Photovoltaic (PV) cells with a three dimensional (3D) morphology are an exciting new research thrust with promise to create cheaper, more efficient solar cells by allowing for a "bottom up" approach to texturing thin film solar cells. This work introduces a new type of 3D PV device based on carbon nanotube (CNT) arrays. These arrays are paired with the thin film heterojunction, CdTe/CdS, to form a complete 3D carbon nanotube PV device (3DCNTPV). A complete theory for the power increase at off-normal angles of solar flux is developed for these cells. Marriage of a complicated 3D structure with production methods traditionally used for planar CdTe solar cell is challenging. This work examines the problems associated with processing these types of cells and systematically alters production methods of the semiconductor layers and electrodes to increase the short circuit current, eliminate parasitic shunts, and increase the open circuit voltage.

Organische Solarzellen besitzen das Potential für leichte und zugleich flexible photovoltaische Anwendungen, die kostengünstig hergestellt werden können und damit einen Beitrag zur Verminderung der Emission von Kohlendioxid, Methan und Stickoxiden leisten können. Zur Herstellung von organischen Solarzellen werden nur geringe Mengen der organischen Materialien benötigt und die Prozessierung findet bei vergleichsweise geringen Temperaturen statt, was die Abscheidung auf z. B. Plastikfolie ermöglicht. Man unterscheidet drei Arten von organischen Solarzellen. Erstens, Solarzellen bestehend aus kleinen Molekülen, die im Vakuum durch Sublimation auf das Substrat abgeschieden werden. Zweitens, Polymersolarzellen, deren Schichten aus Lösung meist durch „spin-coating“ oder Druckverfahren präpariert werden. Und drittens, „dye-sensitized“ Solarzellen (auch Grätzel-Zellen), die aus einer porösen Schicht Titandioxid und einem flüssigen Elektrolyten für den Ladungsträgertransport bestehen. Diese Arbeit beschäftigt sich ausschließlich mit organischen Solarzellen aus kleinen Molekülen. Die höchsten erreichten Wirkungsgrade organischer Solarzellen aus kleinen Molekülen liegen derzeit bei etwa 5 % . Um die Effizienzen von Solarzellen aus kleinen Molekülen zu steigern, ist es einerseits notwendig das Verständnis der physikalischen und chemischen Prozesse innerhalb der Bauelemente genauer beschreiben zu können, andererseits werden neue Materialien mit optimierten Eigenschaften für die organische Photovoltaik benötigt. In dieser Arbeit wurden zwei Strategien zur Optimierung organischer Solarzellen verfolgt: • Durch die Optimierung des Versatzes der Energieniveaus der organischen Materialien konnte die Leerlaufspannung in einem Modellsystem maximiert werden. An diesem Modellsystem wurden der Ursprung der Leerlaufspannung und die Rekombinationsdynamik von photogenerierten Ladungsträgern untersucht. Bezüglich der Leerlaufspannung zeigen Solarzellen, deren photoaktive Materialien in einer Mischschicht vorliegen, im Vergleich zu Solarzellen, die eine photoaktive Doppelschicht beinhalten, fundamentale Unterschiede . • Des Weiteren wurden neue Thiophenderivate untersucht, die als aktive Materialien in organischen Solarzellen eingesetzt wurden. Durch elektronenziehende Endgruppen wurde das Ionisationspotential der Thiophenderivate abgesenkt und die optische Bandlücke verringert. Das Thiophenderivat DCV3T fungiert in Kombination mit herkömmlichen Donator-Materialien als Akzeptor. In Mischschichten aus DCV3T und C60 kommt es durch einen Hin- und Rücktransfer der Anregungsenergie zwischen den Materialien statt der Generation von freien Ladungsträgern zu einer Erhöhung der Triplett-Exzitonendichte auf DCV3T . Diese Exzitonen besitzen auf Grund der hohen Lebensdauer von Triplett-Exzitonen das Potential für eine erhöhte Exzitonendiffusionslänge, die in einem neuen Solarzellenkonzept ausgenutzt werden konnte . / Organic solar cells have the potential for light weight and flexible applications. They can be manufactured cost-effectively and can thus contribute to the reduction of the emission of carbon dioxide, methane and nitric oxides. In order to manufacture organic solar cells, only small amounts of organic materials are required. They can be processed at comparably low temperatures. Therefore, the fabrication on substrates like plastic foil is possible. Three different types of organic solar cells exist. The first kinds are solar cells prepared from small molecules that are manufactured via sublimation of the material in a vacuum. The second kind are polymer solar cells manufactured from solution by spin coating techniques or ink jet printing. And thirdly, dye sensitized solar cells - also known as Grätzel cells - consisting of a porous layer of titanium dioxide and most commonly a liquid electrolyte