This research describes an investigation on the fabrication of CuInSe2-based thin-film solar cells with the device structure of Al/ZnO:Al/ZnO/CdS/CIS/Mo/SLG at the substrate temperature of 450oC, which is at least 100oC below the temperature currently used for depositing CIS thin films. A great advantage for the low temperature process is that the polymer material can be used as substrate and it is feasible to make lightweight and flexible thin-film solar cells. In this work, we used a co-evaporation technique with an introduction of Sb during the film deposition process to modify the film growth mechanisms and produce the CIS film with compact grain structure and smooth surface morphology. In most cases, there was only tiny amount of Sb existed in the film as a p-type dopant. In some cases, second phases of Sb compounds could be detected in the film as the Sb flux was kept too high during the film deposition stage. The I-V characteristics measured under the AM1.5 condition for the solar cell using a CIS:Sb film as the absorber showed that the open circuit voltage (Voc) was 0.364 V, short circuit current (Jsc) was 48.16 mA/cm2, fill factor (FF) was 44.5%, and energy conversion efficiency (£b) was 8%. The device with the same layer structure except the use of CIS film prepared without the addition of Sb and at a higher substrate temperature of 550oC had a comparable device performance but a slightly lower efficiency, i.e. Voc=0.325 V, Jsc=48.54 mA/cm2, FF=45.1%, £b=7.4%. It is clear that a lower temperature process using Sb to modify the growth process can be successful to obtain a device quality CIS layer. In addition, a CIGS thin-film solar cell was also fabricated and its device properties were Voc=0.392 V, Jsc=37.28 mA/cm2, FF=46.2%, and £b=7.0%. We see that the addition of Ga to increase the bandgap do increase the Voc and decrease the Jsc. However, a low efficiency of this cell indicates that further improvement in fill factor of the cell is a necessary.

In this research, gel-state and quasi-solid state dye-sensitized solar cells (DSSCs) were fabricated with polydimethylbenzimidazole(PDMBI) as the polymer electrolyte. These devices are stable under room light in air, even without encapsulation. The energy conversion efficiency of gel-state cells was drastically increased around 200% after the device worked. We propose that appropriately aggregated PDMBI in electrolyte layer could provide pathways which would facilitate the diffusion of ion through the electrolyte. Moreover, this arrangement induces it an ion exchange reaction which could lead to the promotion of the diffusion rate between iodide species. An optimized device performs well with a power conversion efficiency of 4.98% under air-mass 1.5 global (AM 1.5G) illumination. For the fabrication of quasi-solid state dye-sensitized solar cells, we immersed a few liquid electrolyte to improve electrical contact between TiO2 porous layer and PDMBI layer. The quasi-solid state cell efficiency fabricated with PDMBI as electrolyte was 2.26%. Furthermore, our device architecture is performing well because of the good band alignment among TiO2, dye, and PDMBI. In this research, we have successfully demonstrated gel-state and quasi-solid state dye-sensitized solar cells comprising PDMBI as electrolyte.

Wide band gap metal oxides have recently become one of the most investigated materials in surface science. Among these metal oxides especially TiO2 attracts great interest, because of its wide range applications, low cost, biocompatibility and ease of analysis by all experimental techniques. The usage of TiO2 as a component in solar cell technology is one of the most investigated applications of TiO2 . The wide band gap of TiO2 renders it inecient for isolated use in solar cells. TiO2 surface are therefore coated with a dye in order to increase eciency. This type of solar cells are called dye sensitized solar cells . The eciency of dye sensitized solar cells is directly related with the absorbed light portion of the entire solar spectrum by the dye molecule. Inspite of the early dyes, recent dye molcules, which are called wider wavelength response dye molecules, can absorb a larger portion of entire solar spectrum. Thus, the eciency of dye sensitized solar cells is increased by a considerably amount. In this thesis the electronic structure of organic rings, which are the fundamental components of the dye molecules, adsorbed on anatase (001) surface is analyzed using density functionaltheory. The main goal is to obtain a trend in the electronic structure of the system as a function of increasing ring number. Electronic structure analysis is conducted through band structure and density of states calculations. Results are presented and discussed in the framework of dye sensitized solar cells theory.

