This PDF file contains the front matter associated with SPIE Proceedings Volume 7045, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The long-term performance data of copper indium diselenide (CIS) and gallium-alloyed CIS (CIGS) photovoltaic (PV) modules are investigated to assess the reliability of this technology. We study and report on numerous PV modules acquired from two manufacturers (A and B), deployed at NREL's outdoor test facility (OTF) in various configurations in the field: some are free standing, loaded with a fixed resistance and periodically tested indoors at STC; other modules are connected to data acquisition systems with their performance continuously monitored. Performance is characterized using current-voltage (I-V) measurements obtained either at standard test conditions or under real-time monitoring conditions: the power parameters plus other factors relating to quality like diode quality factors or series resistance are analyzed for changes against time. Using standard diode analysis to determine the sources of degradation indicates that CIS modules can exhibit between moderate and negligible degradation, with the dominant loss mode being fill factor declines along with decreases in open-circuit voltage, for illumination intensities near 1-sun. At lower intensities, current losses can appear appreciable. The real-time performance data also indicate that fill factor loss is the primary degradation mode, generally as a result of increases in series resistance.

Recent investigations of rapid thermal processing (RTP) of thin films using an in-situ optical process control in conjunction with in-situ energy-dispersive X-ray diffraction (EDXRD) are presented. The growth of Cu(In,Ga)(S,Se)₂ layers by sulfurization or selenization of sputtered Cu-In-Ga precursor layers was realized by a heating ramp from room temperature to temperatures between 500 and 550°C during which elemental sulfur or elemental selenium was evaporated by radiative heating. White light scattered at the surface of the growing Cu(In,Ga)(S,Se)₂ layers was monitored by a CCD camera in order to record in-situ the changing optical properties of the films. EDXRD was used to monitor the evolving structural properties of the growing films simultaneously. During the sulfurization and selenization process the growing films pass through various phase transition which could be correlated with the white-light scattering Detailed analysis of the time evolution of both signals (EDXRD and WLS) allowed to determine specific signatures in the WLS signals indicating the influence of the process parameters on the growth process of Cu(In,Ga)(S,Se)₂.

We have deposited textured ZnO:Al films over large areas using a reactive-environment hollow cathode sputtering (RE-HCS) system developed in house, and have achieved excellent carrier mobilities (up to 49.5 cm²/Vs at a carrier concentration of 4.42 x 10²⁰/cm³). Both the electrical properties and optical properties (total transmission and haze) are superior to those exhibited by commercially available SnO₂:F. Using these textured ZnO:Al films, we have achieved an a-Si:H solar cell efficiency boost of 8% relative to commercial SnO₂:F superstrates which resulted from improvements in all three PV parameters, namely V_oc, J_sc, and FF. We have also determined the dependence of cell performance on the degree of haze in the ZnO:Al films. Electrical, physical, and optical properties of ZnO:Al and SnO₂:F, as determined by four-point probe, Hall effect, SEM, AFM, ICP, transmission (total and diffuse), and work function measurements are presented and correlated to the observed differences in a-Si solar cell performance. We have also developed a refractive index matching layer that, when inserted between the TCO and the a-Si:H layers, resulted in an increase in J_sc of 3%. Finally, we present some experiments on the effect of TCO type on nc-Si:H solar cell performance. From these experiments, we confirmed that SnO₂:F by itself is not a suitable TCO for nc-Si:H cells, but found that SnO₂:F overcoated with TiO₂ followed by ZnO was the most effective superstrate for this type of cell.

Thin film photovoltaic applications typically require a front surface transparent conductive oxide (TCO). The most commercially successful TCO for photovoltaic applications has been fluorine doped tin oxide. Fluorine doped tin oxide is easily processed, mechanically durable, heat resistant, stable, and has controllable morphology. Tin oxide can be deposited during the glass manufacturing process, providing high performance coatings for an excellent value. Recent developments in this field include conductivity shifting coatings, and multi-textured morphologies.

A Filtered Cathodic Vacuum Arc (FCVA) thin film deposition system has been used to create Al₂O₃/Al/Al₂O₃ trilayer antireflection coatings on silicon. X-ray photoelectron spectroscopy was used to verify the stoichiometry of the deposited alumina. The optical properties of the deposited Al₂O₃ and Al have been examined using variable angle spectroscopic ellipsometry. The complex refractive index functions of the antireflection coating components were determined. Optical thin film software was used to optimise the required thicknesses of each of the layers in order to achieve minimum perpendicular reflection on silicon across the optical spectrum. The simulations showed that the thickness of the Al layer was critical and the required layer thickness was less than 10 nm. Antireflection coatings with various Al layer thicknesses were deposited and characterised. The microstructure of the coatings was examined, in detail, using cross sectional transmission electron microscopy. Reflectance measurements on the deposited coatings were also performed, with the optimised antireflection coating (with an Al layer thickness of 6 nm) achieving an average reflectance of 4% on silicon over the optical spectrum. The FCVA deposited trilayers are mechanically robust, easy to fabricate and exhibit high performance.

