantes. Entonces en este dissertationo se estudian también las razones por las que se presenta pérdidas de estabilidad. Para esto se utilizan entrecapas, que introducen cambios en la interfaz de la perovksite con la capa extractora de electrones, y con el propósito inicial de reducir la histéresis en la curva de corriente-voltaje. Además de reducirlo, estabilizan la potencia extraída de la celda solar bajo iluminación. Los efectos de la degradación en las características de las celdas solares nos permiten identificar sus orígenes y presentar propuestas para evitar o retardar los daños a la capa de perovskita. Teniendo esto en cuenta, podemos establecer que el problema de la estabilidad no radica sólo dentro de la perovskita, pero también en el contacto entre las capas y en el transporte de carga dentro de la celda solar de perovskita. El control cuidadoso de estas interfaces, entonces, permite la obtención de un rendimiento estable y una vida larga del dispositivo.
Organometallhalogenid-Perowskite sind hybride Halbleiter, die in jüngster Zeit aufgrund ihrer hervorragenden Halbleitereingeschaften und attraktiven optischen Eigenschaften die Aufmerksamkeit der Wissenschaft auf sich gezogen haben. Seitdem wurde die exzellente Eignung dieser Materialklasse für verschiedenste opto-elektrische Anwendungen wie z.B. Solarzellen, LEDs und Lasern unter Beweis gestellt. Die physikalischen Mechanismen, die die Grundlage für diese einzigartigen, qualitativ Hochwertigen Eigenschaften bilden, sind jedoch noch weitgehend unbekannt. Dieses Manuskript stellt eine Studie über die optischen Eigenschaften von Perowskitfilmen für den Einsatz in Dünnschichtsolarzellen dar, die mit dem Spin-Coating-Verfahren hergestellt wurden. Aufgrund des geringen Dicken der Perowskitschichten ist deren Morphologie empfindlich gegenüber kleinen Variationen der Fertigungsparameter. Deshalb muss der Herstellungsprozess durch Feinjustierung dieser Parameter optimiert werden, um hocheffiziente Solarzellen herzustellen. Eine der größten Herausforderungen für die Kommerzialisierung der Perowskitphotovoltaik ist neben der Herstellung durch die mangelnde Stabilität des Wirkungsgerades während des Betriebs gegeben. Daher werden in der vorliegenden Arbeit zusätzlich die Gründe für diese Stabilitätsverluste untersucht. Zu diesem Zweck werden zusätzliche Nanoschichten zwischen der Perowskit- und der Elektronenextraktionsschicht appliziert, die nicht nur eine Reduzierung der Hysterese in der Strom-Spannungskurve bewirken, sondern die Leistung der Solarzelle unter Sonneneinstrahlung stabilisieren. Der Vergleich der Stabilität von Solarzellen mit und ohne zusätzlichen Zwischenschichten ermöglicht Rückschlüsse auf die Ursache der Degradationsmechanismen. Ein Hauptresultat dieser Stabilitäts- bzw. Degradationsstudie ist die Tatsache, dass ein Großteil des beobachteten Effizienzverlustes nicht durch die Perowskitdegradation innerhalb des Filmes, sondern vielmehr durch die Instabilität der Grenzflächen des Perowskits mit den Extraktionsschichten zustande kommt. Die Grenzflächendegradation erzeugt eine Barriere für den Ladungstransport durch die Erhöhung der lokalen „Trap-Dichte“. Basierend auf dieser Erkenntnis eröffnet die sorgfältige Modifikation der Grenzflächen innerhalb der Solarzelle vielfältige Möglichkeiten, um eine stabile Betriebsleistung der Solarzelle über längere Zeiten durch Vermeidung bzw. Verzögerung der Degradation zu erzielen
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Gilmore, Rachel Hoffman. "Charge carrier dynamics in lead sulfide quantum dot solids." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/115015.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, September 2017.Cataloged from PDF version of thesis. "February 2018." Handwritten on title page: [September 2017].
Includes bibliographical references (pages 105-117).
Quantum dots, also called semiconductor nanocrystals, are an interesting class of materials because their band gap is a function of the quantum dot size. Their optical properties are not determined solely by the atomic composition, but may be engineered. Advances in quantum dot synthesis have enabled control of the ensemble size dispersity and the creation of monodisperse quantum dot ensembles with size variations of less than one atomic layer. Quantum dots have been used in a variety of applications including solar cells, light-emitting diodes, photodetectors, and thermoelectrics. In many of these applications, understanding charge transport in quantum dot solids is crucial to optimizing efficient devices. We examine charge transport in monodisperse, coupled quantum dot solids using spectroscopic techniques explained by hopping transport models that provide a complementary picture to device measurements. In our monodisperse quantum dot solids, the site-to-site energetic disorder that comes from size dispersity and the size-dependent band gap is very small and spatial disorder in the quantum dot superlattice often has a greater impact on charge transport. In Chapter 2, we show that improved structural order from self-assembly in monodisperse quantum dots reduces the interparticle spacing and has a greater impact than reduced energetic disorder on increasing charge carrier hopping rates. In Chapter 3, we present temperature-dependent transport measurements that demonstrate again that when energetic disorder is very low, structural changes will dominate the dynamics. We find increasing mobility with decreasing temperature that can be explained by a 1-2 Å contraction in the edge-to-edge nearest neighbor quantum dot spacing. In Chapter 4, we study optical states that are 100-200 meV lower in energy than the band gap. Because we work with monodisperse quantum dots, we are able to resolve this trap state separately from the band edge state and study its optical properties. We identify the trap state as dimers that form during synthesis and ligand exchange when two bare quantum dot surfaces fuse. The findings of this thesis point to the importance of minimizing the structural disorder of the coupled quantum dot solid in addition to the energetic disorder to optimize charge carrier transport.
by Rachel Hoffman Gilmore.
Ph. D.
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Peckus, Domantas. "Ultrafast exciton and charge carrier dynamics in nanostructured molecular layers." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20131220_150447-81409.
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Due to their unique properties organic semiconductors may be used for various applications in organic optoelectronic devices: light emitting devices, lasers, field-effect transistors, photovoltaic cells and etc. Despite high perspectives of organic semiconductors they are still upstaged by their inorganic counterparts. Development of organic electronics requires better understanding of electrooptical properties of organic semiconductors and relationships between their structure and functions.
The main goal of this thesis is a detailed investigation of ultrafast exciton and charge carrier processes in pure organic semiconductors and their blends with fullerene derivatives. Investigated organic or silicon organic semiconductors were poly-di-n-hexylsilane (PDHS), polyfluorenes F8BT and PSF-BT, merocyanine MD376. C60 fullerene and its derivative PCBM were used in blends. Ultrafast transient absorption, fluorescence, and integral mode photocurrent measurements were used for investigations.
The investigation of PDHS nanocomposites revealed that PDHS incorporation into nanopores can be used for improvement of fluorescence properties.
Formation of intramolecular charge transfer state was proposed for PSF-BT neat films. Charge transfer scheme of the formation of long-lived charge pair state in PSF-BT/PCBM blend was presented.
The charge pair and free charge carrier generation scheme in merocyanine blends with fullerene derivatives were discussed in detail.
Analysis of measurement... [to full text]Dėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių. Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai. PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui. Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose. Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą]
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Strothkämper, Christian [Verfasser]. "Charge Carrier Dynamics in Thin Film Solar Cells / Christian Strothkämper." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1037725832/34.
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Tyagi, Pooja. "Surface effects on charge carrier dynamics in semiconductor quantum dots." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117122.