for the charge transport. This work deals exclusively with small molecule solar cells. The highest power conversion efficiencies reached by small molecule organic photovoltaics are now in the range of 5 %. In order to increase the efficiencies of solar cells prepared from small molecules, two major aspects must be developed. The understanding of the physical processes within the organic devices must be improved. And secondly, new materials are required with physical properties optimized for organic photovoltaics. In this work, I followed two strategies for optimizing organic solar cells: • By optimizing the offset of energy levels between donor and acceptor material, the open circuit voltage could be increased. In the investigated model system, the origin of the open circuit voltage and the recombination dynamics of photo generated charge carriers were analyzed. Concerning the open circuit voltage, solar cells consisting of a donor acceptor double layer structure, show fundamental differences to solar cells consisting of a donor acceptor blend. • Furthermore, new thiophene derivatives used as photoactive materials were investigated. By the attachment of electron withdrawing end groups, the ionization potential of the oligothiophenes is increased and the optical band gap is reduced at the same time. The investigated thiophene derivative DCV3T acts as an acceptor in combination with the commonly used donor-materials. A back- and forth-transfer of excitation energy is observed in blends of DCV3T and fullerene C60. In these blends, excitons are not separated into free charge carriers. This back and forth transfer leads to an enhancement of the density of triplet excitons on DCV3T. These excitons have a potentially high diffusion length due to the long lifetime of triplet excitons. This effect was utilized in the organic solar cells.

<p>Organic solar cells have caught considerable attention in the past few years due to their potential for providing environmentally safe, flexible, lightweight, inexpensive, and roll-to-roll feasible production solar cells. However, the efficiency achieved in current organic solar cells is quite low, yet quick and successive improvements render it as a promising alternative. A hopeful approach to improve the efficiency is by exploiting the tandem concept which consists of stacking two or more organic solar cells in series.</p><p>One important constituent in tandem solar cells is the middle electrode layer which is transparent and functions as a cathode for the first cell and an anode for the second cell. Most studies done so far have employed noble metals such as gold or silver as the middle electrode layer; however, they suffered from several shortcomings especially with respect to reproducibility.</p><p>This thesis focuses on studying a new trend which employs an oxide material based on nano-particles as a transparent cathode (such as Zinc-oxide-nano-particles) along with a transparent anode so as to replace the middle electrode.</p><p>Thus, this work presents a study on solution processable zinc oxide (ZnO) nanostructures, their proper handling techniques, and their potential as a middle electrode material in Tandem solar cells in many different configurations involving both polymer and small molecule materials. Moreover, the ZnO-np potential as a candidate for acceptor material is also investigated.</p>

Title from PDF of title page. / Document formatted into pages; contains 78 pages. / Thesis (M.S.E.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: With CdTe based photovoltaics developed by close spaced sublimation reaching efficiencies of over 16%, commercialization of this technology draws serious attention. Today large area industrial modules have not been able to produce the same performance of their laboratory counterparts. This work provides a means for understanding the various technical challenges in developing an effective deposition technology for large area processing. The submodule process investigated provides a model for continuous and sequential processing of subsequent films. The system has a unique design and constructed with the provision for a moving transport module for the substrate transport. The process was developed to deposit large area CdTe (3 x 3 sq. inch) and provides valuable insights for the development of a large area deposition system. Upon optimizing the system for reproducibility, proper deposition conditions were established. / ABSTRACT: Films deposited under various conditions were studied to improve our understanding of the influence of processing conditions on device performance. The key advantage of this technique over others is its high deposition rate, simplicity of operation and high conversion efficiency. Typical deposition times were two minutes and could be reduced to as low as 45 sec with little variation in performance. The four major parameters that influence the films prepared by close spaced sublimation, namely substrate temperature, source temperature, ambient pressure, and spacing were optimized for best device performance. The influence of each parameter on deposition rate and cell efficiency was also studied. The best cells produced by this technology had an efficiency of 13% with Voc=830 mV, FF= 74% and Jsc=21.1 mA/cm2. