Thesis (M.S.)--Missouri University of Science and Technology, 2010. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed July 19, 2010) Includes bibliographical references (p. 88-90).

Thesis (Dipl.-Ing.)--Johannes Kepler Universität Linz, 2005. / Title from PDF title page (viewed Apr. 29, 2010). Abstract also in German. Includes bibliographical references (p. 60-63).

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Idaho, 2005. / Also available online in PDF format. Abstract. "July 2005." Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 109-126).

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

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Over the last 4 years, perovskite solar cells emerged as an attractive, highly efficient, and low-cost alternative to established, conventional photovoltaic technologies. The power conversion efficiency of these devices recorded an unprecedented rise, currently exceeding certified values of 20%. This thesis covers a number of technological advancements which lead to improved photovoltaic performance, as well as vital insight into some more fundamental aspects of the perovskite device operation. The focus of this body of work is primarily directed towards the electric contact in the PV stack which is responsible for electron collection. The motivation of the study presented here is given in Chapter 1, and includes a brief summary of the current energy landscape. Chapter 2 introduces the theoretical background of photovoltaic technology, starting from the basics of semiconductor physics, through to the principles of solar cell operation, as well as some characteristic properties of the perovskite materials. Details of the experimental methods used in this study are reported in Chapter 3. Chapter 4 reports the development of a low temperature process (sub-150 °C) for the manufacture of perovskite solar cells. Dispersions of pre-synthesised, highly crystalline TiO2 nanoparticles were used as an electron selective contact, which eliminated the high temperature sintering step. Chapters 5, 6 and 7, report the interface modification of an n-type contact, resulting in a substantially improved device operation and suppression of hysteresis phenomenon which is characteristic of perovskite photovoltaics. Fullerene-based materials have been found to make excellent electronic contact with halide perovskite materials, and are shown to be far superior to commonly used metal oxides. The facilitated electron collection allows enhancements in the photovoltaic performance of these devices. Furthermore, the organic layers used in this study can be processed at low temperatures. Finally, the development of transparent conductive electrodes based on silver nanowires is presented in Chapter 8. The fabricated electrodes exhibit low sheet resistance, high degree of transparency, and can be processed at low temperatures, allowing them to be compatible with processing on flexible substrates and multi-junction architectures. The application of silver nanowires in different perovskite solar cell architectures is also reported.

This thesis is an investigation of the photophysical processes that occur in organic photovoltaic blends in the time between light being absorbed and free charges being generated. The purpose of all solar cells is to generate a photocurrent. The free charges, as they flow out of the device, make up the photocurrent, so understanding the processes by which they are created is vitally important to organic photovoltaic research. The main experimental method used was time-resolved fluorescence spectroscopy. This technique was used to probe the exciton population with respect to time for a variety of blends of organic semiconductors, including the high performance photovoltaic materials PCDTBT, PTB7, C71-PCBM and P3HT. The main goal of the work was to characterise the exciton diffusion lengths of these materials by developing a technique called volume quenching. Volume quenching involves blending a small quantity of quenching material into a thin film of semiconducting material. These introduced quenching sites render excitons unemissive on contact. Thus, from the drop in fluorescence compared with the ‘unquenched' material, it was possible to work out what proportion of the initial excitons have encountered a quenching site in the blends. The results can then be fitted to quantify how diffusive the excitons are -i.e. how far they move. By looking at the rate constant of the quenching process and how it varies with respect to time, quencher concentration and quencher type, it was possible to generate a wealth of additional information, not just about exciton diffusion, but about all the inter-related processes that contribute to exciton harvesting. These processes included the measurement of long-range energy transfer from the donor to the acceptor, electron transfer at the interface with the acceptor and the understanding of nanomorphology of donor-acceptor heterojunctions.

L’oxyde de zinc est un semiconducteur pressenti pour une large variété d’applications optoélectroniques, biologiques ou encore détecteurs de gaz. En effet, en plus d’être un matériau abondant, il possède plusieurs propriétés remarquables comme sa large bande interdite de 3,33 eV, sa grande mobilité électronique de 200 cm²/(V.s) mais également sa capacité à croitre sous plusieurs formes nanométriques par des techniques de dépôt bas coût et facilement adaptables au milieu industriel. Les nanofils de ZnO élaborés par la technique de dépôt en bain chimique seront utilisés dans cette thèse pour leur intégration dans des cellules solaires de 3ème génération. Dans ces cellules, la morphologie des nanofils ainsi que leur dopage est primordial pour obtenir des rendements intéressants. Ce dernier aspect en particulier n’a cependant pas été étudié en détails dans la littérature concernant le dépôt en bain chimique. Ce travail présente donc une façon innovante de contrôler simultanément la morphologie et le dopage des nanofils par cette technique de dépôt. Un mécanisme de croissance et de dopage a été déterminé grâce à des simulations thermodynamiques, des mesures de pH in-situ et plusieurs méthodes de caractérisation telles que la microscopie électronique à balayage et à transmission, la diffraction des rayons X, la spectroscopie Raman en température et la microscopie à force atomique en mode électrique. Les nanofils de ZnO réalisés sont ensuite intégrés dans des cellules solaires à colorant pour étudier l’intérêt de l’optimisation des nanofils sur les performances des cellules solaires. Finalement, ces nanofils de ZnO combinés à une électrode en nanofils d’argent peuvent être intégrés sur substrat flexible pour réaliser une cellule à colorant plus légère et maniable et donc visant davantage d’applications. / Zinc oxide is a semiconductor considered for a wide range of optoelectronic, biological, or gas sensor applications. Indeed, apart from being an abundant material, it has several remarkable properties as its electronic mobility (200 cm²/(V.s)) and his ability to grow under different nano-scale shapes thanks to low cost and easily scalable deposition techniques. ZnO nanowires grown by the chemical bath deposition technique are used in this thesis for their integration in 3rd generation solar cells. In these devices as in many other applications, the nanowire mophology and electrical property are essential to get interesting efficiency. This last aspect, in particular, has never been studied in details in the literature concerning chemical bath deposition. This work introduces a new way to control simultaneously the morphology and the doping level of ZnO nanowires by this deposition technique. A growth and doping mechanism has been identified thanks to thermodynamics simulations, in-situ pH measurements, and several characterization techniques like scanning electron microscope, X-ray diffraction, temperature dependant Raman spectroscopy, and atomic force microscopy. The ZnO nanowires were also embedded in dye sensitized solar cells to study the effect of morphology and doping level on the efficiency. ZnO nanowires combined with an Ag nanowire electrode can be deposited on a flexible substrate to make a flexible dye sensitized solar cell.