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Due to the large surface-to-volume ratio of quantum dots, their surface conditions play a significant role in determining their electronic and optical properties. In this thesis, we show that the presence of surface states modifies the optical selection rules in quantum dots and enhances the rate of surface charge trapping. These surface-induced effects have profound impact on the measurement of multiexciton recombination and carrier multiplication processes. Specifically, in transient absorption studies, surface states result in additional decay timescales which may be misattributed to multiexciton recombination processes. Additionally, they lead to large "apparent" carrier multiplication yields even under conditions where it is forbidden by energy conservation. The surface-dependent transient absorption studies presented in this work suggest ways to identify and minimize the undesirable surface-induced signals. Interestingly, surface-induced processes also result in significant electrostatic effects. We show that due to the piezoelectric nature of wurtzite CdSe quantum dots, the strong electric field created by surface charge trapping can drive coherent acoustic phonons in these systems. We further show that the amplitude of this piezoelectric response can be controlled by altering the surface conditions of the quantum dot. Finally, we theoretically investigate the effect of multiple surface layers on carrier localization in nanostructures. We find that in a core/barrier/shell configuration, layered nanostructures offer independent control over electron and hole wave functions. These results suggest design principles for wave function engineering in potential quantum dot applications in light emitting devices, photovoltaics and optical amplification.En raison du rapport surface volume élevé des points quantiques, les conditions de leurs surfaces jouent un rôle important dans la détermination des propriétés électroniques et optiques. Dans cette thèse, nous démontrons que la présence d'états de surface modifie les règles de sélection optiques dans les points quantiques et améliore le taux de piégeage des charges sur la surface. Ces effets induits par la surface ont un impact profond sur la mesure de la recombinaison de mutliexcitons et les processus de multiplication de porteurs. Plus précisément, en poursuivant des études d'absorption transitoires, nous démontrons que la présence des états de surface se traduits dans des délais de décroissance supplémentaires qui peuvent être attribuées à tort à des processus de recombinaison de multiexcitons. En outre, ils conduisent èa de grandes rendements apparents de multiplication des porteurs, même dans des conditions oèu il est interdit par la conservation de l'énergie. Les études d'absorption transitoires de la surface présentés dans ce travail suggèrent des moyens d'identifier et de réduire les signaux indésirables induits par la surface.Fait intéressant, les processus induites par la surface entraînent aussi des effets électrostatiques significatifs. Nous démontrons qu'en raison de la nature piézoélectrique des points quantiques de wurtzite CdSe, le fort champ électrique créé par le piégeage de charges sur la surface peut conduire des phonons acoustiques cohérents dans ces systèmes. En plus, nous démontrons que l'amplitude de cette réponse piézo-électrique peut être contrôlé en modifiant les conditions de la surface du point quantique. Enfin, nous avons étudié théoriquement l'effet sur la localisation des porteurs de strates multiples de surface dans les nanostructures. Nous constatons que dans une configuration de base/barrière/coque, les nanostructures stratifiées offrent un contrôle indépendant sur la fonction d'onde des électrons et trous. Ces résultats suggèrent des principes de conception pour l'ingénierie de fonction d'onde dans des applications potentielles de points quantiques dans les dispositifs émettant de la lumière, l'énergie photovoltaïque et de l'amplification optique.
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Pendlebury, Stephanie R. "Charge carrier dynamics in hematite photoanodes for solar water oxidation." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9952.
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Although the field of solar water splitting is now forty years old, in recent years there has been an upsurge of research in this area, with the aim of using sunlight to produce hydrogen cheaply and efficiently. Hematite (α-Fe2O3) is of particular interest as a photoanode material for solar water splitting, due to its optimum band gap (2.0-2.2 eV) and visible light absorption and stability. Various modifications – including nanostructuring and doping – have been investigated as routes to improved efficiencies, thought to be limited by long visible light absorption depths, low charge carrier mobilities and slow hole-transfer kinetics. Additionally, an anodic applied bias is required for water oxidation to occur on hematite. Improved understanding of the role of applied bias and the processes limiting the performance of hematite photoanodes will lead to more directed routes to photoanode architectures with increased efficiencies. This Thesis describes the results of transient absorption spectroscopy studies, in conjunction with photoelectrochemical measurements, of hematite photoanodes. Transient absorption spectroscopy on microsecond-second timescales allows direct monitoring of the recombination, trapping and reaction of photogenerated holes, both in isolated hematite films, and in photoanodes in a fully functional photoelectrochemical cell. Transient photocurrent measurements probe electron extraction from the photoanode on microsecond-millisecond timescales. The charge carrier dynamics are found to be strongly dependent on the electron density, which is controlled by applied electrical bias. The photocurrent generated is found to correlate with the population of long-lived holes, determined by the kinetics of electron-hole recombination. Generally, effects which lower electron density result in retarded electron-hole recombination kinetics, increasing the population of long-lived holes and hence increasing the photocurrent. Following an introduction and review of the literature, the first results chapter reports that the effect of a positive applied bias is to retard the otherwise dominant electron-hole recombination, increasing the lifetime of photogenerated holes such that water oxidation can occur. The relative timescales of recombination, electron extraction and water oxidation as a function of applied bias are discussed in the following chapter, in conjunction with the results of excitation density studies. The third results chapter compares the charge carrier dynamics in photoanodes with different nanomorphologies. The fourth results chapter discusses the effect of an energetic trap state on charge carrier dynamics, while the effects of surface treatment with cobalt, which is shown to retard recombination at low applied bias, is reported in the final results chapter. Overall conclusions are drawn and the implications of these for photoelectrode design are discussed.
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Karlsen, Peter. "Terahertz spectroscopy of charge-carrier dynamics in one-dimensional nanomaterials." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/33086.
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One-dimensional (1D) nanomaterials are of great importance for a number of potential applications. However, in order to realize this potential a thorough understanding of the charge-carrier dynamics in these materials is required, since these largely determine the optoelectronic properties of the materials in question. This thesis investigates the charge-carrier dynamics of two 1D nanomaterials, single-walled carbon nanotubes (CNTs) and tungsten-oxide nanowires (WOxNWs), with the goal of better understanding the nature of their optoelectronic responses, and how nanomaterial geometry and morphology influence these responses. We do this using terahertz time-domain spectroscopy (THz-TDS) and optical pump - terahertz probe time-domain spectroscopy (OPTP). Firstly, we discuss how to properly analyse and interpret the data obtained from these experiments when measuring 1D nanomaterials. While the data obtained from THz-TDS is fairly straight-forward to analyse, OPTP experimental data can be far from trivial. Depending on the relative size of the sample geometry compared to the probe wavelength, various approximations can be used to simplify the extraction of their ultrafast response. We present a general method, based on the transfer matrix method, for evaluating the applicability of these approximations for a given multilayer structure, and show the limitations of the most commonly used approximations. We find that these approximations are only valid in extreme cases where the thickness of the sample is several orders of magnitude smaller or larger than the wavelength, which highlight the danger originating from improper use of these approximations. We then move on to investigate how the charge-carrier dynamics of our CNTs is influenced by nanotube length and density. This is done through studying the nature of the broad THz resonance observed in finite-length CNTs, and how the nanotube length and density affects this resonance. We do this by measuring the conductivity spectra of thin films comprising bundled CNTs of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. From this we show that the observed temperature-induced changes in the terahertz conductivity spectra depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS2 nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak. Next, we investigate the conflicting reports regarding the ultrafast photoconductive response of films of CNTs, which apparently exhibit photoconductivities that can vastly differ, even in sign. Here we observe explicitly that the THz photoconductivity of CNT films is a highly variable quantity which correlates with the length of the CNTs, while the specific type of CNT has little influence. Moreover, by comparing the photo-induced change in THz conductivity with heat-induced changes, we show that both occur primarily due to heat-generated modification of the Drude electron relaxation rate, resulting in a broadening of the plasmonic resonance present in finite-length metallic and doped semiconducting CNTs. This clarifies the nature of the photo-response of CNT films and demonstrates the need to carefully consider the geometry of the CNTs, specifically the length, when considering them for application in optoelectronic devices. We then move on to consider our WOxNWs. We measure the terahertz conductivity and photoconductivity spectra of thin films compromising tungsten-oxide (WOx) nanowires of average diameters 4 nm and 100 nm, and oxygen deficiencies WO2.72 and WO3 using THz-TDS and OPTP. From this we present the first experimental evidence of a metal-to-insulator transition in WOx nanowires, which occurs when the oxygen content is increased from x=2.72 -> 3 and manifests itself as a massive drop in the THz conductivity due to a shift in the Fermi level from the conduction band down into the bandgap. Furthermore we present the first experimental measurements of the photoexcited charge-carrier dynamics of WOx nanowires on a picosecond timescale and map the influence of oxygen-content and nanowire diameter. From this we show that the decay-dynamics of the nanowires is characterized by a fast decay of < 1 ps, followed by slow decay of 3-10 ps, which we attribute to saturable carrier trapping at the surface of the nanowires.