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Parts of the auxiliary power systems at Fortum's hydro power stations are usingdirect current, which is fed from the generators at the plant and converted byrectifiers. As photovoltaic solar cells produce direct current there are severalhypothetical advantages to use solar power for the auxiliary power supply, e.g.enabling more of the power from the generator to be sold to the grid. It eliminatesthe need of an inverter, conversion losses are avoided and less load is put on therectifiers. However the exclusion of an inverter also prevents the solar cells to have adirect connection to the grid, which in turn makes them ineligible for the Swedishgovernmental solar power investment support program. The lesser load on therectifiers will not affect their lifetime according to manufacturers and thus achieves noeconomic gain. Avoiding conversion losses will increase the gain from the producedelectricity by enabling even more power to be sold to the grid. The economic gainfrom avoiding conversion losses is however too small to gain any feasibility in a smallsolar power installation at a hydro power plant, as the small size will make itexpensive in terms of investment per Wp.

Syftet med rapporten är att beskriva hur fastighetsbolaget, Varbergs Fastighets AB och energibolaget, Halmstad Energi och Miljö hanterar de risk-, och osäkerhetsfaktorer som förekommer vid solcellsinvesteringar. För att energisamhället skall nå en hållbar framtid krävs att elproduktionen kommer ifrån förnybara energikällor. Sedan år 2008 har installationstakten för solceller i Sverige ökat. År 2012 installerades 8,3 MW solceller och år 2013 mer än fördubblades den installerade effekten till 19 MW (Lindahl, 2014). Trots utvecklingen står solenergin för 0,03 procent av Sveriges totala elproduktion, vilket kan jämföras med Tyskland där solenergin står för 5,3 procent av den totala elproduktionen år 2014 (IEA International energy agency, 2014). En investerare vill från investeringen nå en så hög avkastning som möjligt och samtidigt reducera och undvika de uppkomma riskerna. Det multinationella brittiskt-amerikanska revisor och konsultföretaget Pricewaterhousecoopers definierar risk som en osäker framtida händelse som kan påverka företagets möjlighet att uppnå de framtida strategiska, operationella och finansiella mål (Pricewaterhousecoopers, 1999). Den här studien har sin utgångspunkt i den samhällsvetenskapliga hermeneutiken. Studien antar att verkligheten är subjektiv och att observationer av den kräver tolkning. Det resultat som presenteras kommer därmed vara en tolkning av verkligheten och inte resultera i några generella teorier (Eriksson &amp; Wiedersheim-Paul, 2014). Vår kvalitativa fallstudie grundar sig i en induktiv ansats där vi samlat in empirisk data genom att intervjua två företag och en solcellsexpert. Vi har intervjuat Varbergs Fastighets ABs processledare och hållbarhetsansvarig och Halmstad Energi och Miljös strategichef. Vi har även intervjuat branschorganisationen Svensk solenergis ordförande. Våra respondenter har stärkt vårt arbete med konstruktiv data för att vidare studera risk och osäkerhet i solcellsinvesteringar. Studien tyder på att de risker som föreligger vid solcellsinvesteringar är förhållandevis lika mellan aktörerna men det som skiljer är företagens riskhanteringsstrategier för att behandla dem. De allmänna riskerna som belyses av solcellsexperten är i enlighet med de risker som företagen påvisar men att den genomgående risken är en allmän låg kunskap kring solceller. / This study attempts to describe how the real estate company, Varbergs Fastighets AB and the energy-company, Halmstad Energi och Miljö copes with factors of risks and uncertainties that may occur while investing in photovoltaic. To enable the energy society to attain a sustainable future, the production of energy must be provided by renewable sources. Since 2008, the rate of the installation of photovoltaic in Sweden has increased. In 2012, 8.3 MW of solar cells were installed and by 2013, the installed effect was more than doubled (Lindahl, 2014). Despite this bright development, the solar energy in Sweden only provides 0.03 percent of the overall energy production in the year of 2014 (IEA