Organic semi-conductors are of great interest since these compounds can be utilized as active layers in many device applications such as ECDs, LEDs and solar cells. Incorporating the benzotriazole units into the polymer backbone enhances the optical properties of donor units. Hexyl thiophene and pyrrole are commonly used as electron donor materials. Benzotriazole can be coupled to hexyl thiophene or pyrrole to yield materials which can be polymerized to give donor acceptor type polymers. These materials are promising components in fast switching polymeric electrochromic devices and highly efficient photovoltaic devices. During thesis studies,poly(2-dodecyl-4,7-bis(4-hexylthiophen-2-yl)-2H-benzo[d][1,2,3]triazole) (PHTBT) and poly(2-dodecyl-4,7-di(1H-pyrrol-2-yl)- 2H- benzo [d] [1,2,3] triazole) (PPyBT) will be synthesized via N-alkylation, bromination, stannylation and Stille coupling reactions. Electrochromic and photovoltaic properties of the polymers will be investigated in detail.

Silicon is the most important semiconducting material for optoelectronics owing to its suitable and tunable physical properties. Even though there are several alternatives, silicon based solar cells are still the most widely produced and commercially feasible system. Extensive efforts have been spent in order to increase the efficiency and decrease the cost of these systems. The studies that do not focus on replacement of the semiconducting material, mostly concentrate on the developments that could be brought by nanotechnological approaches. In this aspect, utilization of silicon nanowires has been predicted to improve the efficiency of the silicon based solar cell technology. Moreover, besides solar cells, silicon nanowires have been investigated for many other electronic systems such as thermoelectrics, light emitting diodes, biological/chemical sensors, photodetectors and lithium ion v batteries. Therefore, production of silicon nanowires through a cost-effective and well controlled method could make important contributions to many fields. In this thesis, electroless etching method, which is a novel and solution based method enabling vertically aligned silicon nanowire array fabrication over large areas, is investigated. A detailed parametric study resulting in a full control over the resultant nanowire morphology is provided. The parameters affecting the structure have been determined as etching time, solution temperature, solution concentration, pressure and starting wafer characteristics. The results show that electroless etching method could replace the conventional silicon nanowire fabrication methods. It was shown that specific nanowire lengths for any application, can be obtained simply by adjusting the parameters of electroless etching system. One of the most crucial features of vertically aligned silicon nanowire arrays is their remarkable antireflective properties. The optical reflectivity measurements showed that 42% reflectivity of pristine polished silicon wafer decreases down to 1% following fabrication of silicon nanowire arrays on their surface. This unique characteristic reveals that these nanowires could be used as antireflective surfaces in solar cells. Moreover, it was determined that p-n heterojunctions that are formed by silicon nanowires, namely radial heterojunctions, would yield higher efficiencies compared to planar heterojunctions because of the dramatic increase in the charge carrier collection efficiency and orthogonal photon absorption. On this subject, n-type silicon nanowire arrays were fabricated by electroless etching followed by drop casting Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) organic layer on these nanowires as the complementary layer, forming the radial heterojunction. The energy conversion efficiency of silicon nanowire / PEDOT: PSS device was found as 5.30%, while planar silicon / PEDOT: PSS control device displayed only 0.62% efficiency. Developments and optimizations in both the electroless etching method and solar cell models could lead to important developments in photovoltaic industry.