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Juang, Agnes Okumura Mitchio Lewis Nathan Saul. "Effects of surface modification on charge-carrier dynamics at semiconductor interfaces /." Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-08062002-192958.
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Hempel, Hannes [Verfasser]. "Investigation of Charge Carrier Dynamics in Novel Photovoltaic Materials / Hannes Hempel." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1205736069/34.
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Rivett, Jasmine Pamela Helen. "Charge carrier dynamics of lead halide perovskites probed with ultrafast spectroscopy." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275095.
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In this thesis, we investigate the nature of charge carrier generation, relaxation and recombination in a range of lead halide perovskites. We focus on understanding whether the photophysical behaviour of these perovskite materials is like that of highly-ordered inorganic crystalline semiconductors (exhibiting ballistic charge transport) or disordered molecular semiconductors (exhibiting strong electron-phonon coupling and highly localised excited states) and how we can tune these photophysical properties with inorganic and organic additives. We find that the fundamental photophysical properties of lead halide perovskites, such as charge carrier relaxation and recombination, arise from the lead halide lattice rather than the choice of A-site cation. We show that while the choice of A-site cation does not affect these photophysical properties directly, it can have a significant impact on the structure of the lead halide lattice and therefore affect these photophysical properties indirectly. We demonstrate that lead halide perovskites fabricated from particular inorganic and organic A-site cation combinations exhibit low parasitic trap densities and enhanced carrier interactions. Furthering our understanding of how the photophysical properties of these materials can be controlled through chemical composition is extremely important for the future design of highly efficient solar cells and light emitting diodes.
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Ma, Yimeng. "Dynamics of charge carriers in bismuth vanadate photoanodes for water splitting using solar energy." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/38559.
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This thesis described an investigation of charge carrier dynamics in dense, flat bismuth vanadate (BiVO4) photoanodes using transient absorption spectroscopy and photoelectrochemical measurements including transient photocurrents. Transient absorption spectroscopy was employed to probe directly the photogenerated charge carrier population change as a function of time from microsecond (μs) to second (s) timescales. Transient photocurrent measurements were used to monitor charge extraction under chopped light conditions. Photo-induced absorption spectroscopy was employed to investigate charge carriers under working photo-electrochemical (PEC) conditions. The transient absorption signals due to photogenerated holes in BiVO4 were determined through using electron/hole scavengers and applied electrical bias in a complete photoelectrochemical cell. In 'un-doped' BiVO4, photogenerated holes were found to absorb from 500 nm to 900 nm. The dynamics of photogenerated holes were studied as a function of applied potential and excitation intensity. The population of long-lived (milliseconds-seconds) holes increased with increasing the width of space charge layer as a function of applied potential. A recombination process in kinetic competition with water oxidation on these long timescales was found to limit the photocurrent amplitude and onset potential in un-doped BiVO4 photoanodes. Using transient photocurrent measurements, this recombination process was identified as recombination of surface-accumulated holes with electrons from the bulk of the semiconductor (back electron/hole recombination). Doping molybdenum (MoVI) in un-doped BiVO4 has been reported to be an effective method to increase photocurrent amplitude. Impedance measurements were carried out to determine the donor density increased by the presence of MoVI doping. The increased donor density limited efficient generation of the space charge layer to retard fast recombination on microseconds to milliseconds timescales, thus limiting the long-lived hole yield under modest applied potentials. MoVI dopants were shown to improve the electron transport determined by front/back side illumination in PEC and transient absorption spectroscopy (TAS) measurements. Cobalt phosphate (CoPi) surface-modified un-doped BiVO4 photoanodes were also studied using transient absorption spectroscopy and transient photocurrent measurements. Transient absorption spectra of CoPi-modified BiVO4 were similar to those of unmodified BiVO4, and the kinetics on milliseconds to seconds did not change in the presence of CoPi surface modification. Both results indicated that photogenerated holes in BiVO4 rather than CoPi species were monitored by transient absorption spectroscopy. However, the negative shift of photocurrent onset and increased photocurrent could be explained by efficient suppression of back electron/hole recombination in BiVO4 photoanodes. In terms of the function of CoPi water oxidation catalysts on BiVO4, photo-induced absorption (PIA) was employed to further study the CoPi/BiVO4 system. CoPi species oxidised by BiVO4 holes were observed in PIA measurements due to the high extinction coefficient of oxidised CoPi and significant hole accumulation generated by continuous illumination. However, these oxidised CoPi species did not appear to drive catalytic water oxidation, as evidenced by results from spectroelectrochemical measurements of CoPi/FTO electrodes; water oxidation still occurred via BiVO4, consistent with the transient absorption results. Therefore, I concluded that in the CoPi/BiVO4 system, CoPi did not act as a catalyst, although hole transfer to CoPi can take place.
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Kaveh, Baghbadorani Masoud. "Emission and Dynamics of Charge Carriers in Uncoated and Organic/Metal Coated Semiconductor Nanowires." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470754655.
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Polizzotti, Alex J. "Improving charge carrier dynamics in tin (II) sulfide through targeted defect engineering." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118730.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 145-151).
Tin sulfide is an emerging material for photovoltaics, with the potential for highthroughput manufacturing to combat climate change by displacing fossil fuel generation. However, device efficiencies for SnS have plateaued at below 5% efficiency, making them as yet insufficient for commercial production. Low minority carrier lifetimes of <100 ps have been shown to be the root cause of this low performance, and carrier lifetimes >1 ns are predicted to enable >10%-efficient devices. In this thesis work, I employed defect modeling to identify the most recombination-active point defects: the extrinsic Fe[subscript Sn], Co[subscript Sn], and Mo[subscript Sn] and the intrinsic V[subscript S]. I grew SnS single crystals and demonstrated that by suppressing these defects during growth, I could improve minority carrier lifetime to >1 ns. I built a unique, highly customized close-spaced sublimation furnace to translate these learnings to device-relevent thin films. By designing a system for metal-free, sulfur-rich growth at high temperature, I was able to achieve >10 ns carrier lifetimes in SnS thin films. I fabricated initial devices with this high-purity material. While none of these devices exceed the record efficiencies, they are primarily limited by poor device construction and a resulting low fill factor, and further improvements are expected to unlock the full potential of this new, improved SnS material.
by J. Alex Polizzotti.
Ph. D.
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Pettinger, Natasha. "The Charge-Carrier Dynamics and Photochemistry of CeO2 Nanoparticles." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1565869748067293.
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Pintossi, C. "CARBON-BASED HYBRID PLATFORMS FOR NOVEL PHOTOVOLTAIC DEVICES: BURIED INTERFACE CHEMISTRY AND CHARGE CARRIERS DYNAMICS." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/362241.
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Current photovoltaic (PV) market is strongly dominated by an intense use of silicon. Although it is the second most abundant element on the Earth crust, after oxygen, Si is never present in its pure form but always bounded with other elements, and relatively complex and expensive purification procedures are needed in order to have clean, crystalline and optimally doped pure silicon.
This issue, joined with the ever-increasing demand of clean Si by almost all the technological modern applications, led scientists all over the world to look for suitable alternatives.