International energy agency, 2014). An investor wants from the investment reach as high a return as possible while reducing and avoiding the risks incurred. The multinational British-American accountant and consulting firm PricewaterhouseCoopers defines risk as an uncertain future event that may affect the company's ability to achieve future strategic, operational and financial targets (PricewaterhouseCoopers, 1999). This study takes its point of departure in the hermeneutics of the social science. The study assumes that the reality is subjective, and thus demands an interpretation of the observations from it. The result presented in this report will therefore be an interpretation of the reality and consequently not answer in any general theories (Eriksson &amp; Wiedersheim-Paul, 2014). Our qualitative case study has its base in an inductive approach, where empirical data has been gathered by interviewing two companies and one expert of photovoltaic. We have interviewed the process manager and the manager of sustainability of Varbergs Fastighet AB and the strategy executive of Halmstad Energy och Miljö. We have also interviewed the chairman of Swedish solar energy. Our respondents have strengthened our work with constructive data, to further study the risks and uncertainties associated with investments in photovoltaic. This study indicates that the risks presented by investments in photovoltaic are relatively similar between the operators, but the distinguishing factor is the treatment of the risks by the companies. The common risks illuminated by the experts of photovoltaic runs accordingly with the risks demonstrated by the companies, though it is clear that the pervading risk is general poor knowledge of photovoltaic.

Thin film solar cells with Copper Indium Gallium Diselenide (Cu(In,Ga)Se2) absorber layers is one of the most promising candidates to emerge as an efficient solar cell technology in the near future. CIGS cells with efficiencies of 19.2 % have already been reported [1]. In this study, CIGS absorber layers are fabricated by a two-stage all-solid-state manufacture-friendly process. In the first stage, designated as precursor deposition, Copper and Gallium are sequentially deposited followed by co-deposition of Indium and Selenium. In the second stage, designated as selenization, the substrate is annealed at high temperatures in a selenium environment during which a thin layer of copper is also deposited. The typical thickness of the absorber layers fabricated by this process is around 2um. The ZnO transparent front contact of these cells is a bi-layer with a thin intrinsic layer and a thicker Al doped n-type layer. These layers have been fabricated by different methods using Al-doped and undoped ZnO targets. The effect of the intrinsic layer thickness on the device performance was studied. Best performances were obtained when the intrinsic layer was around 350° thick and fabricated from an Al-doped ZnO target with excess oxygen partial pressure during deposition. The main focus of this work is to reduce the thickness of the CIGS absorber layers with no or minor loss in efficiency as this would translate directly into reduction in production costs and the amount of material being used. Reducing the thickness can be done either by reducing the deposition rates or duration of deposition. Due to the complex time-temperature profile during fabrication, reducing the thickness by reducing the deposition time would also affect the duration for which the substrates will be at high temperatures. To understand what effect this would have in film formation and performance of the device, and if any post-deposition annealing would be required to compensate for the reduced time at temperatures, experiments were carried out with the cells being annealed at different stages before and after completion of the device itself. Annealing was done at 250°C in both air and vacuum. Although annealing the finished devices always yielded poorer performance, it was certainly helpful in understanding which aspects of the device were affected. Devices with reduced absorber layer thicknesses of 1.5um, 1.0um and 0.65um were fabricated. The devices showed improved Voc's when the absorber layer thickness was reduced to 1.5um and 1.0um but the Jsc's dropped by 2-3 mA/cm2. The 1.0um thick devices also showed an increase in band gap. The thickness of the Molybdenum back contact layer was increased to see if the amount of Sodium from the substrate had any effect on the device performance. The Ga/In ratio was altered and its effect was also studied. The 0.65um thick devices showed a large reduction in Voc's and Jsc's. The effect of Selenization time and Selenium flux during Selenization were studied at each of the different thicknesses.