Spherical silicon photovoltaic devices are bonded to flexible substrates to produce light-weight flexible solar modules. In order to maximize the conversion efficiency, the optical loss must be minimized. The concept of conventional anti reflection coating (ARC) does not directly apply to the spherical device due to different geometry. The optimum design of the ARC must maximize the optical power transmission from air to the Si crystal bulk. In addition to the refractive index and the thickness of the ARC, the power distribution on the exposed spherical surface, incidence angle dependent reflection, and multiple reflections at the spherical air-ARC and ARC-silicon interfaces also influence the ARC design. The effects of the spherical shape on the variations of the reflection are analyzed. It is shown that the optimum design is essentially different from the conventional ARC with uniform quarter-wavelength thickness. It is required that the design compensates the effect of variation of the incidence angle across the spherical surface. To achieve this, the thickness should have a zenith-angle dependence. Chemical vapor deposition techniques can potentially be employed for the deposition of the designed films.

In this work, we investigated the temperature dependence of wide bandgap hydrogenated amorphous silicon (a-Si:H)-based, hydrogenated amorphous silicon oxide (a-SiO:H)-based single-junction and hydrogenated protocrystalline silicon/hydrogenated microcrystalline silicon (pc-Si:H/μc-Si:H) double-junction solar cells in order to develop solar cells which are suitable for use in high temperature region. Photo J-V characteristics were measured under AM 1.5 illumination at ambient temperature in the range of 25-75 ^oC. We found that, the values of temperature coefficient for conversion efficiency (TC for η) of both single- and double-junction solar cells were inversely proportional to the initial open-circuit voltage (V_oc). In case of p-i-n single-junction solar cells, the typical pc-Si:H and pc-SiO:H solar cells showed the lowest TC for η of -0.21 and -0.14%/^oC, respectively. The smallest TC for η of pc-SiO:H solar cell was attributed to the positive increase in TC for fill factor (FF). The TC for η of typical pc-Si:H/μc-Si:H double-junction solar cells was around -0.35%/^oC with initial η around 10-12%. Since high V_oc pc-Si:H/μc-Si:H double-junction solar cells exhibit low temperature dependence and highly stable η against light soaking, they are promising for use in high temperature regions. In addition, we conclude that solar cells which are suitable for use in high temperature region must be considered both high η with low temperature dependence.

The influence of the cathode electrode on the characteristics of pentacene/perylene derivatives based organic solar cells was analysed by means of absorption, photoluminescence, and X-ray spectroscopies. We report the characteristics of a series of organic solar cells fabricated with Al, Ag, and Au electrodes for the interface between metals and organic semiconductors, which play a central role in the physics of organic solar cells. Donor and acceptor layers of a solar cell were pentacene and N,N'-dioctyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-8C) and N,N'-ditridecyl-3,4,9,10-perylene-tetracarboxylic diimide (PTCDI-13C) respectively. Two organic solar cells with pentacene/PTCDI-8C and pentacene/PTCDI-13C heterojunctions as active layers were fabricated to compare the influence of power conversion efficiency among perylene derivatives with various numbers of carbon molecules by means of J-V measurements. Under the sunlight simulator with an AM1.5G filter and power of 100 mW/cm², the solar cells of the pentacene/PTCDI-13C heterojunction with the Ag cathode had J-V characteristics of short-circuit current density of 0.415 mA/cm², open-circuit voltage of 0.413 V, fill factor of 0.55, and power conversion efficiency of 0.1%, which were better than those of the pentacene/PTCDI-8C heterojunction. Moreover, according to the thin film analysis, the PTCDI-13C thin film's excitons at the interface of the heterojunction for dissociation were more, and the probability of radiative recombination of the electron-hole pair was less than for the PTCDI-8C. The PTCDI-13C thin-film possessed better carrier mobility than PTCDI-8C. Therefore, we could conclude that the factors mentioned above are keys to the pentacene/PTCDI-13C-based solar cells' better power conversion efficiency. The carrier transportation mechanism of these solar cells is discussed clearly.

In this work, key properties of In_xGa_1-xN tandem solar cells (SCs) (single junction, double junctions and triple junctions) were simulated by employing AMPS-1D software, including I-V characteristic, efficiency, band structure, built-in electric field etc. We compared the results of our simulation with the results of other theoretical calculations published in the literature and analysed the causes of the differences among these results. We try to find some useful information related to the important parameters of InGaN SCs, such as the band gap configuration and thickness selection. This work may help the progress in the preparation of the InGaN-based high efficiency solar cells.

CuInse₂ films and related alloys were prepared by thermal evaporation of Cu, InSe and GaSe compounds instead of elemental sources. Band gap tailoring in Cu(In,Ga)Se₂ based solar cells is an interesting path to improve their performance. In order to get comparable results solar cells with Ga/(In+Ga) ratios x =0 and 0.3 were prepared, all with a simple two-step sequential evaporation process. The morphology of the resulting films grown at 550°C was characterized by the presence of large facetted chalcopyrite grains, which are typical for device quality material. It is important to note that absorber films with elemental gallium resulted in a significant decrease in the average grain size of the film. The XRD diffraction pattern of a single-phase Cu(In,Ga)Se₂ films depicts diffraction peaks shift to higher 2θ values compared to that of pure CuInSe₂ . The PL spectrum of Cu(In,Ga)Se₂ thin films also depicts the presence of the peak at higher energy that is attributed to the incorporation of gallium into the chalcopyrite lattice. As the band gap of CIGS increases with gallium content, desirable effects of producing higher open-circuit voltage and low-current density devices were achieved. A corresponding increase in device efficiency with gallium content caused by a higher fill factor was observed. The best results show passive area efficiencies of up to 10.2% and open circuit voltage (V_oc) up to 519 mV at a minimum band gap of 1.18eV.