One of the most promising options, is to try to substitute silicon with carbon, essentially for two reasons: (i) pure C not only exists in nature but can also be obtained and purified through easy and low-cost processes, (ii) carbon can behave as a metal or a semiconductor without being doped, depending only on the particular allotrope.
Moreover, carbon allotropes capability of arranging in various geometry allows C-based materials to assume different dimensionality, starting from the quasi zero-dimensional fullerene to three-dimensional diamonds. This makes carbon nanomaterials excellent candidate for a wide range of electrical and technological devices, offering the possibility to chose the suitable allotropes depending on the particular task that is needed to be fulfilled.
For photovoltaic application, a semiconducting material which can provide dissociation sites for excitons is necessary. To accomplish this role, the mono-dimensional form of C, carbon nanotubes (CNTs), revealed to be a perfect substitute of p-type silicon, on one side of the junction because CNTs are naturally p-doped in air.
Moreover, thanks to their peculiar geometry and extraordinary electrical conductivity, they are able to provide excellent transport path for the dissociated carriers with a very good transparency (which allows a relevant amount of incident light to reach the depletion region).
In the first chapter of this thesis, carbon nanotubes will be introduced, emphasizing the properties which make this nanostructured materials optimal for PV applications. Then, the different types of carbon/silicon heterojunctions will be analyzed, starting from the classical semiconductor theory, to a more complex and realistic model. At the end of the chapter CNTs solar cells state of the art will be presented, highlighting the open questions at which this thesis is aimed to answer.
The experimental techniques, such as angle-resolved X-rays photoelectron spectroscopy (AR-XPS) and transient reflectivity (TR) measurements, used to reach this goal will be presented in Chapter 2, together with the description of the manufacturing processes that yielded to the creation of three different series of PV devices, with an improvement of the efficiency from 0.1% to 12.2% in three years.
In the third chapter, we will show how the complex buried interface between CNTs and Si can be investigated and modelled by means of photoelectron spectroscopy techniques. A complex oxide interface, composed by silicon dioxide and non-stoichiometric silicon oxide, has been unveiled and possible effects on the power conversion efficiency of PV devices are outlined.
A systematic study on the chemical and physical properties of the buried interface will be presented in Chapter 4. Oxides have been alternatively removed and regrown using suitable acids and the effects on the PV performances will be discussed in detail in this chapter. The doping effects of acids on the carbon nanotubes will also be investigated through Raman spectroscopy.
Acid effects on the heterojunctions will be unambiguously shown by the XPS measurements, and the matching of these data with the electrical PV measurements allows us to discuss the nature of the heterojunction in more detail.
In order to properly address the operation mechanism of these devices, which can be either a conventional p-n or a metal-insulator-semiconductor (MIS) junction, the dynamics of charge transfer processes at the interface will be investigated in Chapter 5 with time-resolved pump-probe reflectivity measurement.
The aim is to find a correlation between the thickness of the buried SiOxlayer and the carriers photogeneration and transport, comparing the device electrical parameter with the ultrafast behavior, analyzed by time-resolved reflectivity.
These last findings, along with several improvements in the CNTs dispersion and deposition, have led to the creation of optimized third-series solar cells with a record efficiency of 12.2%, which will be fully characterized at the end of this last chapter through a combination of suitable experimental techniques, in order to highlight the factors which contributed to this huge jump in the power conversion efficiency. The stability in time of this optimized PV devices will finally be discussed.
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Eads, Calley N., Dmytro Bandak, Mahesh R. Neupane, Dennis Nordlund, and Oliver L. A. Monti. "Anisotropic attosecond charge carrier dynamics and layer decoupling in quasi-2D layered SnS2." NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/626188.
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Strong quantum confinement effects lead to striking new physics in two-dimensional materials such as graphene or transition metal dichalcogenides. While spectroscopic fingerprints of such quantum confinement have been demonstrated widely, the consequences for carrier dynamics are at present less clear, particularly on ultrafast timescales. This is important for tailoring, probing, and understanding spin and electron dynamics in layered and two-dimensional materials even in cases where the desired bandgap engineering has been achieved. Here we show by means of core-hole clock spectroscopy that SnS2 exhibits spin-dependent attosecond charge delocalization times (tau(deloc)) for carriers confined within a layer, tau(deloc) < 400 as, whereas interlayer charge delocalization is dynamically quenched in excess of a factor of 10, tau(deloc) > 2.7 fs. These layer decoupling dynamics are a direct consequence of strongly anisotropic screening established within attoseconds, and demonstrate that important two-dimensional characteristics are also present in bulk crystals of van der Waals-layered materials, at least on ultrafast timescales.
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Kampfrath, Tobias. "Charge carrier dynamics in solids and gases observed by time resolved terahertz spectroscopy." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2006/250/index.html.
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Karakus, Uzuner Melike [Verfasser]. "Charge carrier dynamics in hybrid systems for solar energy conversion / Melike Karakus Uzuner." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1132608430/34.
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Cooney, Ryan. "Charge carrier dynamics and the development of optical gain in semiconductor quantum dots." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86867.
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State-resolved pump/probe measurements with femtosecond temporal resolution were made to examine the size dependent charge carrier dynamics of strongly confined CdSe quantum dots. Following optical excitation, relaxation in the conduction band is shown to be consistent with the expectations of an Auger mediated process. In the valence band, the presence of a previously unobserved relaxation mechanism is detected. This mechanism is associated with non-adiabatic interactions with the surface ligands. The quantitative nature of these measurements, resulting from the explicit investigation of state-to-state transition rates, allowed for the development of a unified picture of exciton relaxation in these materials. Here the total transition rate associated with the charge carriers is composed of a manifold of different contributions, each with a distinct size dependence.These state-resolve methods were further applied to investigate the development of optical gain in CdSe quantum dots. It was observed that the capacity of these systems to achieve the regime of optical gain has a pronounced dependence on the initially prescribed excitonic state. In general, as the energy of the initial state was increased it was progressively more difficult to achieve optical gain due to the impeding influence of state dependent multiexcitonic interactions. This explains the inability of prior research which used fixed wavelength excitation sources to demonstrate optical gain in small particles. By maintaining the identity for the pumped state in different particle sizes, the long standing prediction that quantum dots would be a universal gain medium was recovered. In addition, evidence for the capacity of specific higher order multiexcitonic interactions to manipulate the resulting optical gain spectrum was provided.
Des mesures pompe/sonde résolues en états quantiques de résolutions temporelles de l'ordre du femtoseconde ont été effectuées pour examiner la dynamique, dépendante de la taille, des transporteurs de charges de points quantiques de CdSe fortement confinés. Après l'excitation optique, la relaxation de la bande de conduction s'effectue par le mécanisme Auger, tel que prédit, alors que dans la bande de valence la présence d'un mécanisme de relaxation précédemment inobservé est détectée. Ce mécanisme est associé aux interactions non-adiabatiques avec les ligands de surface. La nature quantitative de ces mesures, résultant d'une recherche explicite sur les taux de transition d'état-à-état, a permis de développer un portrait d'ensemble de la relaxation d'exciton pour ces matériaux. Dans ce système, le taux de transition associé aux porteurs de charge se compose de différentes contributions, chacune ayant une dépendance de taille distincte.
Ces méthodes résolues en états quantiques ont été également appliquées à l'étude du développement du gain optique dans les points quantiques de CdSe. Il a été observé que la capacité de ces systèmes à atteindre le régime du gain optique dépend fortement de l'état excitonique initial. Au fur et à mesure que l'énergie de l'état fondamental fût augmentée, il fùt progressivement plus difficile d'obtenir un gain optique à cause de l'influence des interactions multiexcitoniques, dépendantes des états. Ceci explique donc l'incapacité des études antérieures, ayant utilisées des sources fixes d'excitation de longueur d'onde, à démontrer le gain optique des petites particules. La prévision émise antérieurement selon laquelle les points quantiques seraient un médium de gain universel a été confirmée en conservant l'identité pour l'état pompé dans des tailles de particules différentes. La capacité des interactions multiexcitoniques d'ordres spécifiques supérieures à manoeuvrer le gain optique résultant a aussi été prouvée.