2-Dodecyl benzotriazole and 9,9-dioctylfluorene containing alternating copolymers poly((9,9-dioctylfluorene)-2,7-diyl-(2-dodecyl-benzo[1,2,3]triazole)) (P1), poly((9,9-dioc-tylfluorene)-2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl benzo[1,2,3]triazole)) (P2), poly((9,9 dioctylfluorene)-2,7-diyl-(4,7-bis(3-hexylthien-5-yl) 2-dodecyl-benzo[1,2,3]triazole)) (P3) were synthesized via Suzuki polycondensation. Synthesized monomers and copolymers were characterized by Nuclear Magnetic Resonance (1H-NMR, 13C-NMR). Optical and electronic properties of resulting alternating copolymers were investigated by means of Cyclic Voltammetry (CV), Ultraviolet&ndash / Visible Spectroscopy and spectroelectrochemistry. All three polymers showed both p and n doping behaviors and multicolored electrochromic states. In order to learn switchingtimes and percent transmittance changes kinetic studies were also performed. Thermal properties of the polymers were investigated via Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Due to the convenient HOMO and LUMO levels, band gaps, strong absorptions in the visible region and thermal stability, polymers were tested in Organic Solar Cell (OSC) device applications. The preliminary investigation indicated that polymers had promising power conversion efficiencies.

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.

<p>This project is an extension of a pre-existing simulation program (‘Simulation_2dioden’). This simulation program was first developed in Konarka Technologies. The main purpose of the project ‘Simulation_2dioden’ is to calibrate the values of different parameters like, Shunt resistance, Series resistance, Ideality factor, Diode current, epsilon, tau, contact probability, AbsCT, intensity, etc; This is one of the curve fitting procedure’s. This calibration is done by using different equations. Diode equation is one of the main equation’s used in calculating different currents and voltages, from the values generated by diode equation all the other parameters are calculated.</p><p>The reason for designing this simulation_2dioden is to calculate the values of different parameters of a device and the researcher would know which parameter effects more in the device efficiency, accordingly they change the composition of the materials used in the device to acquire a better efficiency. The platform used to design this project is ‘Microsoft Excel’, and the tool used to design the program is ‘Visual basics’. The program could be otherwise called as a ‘Virtual Solar cell’. The whole Virtual Solar cell is programmed in a single excel sheet.</p><p>An Automated working solution is suggested which could save a lot of time for the researchers, which is the main aim of this project. To calibrate the parameter values, one has to load the J-V characteristics and simulate the program by just clicking one button. And the parameters extracted by using this automated simulation are Parallel resistance, Series resistance, Diode ideality, Saturation current, Contact properties, and Charge carrier mobility.</p><p>Finally, a basic working solution has been initiated by automating the simulation program for calibrating the parameter values.</p>

Title from PDF of title page. / Document formatted into pages; contains 70 pages. / Thesis (M.S.E.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Currently thin film solar cells have efficiencies in the range of 16-18%. Higher efficiencies of 20% or more can be achieved by two junction solar cells in which two p-n junctions are connected in series one on top of the other in a tandem structure. The ideal bandgaps for optimum efficiency in a tandem structure are about 1eV for the top cell and 1.7 eV for the bottom cell. Copper Indium Gallium di-Selenide (CIGS) with a bandgap of 1 eV is a suitable candidate for the bottom cell and Cadmium Zinc Telluride (CZT) with a tunable bandgap of 1.44-2.26 eV is a suitable candidate for the top cell. This work involves characterization of cadmium zinc telluride films and solar cells prepared by close spaced sublimation. CZT is deposited by co-sublimation of CdTe and ZnTe. The process has been investigated on various wide bandgap semiconductor materials including cadmium sulphide, cadmium oxide and zinc selenide. / ABSTRACT: Different post deposition heat treatments were carried out to determine their effect on film and device properties. Characterization of the CZT devices was done using XRD, EDS, SIMS, J-V and spectral response measurements. CZT (Eg 1.7 eV) /CdS exhibited best performance when compared to the other window layers investigated. The best device exhibited Voc=640mV, FF=40% and Jsc=4.5 mA/cm2. The theoretical performance of CZT based solar cells were investigated using SCAPS. The effect of bulk and interface defects on the device parameters were studied. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Thesis (Ph.D.)--University of Central Florida, 2008. / Adviser: Neelkanth G. Dhere. On t.p. "x" and "y" are subscripts. Includes bibliographical references (p. 130-142).