Cadmium Telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal bandgap of 1.45 eV and its high optical absorption coefficient. The typical CdTe thin film solar cell is of the superstrate configuration where a window layer (CdS), the absorber (CdTe) and a back contact are deposited onto glass coated with a transparent electrode. Substrate CdTe solar cells where the above listed films are deposited in reverse are not common. In this study substrate CdTe solar cells are fabricated on flexible foils. The properties of the Molybdenum back contact, Zinc Telluride (ZnTe) interlayer and CdTe absorber on the flexible foils were studied and characterized using X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Substrate curvature and film flaking was observed during the fabrication as a result of differences in thermal expansion coefficients between the substrate and the deposited films, and also due to impurity diffusion from the foil into the film stack. In order to overcome this problem diffusion barriers where used to eliminate contamination. Silicon dioxide (SiO2), silicon nitride (Si3N4) and molybdenum nitride (MoxNy) were used as such barriers. Electrical characterization of completed devices was carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V) and Spectral Response (SR) measurements. Roll-over was observed in the first quadrant of J-V curves indicating the existence of a back barrier due to a Schottky back contact. The formation of non-rectifying contact to p-CdTe thin-film is one of the major and critical challenges associated with the fabrication of efficient and stable solar cells. Several materials (ZnTe, Cu, Cu2Te, and Te) were studied as potential candidates for the formation of an effective back contact.

A survey of residential solar photovoltaic (PV) adopters in Texas was administered and the results are presented and discussed. A 40% response rate was achieved and 365 complete responses were received. In addition to demographics, the survey uncovered aspects related to the decision-making process, information search, financial attractiveness of PV, and post-installation experience. Peer-effects did not have a large influence on the adoption of residential PV in Texas, but the potential for increasing the number of communication/information channels to increase the adoption rate of PV exists. Adopters experienced little uncertainty at the time of PV installation because sufficient dependable information was available during the search process. Overall, they are satisfied with PV. Contextual factors, such as income and the ability to purchase a PV system rather than lease one, influence behavior. Those who decreased electricity consumption post-adoption were more motivated to adopt by environmental concern and a general interest in energy than those who increased electricity consumption post-adoption. Those who experienced behavior changes also experienced an increase in awareness of electricity use post-adoption, while those who did not experience a behavior change reported no change in awareness post-adoption. Change in awareness of electricity use is less dependent on the attitudinal and contextual factors, such as environmental concern, motivation for adoption, age, and income, that influence consumption change. The potential for further analysis of the survey results is great and will likely yield additional conclusions about the consequences of the adoption of PV. Coupling the survey results with historical electricity bill data will yield stronger conclusions about behavior change. Surveying geographical areas outside of Texas is recommended. / text

Described herein are two projects focusing on developing and investigating two types of nanoparticles (NPs) grown by the seeded growth method from a conducting metallopolymer for photovoltaic (PV) applications. Core/shell CdS/ZnS NPs are proven to resist the photo-oxidation of PV devices, while CuInxGa(1-x)Se2 (CIGS) NPs are expected to optimize the efficiency of PV devices. / text