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Cheng, Yuan-Chung Ph D. Massachusetts Institute of Technology. "Quantum dynamics in condensed phases : charge carrier mobility, decoherence, and excitation energy transfer." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34496.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.Vita.
Includes bibliographical references.
In this thesis, we develop analytical models for quantum systems and perform theoretical investigations on several dynamical processes in condensed phases. First, we study charge-carrier mobilities in organic molecular crystals, and develop a microscopic theory that describes both the coherent band-like and incoherent hopping transport observed in organic crystals. We investigate the structures of polaron states using a variational scheme, and calculate both band-like and hopping mobilities at a broad range of parameters. Our mobility calculations in 1-D nearest-neighbor systems predict universal band-like to hopping transitions, in agreement with experiments. Second, motivated by recent developments in quantum computing with solid-state systems, we propose an effective Hamiltonian approach to describe quantum dissipation and decoherence. We then applied this method to study the effect of noise in a number of quantum algorithms and calculate noise threshold for fault-tolerant quantum error corrections (QEC). In addition, we perform a systematic investigation on several variables that can affect the efficiency of the fault-tolerant QEC scheme, aiming to generate a generic picture on how to search for optimal circuit design for real physical implementations.
(cont.) Third, we investigate the quantum coherence in the B800 ring of' of the purple bacterium Rps. acidophila and how it affects the dynamics of excitation energy transfer in a single LH2 complex. Our calculations suggest that the coherence in the B800 ring plays a significant role in both spectral and dynamical properties. Finally, we discussed the validity of Markovian master equations, and propose a concatenation scheme for applying Markovian master equations that absorbs the non-Markovian effects at short times in a natural manner. Applications of the concatenation scheme on the spin-boson problem show excellent agreements with the results obtained from the non-Markovian master equation at all parameter range studied.
by Yuan-Chung Cheng.
Ph.D.
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Cadirci, Musa. "Ultrafast charge dynamics in novel colloidal quantum dots." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/ultrafast-charge-dynamics-in-novel-colloidal-quantum-dots(865aba90-9d60-478d-8f49-ad4785516688).html.
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In this thesis ultrafast exciton dynamics of several colloidal quantum dots have been studied using visible transient absorption spectroscopy. The resultant transient decays and differential transmission spectra were analysed to determine the ultrafast relaxation channels, multiple exciton generation (MEG) efficiency and multi-exciton interactions in the observed materials. All QDs were preliminarily optically characterized using steady state absorption and photoluminescence spectroscopies. In addition, a high repetition infrared femtosecond pump probe experiment was designed and built to detect the picosecond intraband carrier relaxations in quantum dots. Picosecond carrier dynamics of type-II ZnTe/ZnSe and of CuInSe2 and CuInS2 type-I quantum dots were investigated. The common feature of these materials is that they are eco-friendly materials, being alternatives to the toxic Cd- and Pb- based materials. It was found that surface trapping occurred in both cases for electrons in the hot states, and in the minimum of the conduction band for ZnTe/ZnSe core/shell materials. Trion formation was observed in ZnTe/ZnSe core/shell dots at high power and unstirred conditions. The hot and cold electron trapping processes in type-II dots and CuInS2 and CuInSe2 dots shifted, distorted and moderately cancelled the bleach features. In addition, intra-gap hole trapping was observed in CuInS2 and CuInSe2 dots which results in a long decay feature in the recorded transients. MEG competes with Auger cooling, surface mediated relaxation and phonon emission. To enhance the MEG quantum yield, the rival mechanisms were suppressed in well-engineered CdSe/CdTe/CdS and CdTe/CdSe/CdS core/shell/shell and CdTe/CdS core/shell type-II quantum dots. The MEG slope efficiency and threshold for a range of different core size and shell thickness were found to be (142±9)%/Eg and (2.59±0.16)Eg, respectively. The observed threshold was consistent with the literature, whereas, the obtained slope efficiency was about three times higher than the previously reported values. The biexciton interaction energy of the dots stated in the previous paragraph was also studied. To date, time-resolved photoluminescence (TRPL) has been employed to study exciton interactions in type-II quantum dots and large repulsive biexciton interaction energy values between 50-100 meV have been reported. However, unlike the TRPL method, the TA experiment ensures that only two excitons remain in the band edge of the dot. Using this method, large attractive biexciton interaction energies up to ~-60 meV was observed. These results have promising implications regarding enhancing the MEG quantum yield.
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Gieseking, Björn [Verfasser], and Vladimir [Gutachter] Dyakonov. "Excitation Dynamics and Charge Carrier Generation in Organic Semiconductors / Björn Gieseking. Gutachter: Vladimir Dyakonov." Würzburg : Universität Würzburg, 2014. http://d-nb.info/1109750048/34.
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Handloser, Karl Matthias. "Optical investigation of charge carrier dynamics in organic semiconductors and graphene for photovoltaic applications." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-168562.
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Richter, Alexander Florian [Verfasser], and Jochen [Akademischer Betreuer] Feldmann. "Charge carrier dynamics in nontoxic semiconductor quantum dots / Alexander Florian Richter ; Betreuer: Jochen Feldmann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1226092667/34.
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Aytac, Yigit. "Time-resolved measurements of charge carrier dynamics in Mwir to Lwir InAs/InAsSb superlattices." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2039.
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All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as next generation materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential-transmission measurements are used here to demonstrate that "Ga-free" InAs/InAs₁₋xSbx T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements of unintentionally doped MWIR and LWIR InAs/InAs₁₋xSbx T2SLs demonstrate minority carrier (MC) lifetimes of 18.4 µs and 4.5 µs at 77 K, respectively. This represents a more than two order of magnitude increase compared to the 90 ns MC lifetime measured in a comparable MWIR and LWIR InAs/GaSb T2SL. Through temperature-dependent differential-transmission measurements, the various carrier recombination processes are differentiated and the dominant recombination mechanisms identified for InAs/InAs₁₋xSbx T2SLs. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs and potentially bulk Hg₁₋xCdxTe photodetectors.
In addition to carrier lifetimes, the drift and diusion of excited charge carriers through the superlattice layers (i.e. in-plane transport) directly aects the performance of photo-detectors and emitters. All-optical ultrafast techniques were successfully used for a direct measure of in-plane diffusion coeffcients in MWIR InAs/InAsSb T2SLs using a photo-generated transient grating technique at various temperatures. Ambipolar diffusion coefficients of approximately 60 cm²/s were reported for MWIR InAs/InAs₁₋xSbxT2SLs at 293 K.
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Olson, Benjamin Varberg. "Time-resolved measurements of charge carrier dynamics and optical nonlinearities in narrow-bandgap semiconductors." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/2596.
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All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as a next generation source of these materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential transmission measurements are used here to demonstrate that Ga-free InAs/InAsSb T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements at 77 K provided minority carrier lifetimes of 9 μs and 3 μs for an unintentionally doped mid-wave infrared (MWIR) InAs/InAsSb T2SL and InAsSb alloy, respectively; a two order of magnitude increase compared to the 90 ns minority carrier lifetime measured in a comparable MWIR InAs/GaSb T2SL. Through temperature-dependent lifetime measurements, the various carrier recombination processes are differentiated and the dominant mechanisms identified for each material. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs for potentially improved infrared photodetectors.
