High Throughput, Low Toxic Processing of Very Thin, High Efficiency CIGSS Solar Cells: Final Report, December 2008

The work carried out during this project presents the use of diethylselenium or other organometallic precursors as low-toxicity alternative selenium sources for preparing a high-quality absorber

CIGSS Thin Film Solar Cells: Final Subcontract Report, 10 October 2001-30 June 2005

This report describes the I-III-VI2 compounds that are developing into a promising material to meet the energy requirement of the world. CuInSe2 (CIS) and its alloy with Ga and S have shown long-term stability and highest conversion efficiency of 19.5%. Among the various ways of preparing CuIn1-xGaxSe2-ySy (CIGSS)/CdS thin-film solar cells, co-evaporation and sputtering techniques are the most promising. Sputtering is an established process for very high-throughput manufacturing. ARCO Solar, now Shell Solar, pioneered the work in CIS using the sputtering technique. The two-stage process developed by ARCO Solar involved sputtering of a copper and indium layer on molybdenum-coated glass as the first step. In the second step, the copper-indium layers were exposed to a selenium-bearing gas such as hydrogen selenide (H2Se) mixed with argon. The hydrogen selenide breaks down and leaves selenium, which reacts and mixes with the copper and indium in such a way to produce very high-quality CIS absorber layer. Sputtering technology has the added advantage of being easily scaled up and promotes roll-to-roll production on flexible substrates. Preliminary experiments were carried out. ZnO/ZnO:Al deposition by RF magnetron sputtering and CdS deposition by chemical-bath deposition are being carried out on a routine basis

Comparison of Minority Carrier Lifetime Measurements in Superstrate and Substrate CdTe PV Devices: Preprint

We discuss typical and alternative procedures to analyze time-resolved photoluminescence (TRPL) measurements of minority carrier lifetime (MCL) with the hope of enhancing our understanding of how this technique may be used to better analyze CdTe photovoltaic (PV) device functionality. Historically, TRPL measurements of the fast recombination rate (t1) have provided insightful correlation with broad device functionality. However, we have more recently found that t1 does not correlate as well with smaller changes in device performance, nor does it correlate well with performance differences observed between superstrate and substrate CdTe PV devices. This study presents TRPL data for both superstrate and substrate CdTe devices where both t1 and the slower TRPL decay (t2) are analyzed. The study shows that changes in performance expected from small changes in device processing may correlate better with t2. Numerical modeling further suggests that, for devices that are expected to have similar drift field in the depletion region, effects of changes in bulk MCL and interface recombination should be more pronounced in t2. Although this technique may provide future guidance to improving CdS/CdTe device performance, it is often difficult to extract statistically precise values for t2, and therefore t2 data may demonstrate significant scatter when correlated with performance parameters

Structural and electronic properties of Pb1-xCdxTe and Pb1-xMnxTe ternary alloys

A systematic theoretical study of two PbTe-based ternary alloys, Pb1-xCdxTe and Pb1-xMnxTe, is reported. First, using ab initio methods we study the stability of the crystal structure of CdTe - PbTe solid solutions, to predict the composition for which rock-salt structure of PbTe changes into zinc-blende structure of CdTe. The dependence of the lattice parameter on Cd (Mn) content x in the mixed crystals is studied by the same methods. The obtained decrease of the lattice constant with x agrees with what is observed in both alloys. The band structures of PbTe-based ternary compounds are calculated within a tight-binding approach. To describe correctly the constituent materials new tight-binding parameterizations for PbTe and MnTe bulk crystals as well as a tight-binding description of rock-salt CdTe are proposed. For both studied ternary alloys, the calculated band gap in the L point increases with x, in qualitative agreement with photoluminescence measurements in the infrared. The results show also that in p-type Pb1-xCdxTe and Pb1-xMnxTe mixed crystals an enhancement of thermoelectrical power can be expected.Comment: 10 pages, 13 figures, submitted to Physical Review

Diagnostic analysis of silicon photovoltaic modules after 20-year field exposure,”