In addition to carrier lifetimes, the drift and diffusion of excited charge carriers through the superlattice growth layers (i.e. vertical transport) directly affects the performance of photodetectors and emitters. Unfortunately, there is a lack of information pertaining to vertical transport, primarily due to difficulties in making measurements on thin growth layers and the need for non-standard measurement techniques. However, all-optical ultrafast techniques are successfully used here to directly measure vertical diffusion in MWIR InAs/GaSb T2SLs. By optically generating excess carriers near one end of a MWIR T2SL and measuring the transit time to a thin, 2 lower-bandgap superlattice placed at the other end, the time-of-flight of vertically diffusing carriers is determined. Through investigation of both unintentionally doped and p-type superlattices at 77 K, the vertical hole and electron diffusion coefficients are determined to be 0.04±0.03 cm2/s and 4.7±0.5 cm2/s, corresponding to vertical mobilities of 6±5 cm2/Vs and 700±80 cm2/Vs, respectively. These measurements are, to my knowledge, the first direct measurements of vertical transport properties in narrow-bandgap superlattices.
Lastly, the widely tunable two-color ultrafast laser system used in this research allowed for the investigation of nonlinear optical properties in narrow-bandgap semiconductors. Time-resolved measurements taken at 77 K of the nondegenerate two-photon absorption spectrum of bulk n-type GaSb have provided new information about the nonresonant change in absorption and two-photon absorption coefficients in this material. Furthermore, as the nondegenerate spectrum was measured over a wide range of optical frequencies, a Kramers-Kronig transformation allowed the dispersion of the nondegenerate nonlinear refractive index to be calculated.
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Villamil, Franco Carolina. "Ultrafast dynamics of excitons and charge carriers in colloidal perovskite nanostructures studied by time-resolved optical spectroscopies." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASF012.
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Les matériaux semiconducteurs de pérovskite halogénée se sont révélés très prometteurs en raison de leurs propriétés exceptionnelles et de leur capacité d’élaboration à faible coût. Malgré les progrès réalisés, une meilleure compréhension des dynamiques de relaxation et de recombinaison dans ces matériaux photo-actifs est nécessaire afin d’améliorer les performances des dispositifs opto-électroniques. Cette thèse porte sur la relaxation des porteurs de charge/excitons « chauds » après excitation au-dessus de la bande interdite, et la recombinaison Auger advenant après une excitation de forte puissance ou à haute énergie. La spectroscopie de fluorescence résolue en temps et d'absorption transitoire (AT) femtoseconde sont utilisées afin d’étudier les effets du confinement et de la composition sur ces processus, en particulier dans les nanoplaquettes (NPLs) colloïdales de pérovskite bidimensionnelles (2D), dont la synthèse a été développée et optimisée au préalable. Les dynamiques de relaxation ont été étudiées par AT en utilisant une méthode d'analyse globale où l'évolution temporelle des différentes compositions spectrales est modélisée suivant une cinétique de réactions séquentielles. Cette méthode a pu être appliquée afin de décrire efficacement la relaxation progressive dans les nanostructures de FAPbI₃ (FA= formamidinium) faiblement confinées, et a permis de dissocier les processus de retardement de relaxation à haute puissance d’excitation dus aux effets de « hot phonon bottleneck » et de ré-excitation par recombinaison Auger (RA). Par ailleurs, l'analyse globale de l’évolution spectrale a été essentielle afin d’examiner les dynamiques de relaxation dans les NPLs 2D à fort confinement quantique et diélectrique, présentant des effets Stark importants et une transition de bord de bande excitonique discrète. Comme dans les systèmes faiblement confinés, le taux de relaxation dans les NPLs diminue avec la puissance d'excitation. Cependant, il est plus rapide dans les systèmes présentant un confinement plus important, mettant alors en évidence l'absence de ”phonon bottleneck” intrinsèque. La nature des cations internes (FA, MA=méthylammonium ou Cs) n’influe pas ce taux, ni son évolution en puissance. Toutefois, les mesures dans les films de pérovskite 2D présentant une épaisseur de puits quantique équivalente, suggèrent un rôle des ligands de surface dans la capacité à libérer l'excès d'énergie dans l'environnement. Ensuite, les recombinaisons multi-excitoniques dominées par la RA non radiative ont été étudiées dans les NPLs de pérovskite 2D fortement confinées. Dû à la géométrie asymétrique de ces nanostructures et de la délocalisation limitée de l'exciton, le temps de RA dépend fortement de la densité d'excitons via la distance inter-exciton moyenne : A faible puissance d’excitation, la RA est limitée par la diffusion de l'exciton dans le plan 2D et se produit sur plusieurs centaines de picosecondes (dépendant ainsi de la géométrie de l'échantillon). En revanche, une puissance d'excitation élevée produit des excitons dont les fonctions d’onde se recouvrent spatialement, entraînant des temps de RA inférieurs à 10 ps. Finalement, les dynamiques excitoniques dans les NPLs 2D ont été mesurées par AT après excitation dans l’ultraviolet afin d'observer le processus de multiplication d’excitons. Ce dernier implique la génération de plusieurs excitons “géminés”, et donc proches spatialement, suite à l'absorption d'un unique photon de haute énergieHalide perovskites have emerged as very promising photoactive materials due to their outstanding optoelectronic properties combined with low-cost processability. In spite of their successful implementation in photovoltaic or light-emitting devices, a deep understanding of the dynamics of relaxation and recombination is still missing in order to enhance the device performances. This thesis focuses on the study of two major fundamental processes occurring in colloidal halide perovskite nanostructures: the hot charge carrier/exciton relaxation (“cooling”), after excitation above the optical bandgap, and the non-radiative Auger recombination, taking place after high-fluence or high-photon energy excitation. In particular, time-resolved photoluminescence and femtosecond transient absorption spectroscopy were used to investigate the confinement and composition effects in strongly confined two-dimensional (2D) lead iodide perovskite nanoplatelets (NPLs), that were synthesized following the development and optimizations of colloidal methods. For the investigation of the cooling dynamics, a global analysis method based on single value decomposition was used, where the temporal evolution of the spectral lineshapes was modeled with a sequential kinetic scheme. This method was succesfully applied to effectively describe the continuous energy relaxation in weakly-confined thick FAPbI₃ nanoplates (FA=formamidinium) and allowed disantangleting the hot phonon bottleneck from the Auger reheating effects at high excitation fluence. Furthermore, the global analysis was essential to investigate the cooling dynamics in strongly confined 2D NPLs presenting large Stark effects and discrete excitonic band-edge transition far away from the continuum of states (exciton binding energy in several hundreds of meV). As in the weakly confined samples, the cooling rate of the NPLs decreases with the excitation fluence. However, it is faster in more-strongly confined samples, evidencing the absence of an intrinsic phonon bottleneck. Furthermore, the cooling rate and its evolution with the exciton density were found independent of the nature of the internal cations (FA, MA=methylammonium and Cs=cesium). However, when comparing with the rate measured in 2D layered perovskite thin film with equivalent quantum well thickness, the results strongly suggest a role of the surface ligands in the possibility to release the excess energy to the surrounding environment. This ligand-mediated relaxation mechanism becomes dominent in the thinner NPL samples with enhanced exciton/ligand vibrational mode coupling. Then, the multiple exciton recombination dominated by non-radiative Auger recombination (AR) was studied in the strongly-confined 2D perovskite NPLs. Due to the large asymmetric geometry and the limited exciton wavefunction delocalization, the AR rate strongly depends on the exciton density via the initial average inter-exciton distance. At low fluence, this distance is in several tens of nanometers such as the AR is limited by the exciton diffusion in the 2D plane. It thus occurs on a timescale of several hundreds of picoseconds and depends on the sample dimensionality (thickness and lateral sizes). In contrast, high excitation fluences produce “overlapping” excitons with inter-exciton distances of only a few times the exciton Bohr radius, resulting in AR times of less than 10 ps and independent of the NPL composition nor geometry. Finally, the exciton population dynamics of 2D NPLs after excitation in the ultraviolet was measured. The strong dependence of the AR with the inter-exciton distance allows the identification of multiple exciton generation (MEG), which involves the reaction of “geminate biexcitons” produced by the absorption of a single high-energy photon
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Stark, Thomas S. "Picosecond Dynamics of Free-Carrier Populations, Space-Charge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors." Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc2202/.
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Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power.Compound semiconductors are important photorefractive materials because they offer a near-infrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuous-wave, nanosecond- and picosecond-pulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications.In this dissertation, for the first time, we time-resolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semi-insulating GaAs and undoped CdTe. While CdTe offers a lattice-match to the infrared material HgxCd1-xTe, semi-insulating GaAs has been widely used in optoelectronic and high-speed electronic applications. We use a novel transient-grating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hot-carrier transport and the Dember space-charge field, and a long-lived nonlinearity that is due to the EL2 midgap species in GaAs. We numerically model our experimental results using a general set of equations that describe nonlinear diffraction and carrier transport, and obtain excellent agreement with the experimental results in both materials, for a wide variety of experimental conditions.
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Piccioni, Alberto <1993>. "Studies of the charge carrier dynamics and photoelectrocatalytic properties of V-modified TiO2 thin films." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9729/1/Piccioni_Alberto_tesi.pdf.
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This thesis aims to study the modifications induced by vanadium in titanium dioxide, an oxide semiconductor used for photoelectrocatalytic applications, such as water-splitting for hydrogen production and air and water remediation. The modification of this material is necessary to improve its conversion efficiency of light into chemical energy. In fact, its main limitation is the poor visible light absorption due to its wide energy gap (3.2 eV). In this work, V was introduced during the preparation of the sample, either in form of thin films or nanoparticles, using radio-frequency magnetron sputtering and inert gas phase condensation technique, respectively. A structural characterization by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that V does not induce critical changes in TiO2 matrix; X-ray near edge absorption spectroscopy was used to determine the local environment of V and Ti, revealing that V is substitutional. Femtosecond transient absorbance spectroscopy was adopted to provide the basis for the interpretation of the photoelctrocatalytic behavior of V-modified and unmodified TiO2, used as photoanodes in a photoelectrochemical cell. FTAS revealed that vanadium accelerates electron-hole recombination upon UV irradiation, explaining the lower conversion efficiency in the UV spectral range with respect to unmodified TiO2. In the visible range, for modified samples, FTAS revealed the presence of a transient signal due to free electrons and trapped holes after pumping at 530 nm. These results were supported by the new photoelectrocatalytic activity in the visible range, attributed to a V-induced introduction of intragap levels at ≈ 2.2 eV below the conduction band. Similar results were obtained for thin films and nanoparticle based samples. IPCE spectra showed that incorporation of vanadium in TiO2 extends water splitting in the visible range up to ≈ 530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range.
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Rueda, Delgado Diana Paola [Verfasser], and U. [Akademischer Betreuer] Lemmer. "Charge carrier dynamics and interfaces in perovskite solar cells / Diana Paola Rueda Delgado ; Betreuer: U. Lemmer." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1197138927/34.
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Rehman, Waqaas. "Ultrafast spectroscopy of charge-carrier dynamics and stability in lead-halide perovskites for thin-film photovoltaics." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:9bded808-276d-4ca5-bac9-d66cd99b67f5.
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Hybrid metal halide perovskites have emerged as an important new class of materials for photovoltaics. For their integration in tandem solar cells, optimised photocurrent matching between top and bottom cells requires careful control over bandgap energy and charge transport properties, for which tunable mixed bromide-iodide lead perovskites are the most prominent contenders. This thesis investigates photophysical properties of highly tunable mixed-halide and mixed-cation perovskite films with the aim of correlating their optoelectronic parameters with crystal phase changes induced by compositional variations. Firstly, the compositional variation of mixed-halide FAPb(BrxI(1-x))3 perovskites is explored. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the bromide content, x, suggesting a link with electronic structure. With rising x, the constants increase by up to an order of magnitude, yet still remain significantly below the Langevin limit. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm2 V-1 s-1 and diffusion lengths exceeding 1 μm, while mobilities across the mixed bromide-iodide system depend on crystalline phase disorder. Particularly, the mid-bandgap and bromide rich regions are found to be disordered and prone to photo-induced halide segregation. Subsequently, a highly crystalline mid-bandgap mixed-cation lead mixed-halide FA0.83Cs0.17Pb(Br0.4I0.6)3 perovskite is developed and investigated with focus on understanding the impact of adding caesium to the A-cation site in the lattice. Compared to single-cation FAPb(Br0.4I0.6)3, the crystal phase is stable and the chargecarrier mobility measured from THz spectroscopy reaches 21 cm2 V-1 s-1 resulting in a diffusion length of 3 μm. With photoinduced halide segregation being inherently suppressed, another benefit of controlled A-cation mixing could be revealed. In an aging-study, the correlation between the colloids concentration present in the precursor solution of FA0.83Cs0.17Pb(I0.8Br0.2)3 and nucleation stages for the crystallization of perovskite is explored. Having direct impact on morphology and photophysical properties, charge-carrier mobilities are reported to correlate with colloid concentration reaching > 20 cm2 V-1 s-1 for an optimum concentration. Ultimately, the full parameter space of mixed-cation (0 < y < 1) lead mixedhalide (0 < x < 1) CsyFA(1-y)Pb(BrxI(1-x))3 perovskites is examined, where crucial links between crystal phase stability, photo-stability and optoelectronic properties are highlighted. Finely tuning the caesium cation in the lattice yields excellent structural stability and charge-carrier transport properties for the parameter space between 0.1 < y < 0.3. For an optimized caesium content, the orthogonal halide-variation parameter space for Cs0.17FA0.83Pb(BrxI(1-x))3 achieves charge-carrier mobilities of 11 -40 cm2 V-1 s-1 and diffusion lengths of 0.8-4.4 μm.
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Husek, Jakub. "Elucidating Surface Charge Carrier Dynamics of Functional Materials By Femtosecond Transient Extreme Ultraviolet Reflection-Absorption Spectroscopy." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553099994360381.
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Yong, Chaw Keong. "Ultrafast carrier dynamics in organic-inorganic semiconductor nanostructures." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:b2efdc6a-1531-4d3f-8af1-e3094747434c.
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This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.
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Kilina, Svetlana V. "Phonon-assisted charge carrier dynamics and photoexcited state phenomena in nanoscale systems : semiconductor quantum dots and carbon nanotubes /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8593.
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Webb, Lauren J. Gray Harry B. "Chemical characterization and charge carrier dynamics of crystalline silicon(111) surfaces modified with surface-bound organic functional groups /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05262005-123044.
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Kiermasch, David [Verfasser], Vladimir [Gutachter] Dyakonov, and Christian [Gutachter] Schneider. "Charge Carrier Recombination Dynamics in Hybrid Metal Halide Perovskite Solar Cells / David Kiermasch ; Gutachter: Vladimir Dyakonov, Christian Schneider." Würzburg : Universität Würzburg, 2020. http://d-nb.info/1214594123/34.
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Hérissan, Alexandre. "Étude par Time Resolved Microwave Conductivity de photocatalyseurs pour la dépollution de l’eau." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS097/document.