ABSTRACT The objective of this study was to investigate the technology used by Spectrolab Inc. to manufacture photovoltaic modules that have provided twenty years of reliable service at Natural Bridges National Monument in southeastern Utah. A field survey, system performance tests, and a series of module and materials tests have confirmed the durability of the modules in the array. The combination of manufacturing processes, materials, and quality controls used by Spectrolab resulted in modules that have maintained a performance level close to the original specifications for twenty years. Specific contributors to the durability of the modules included polyinyl-butyral (PVB) encapsulant, expanded metal interconnects, silicon oxide anti-reflective coating, and excellent solder/substrate solderability

Studies On Chemical Bath Deposited Cadmium Sulphide Films By Buffer Solution Technique

Cadmium sulphide films were grown by a chemical bath technique using cadmium acetate and cadmium chloride as the Cd ion source and thiourea as the sulphur source. The solution growth process was carried out with and without buffer solutions containing ammonium acetate and ammonium chloride onto glass substrates. Various properties of the films such as surface morphology, crystallinity, composition, optical properties and dark resistivities were compared for both the above techniques. © 1995 Chapman & Hall

Spectroscopic Analysis Of Cigs2/Cds Thin Film Solar Cell Heterojunctions On Stainless Steel Foil

This paper presents a spectroscopic analysis of the interface between a CuIn1-xGaxS2 (CIGS2) absorber and a CdS buffer layer on stainless steel foil by Auger electron spectroscopy (AES), inverse photoemission spectroscopy (IPES) and photoelectron spectroscopy (PES) such as X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). By combining these spectroscopic techniques, detailed information about the electronic and chemical properties of the CIGS2 surface and the CdS/CIGS2 interface can be obtained. The gallium concentration in CIGS2 films was found to increase continuously towards the Mo back contact. XPS analysis showed the presence of KCO3 on the surface of CdS, deposited on etched and un-oxidized samples indicating diffusion of potassium. No potassium was observed on oxidized as well as samples having thicker CdS (50 nm) indicating the effectiveness of oxidation and chemical bath deposition (CBD) process in cleaning the sample surface effectively. In addition, investigation of the electronic level alignment at the interface has been carried out by combining PES and IPES. Conduction band offset of -0.45 (±0.15) eV and a valence band offset of -1.06 (±0.15) eV were measured. These unfavorable conditions limit efficiency of CIGS2 thin film solar cells. © 2005 Elsevier Ltd. All rights reserved

Comparison Of Band Alignments At Various Cds/Cu(In,Ga)(S,Se)2 Interfaces In Thin Film Solar Cells

The band alignment at the CdS/Cu(In,Ga)(S,Se)2 interface, as derived in our earlier publications, are compared for different absorber compositions. The discussed band alignments were directly determined using a combination of UV- and x-ray photoemission and inverse photoemission. While a flat conduction band alignment can be found for low-gap material, the cell structure with a high-gap absorber shows a cliff-like alignment. The different alignments can be correlated with the respective cell parameters, explaining why the expected linear gain in open circuit voltage for the high-gap absorbers has not yet been achieved. © 2006 IEEE

Low Temperature Surface Passivation Of Silicon Solar Cells

Low temperature surface passivation is a process that has a potential to reduce the input energy cost of the solar cell with minimum modification of the manufacturing bed, while keeping the efficiency, and life of the cells within acceptable range of values. In this review, low temperature deposition methods of SiO2, Al2O3, a-Si:H, silicon nano particles (NPs), and organic materials, are considered. Surface recombination velocities, defect densities, stability of these passivating layers are discussed along with the mechanisms of passivation on Si surface

Low Temperature Surface Passivation Of Silicon Solar Cells

Low temperature surface passivation is a process that has a potential to reduce the input energy cost of the solar cell with minimum modification of the manufacturing bed, while keeping the efficiency, and life of the cells within acceptable range of values. In this review, low temperature deposition methods of SiO2, Al2O3, a-Si:H, silicon nano particles (NPs), and organic materials, are considered. Surface recombination velocities, defect densities, stability of these passivating layers are discussed along with the mechanisms of passivation on Si surface