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La photocatalyse se base sur l’excitation d’un semi-conducteur par des photons d’énergie supérieure ou égale à son gap, générant des paires électron-trous. Celles-ci sont très réactives et susceptibles de réagir à l’interface pour réaliser par exemple l’oxydation totale d’un composé organique. Cette méthode peut être appliquée sur des eaux usées pour éliminer totalement les polluants organiques qui y sont présents. Dans la perspective d’une utilisation du soleil comme source de lumière, cette méthode peut s’avérer très économique et écologique pour le traitement de l’eau.L’interaction lumière-semi-conducteur et la dynamique des porteurs de charge sont des processus physico-chimiques primordiaux pour la photocatalyse, et il est nécessaire de bien les comprendre pour maîtriser le procédé et développer des matériaux plus efficaces. La Time Resolved Microwave Conductivity (TRMC) est une technique qui se base sur la réflexion des micro-ondes sur un semi-conducteur excité qui est directement reliée avec le nombre de porteurs de charge photo-générés. Il s’agit d’un moyen de sonder en temps réel la dynamique des porteurs de charge dans les semi-conducteurs.Ce travail s’inscrit dans le cadre du projet ANR PhotoNorm. Il consiste en une étude par TRMC de dioxyde de titane TiO2 utilisé pour la dépollution de l’eau par photocatalyse. Une partie de cette étude concerne la caractérisation des propriétés opto-électroniques des matériaux, pour lesquels la dynamique des porteurs de charge sera comparée à l’activité photocatalytique. L’effet bénéfique en photocatalyse de la déposition de nanoparticules d'or, d'argent ou bimetallique or-cuivre sur des TiO2 commerciaux sera relié à une capture d’électrons libres observée en TRMC. L’effet bénéfique sur la photocatalyse en lumière visible a été relié à une injection d’électrons dans le TiO2 par des nanoparticules de bismuth. L’autre partie de ce travail consiste en une étude plus fondamentale de la dynamique des porteurs de charge dans des TiO2 commerciaux ou synthétisés dans le cadre du projet PhotoNorm. Il y sera montré l’importance de la longueur d’onde et de l’intensité d’excitation du matériau sur le rendement de génération de porteurs de charge. L’importance des effets de surface et de l’environnement seront aussi mis en évidence de plusieurs façons. La première consiste simplement en un traitement chimique de la surface (lavage), qui peut avoir une grande influence à la fois sur la dynamique des porteurs de charge et sur la photocatalyse, sûrement en lien avec la présence d’impuretés de surface. La seconde consiste à imprégner le TiO2 par des colorants organiques présentant une forte absorption en lumière visible. Les mesures de TRMC sur ces systèmes permettent de mettre en évidence l’interaction entre le semi-conducteur et les molécules extérieures adsorbées à sa surface, notamment l’injection d’électrons du colorant excité vers le semi-conducteur, mais aussi des effets de recombinaison accrus. La troisième méthode consiste à modifier l’atmosphère de travail en TRMC. Il y est observé notamment l’importance de l’oxygène sur la dynamique des porteurs de charge, et notamment les effets de captures d’électrons, phénomènes qui entrent en jeu dans le processus de photocatalyse.Au final, la TRMC s’avère être un bon moyen d’étude de la durée de vie des porteurs de charge dans les semi-conducteurs, qui peut permettre de mieux comprendre les processus fondamentaux associés à la photocatalyseThe photocatalysis is based on the excitation of semiconductor by photons with an energy superior or equal to the gap, generating electron-hole pairs. These are very reactive and able to react at the interface, involving for exemple the total oxidation of an organic compound. This method can be used on wastewater to eliminate the organic pollutants. With a view to use the sun as a light source this method may become an economical and ecological way for the water treatment. Light interaction between light and semiconductor and the charge-carrier dynamics are fundamental processes for photocatalysis and it is necessary to understand them in order to manage with this process and develop more efficient materials. The Time Resolved Microwave Conductivity (TRMC) is a method based on the reflexion of microwaves on an excited semiconductor which is linked to the number of photo-generated charge-carriers. This method allows us to probe in real time the charge-carrier dynamics in semiconductor. This work is included in the ANR Photonorm project. It consists in a TRMC study on titanium dioxyde TiO2 used for water depollution by photocatalysis. One part of this study consists in the characterization of the opto-electronic properties of materials for which the charge-carrier dynamics will be compared with the photocatalytic activity. The beneficial effect of nanoparticles deposition of gold, silver or gold-copper bimetallics on commercial TiO2 will be linked to the observation of free electrons observed by TRMC . The beneficial effect on photocatalysis in visible light was linked to an electron injection in TiO2 by bismuth nanoparticles. The second part of this work consists in a more fundamental study of charge-carrier dynamics on commercial or synthetized for the Photonorm project. I will be shown the importance of excitation wavelength and intensities on charge carrier generation. The importance of surface effect and environment will be emphasized by several ways. The first one just consist in surface treatment which can have a major importance on charge-carrier dynamics and photocatalysis, probably in connection with the presence or not of impurities on the surface. The second way consists in impregnating TiO2 by organic dyes which show a strong visible light absorption. The TRMC measurements highlight the interaction between the adsorbed molecules and the semiconducteur, including the electron injection from the excited dye to the TiO2 but also an increased recombination effect. The third method consist in modified the working atmosphere in TRMC. The major role of oxygen is so observed on charge-carrier dynamics, with an effect of electron capture, involving in photocatalytic mechanism.Finally TRMC proves to be a convenient method for studying charge-carrier dynamics in semiconductors, which allow a better understanding of fundamental processes bound to photocatalysis
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Lohrenz, Jan [Verfasser], Markus [Akademischer Betreuer] Betz, and Torsten [Gutachter] Meier. "Aspects of charge carrier dynamics in Germanium and cadmium zinc telluride / Jan Lohrenz ; Gutachter: Torsten Meier ; Betreuer: Markus Betz." Dortmund : Universitätsbibliothek Dortmund, 2016. http://d-nb.info/1121303005/34.
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Peckus, Domantas. "Ultrasparti eksitonų ir krūvininkų dinamika nanostruktūrizuotuose molekulių sluoksniuose." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20131220_150507-86088.
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Dėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių.
Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai.
PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui.
Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose.
Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą]Due to their unique properties organic semiconductors may be used for various applications in organic optoelectronic devices: light emitting devices, lasers, field-effect transistors and photovoltaic cells and etc. Despite high perspectives of organic semiconductors they are still upstaged by their inorganic counterpart. The efficiency of electrooptical properties of organic semiconductors is tried to increase. The main goal of this thesis is a detailed investigation of ultrafast exciton and charge carrier processes in pure organic semiconductors and their blends with fullerene derivatives. Measured organic or silicon organic semiconductors were poly-di-n-hexylsilane (PDHS), polyfluorenes F8BT and PSF-BT, merocyanine MD376. Fullerenes used in blends were C60 and its derivative PCBM. Ultrafast transient absorption, fluorescence, and integral mode photocurrent measurements were used for investigations. The investigation of PDHS revealed that PDHS nanocomposites can be used for improvement of neat PDHS films fluorescence properties. The formation of intramolecular charge transfer state was proposed for PSF-BT neat films. Charge transfer scheme of the formation of long-lived charge pair state in PSF-BT/PCBM blend was presented. The formation of charge transfer states was explored in neat merocyanine films and blends with fullerene derivatives. The scheme of generation of charge pairs and free charge carriers in merocyanine blends with fullerene derivatives was discussed in... [to full text]
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Green, Travis Christopher. "Photo-induced charge carrier dynamics and self-organization in semiconductor and metallic nanocrystals : in between the bulk and individual molecules." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30480.
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Handloser, Karl Matthias [Verfasser], and Achim [Akademischer Betreuer] Hartschuh. "Optical investigation of charge carrier dynamics in organic semiconductors and graphene for photovoltaic applications / Karl Matthias Handloser. Betreuer: Achim Hartschuh." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/1050648013/34.
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Chavez, Cervantes Mariana [Verfasser], and Isabella [Akademischer Betreuer] Gierz. "Photo-Carrier Dynamics and Photo-Induced Melting of Charge Density Waves in Indium Wires / Mariana Chavez Cervantes ; Betreuer: Isabella Gierz." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1212585143/34.
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Mori, Daisuke. "Development of Polymer Blend Solar Cells Composed of Conjugated Donor and Acceptor Polymers." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199331.
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森, 大輔. "電子ドナーおよびアクセプター性共役高分子からなる高分子ブレンド薄膜太陽電池の開発." Kyoto University, 2015. http://hdl.handle.net/2433/199528.
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