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Tolerance of Three-Stage CIGS Deposition to Variations Imposed by Roll-to-Roll Processing: Final Technical Report, May 2003 - September 2005

Description: Three-stage co-evaporation of CIGS imposes stringent limits on the parameter space if high-efficient devices are to result. Substrate temperatures during the 1st stage (as well as during the 2nd and 3rd stage), Se partial pressure, and amount of Na supplied are critical for good nucleation, proper In-Ga-selenide precursor phase, and diffusion of Cu into the precursor, as well as diffusion of Ga through the film. In addition, the degree of Cu-rich excursion impacts maximum performance and process tolerance. Enveloping the above is the basic time-temperature profile inextricably linked to the metals delivery rates. Although high-efficiency, three-stage deposited CIGS devices on the R&D scale are grown at about 20-45 minutes to thicknesses of 2 to 2.5 m, the latter is not a viable approach for an economic manufacturing process. At Global Solar Energy, Inc., CIGS films are typically grown in about 6 minutes to thicknesses of less than 2 m. At the same time, the emissivity and thermal conductivity of stainless steel is vastly different from that of glass, and the reduced growth time poses restrictions on the substrate temperature ramp rates and diffusion of species (reaction kinetics). Material compatibility in the highly corrosive Se environment places limitations on the substrate heaters; i.e., substrate temperatures. Finally, one key advantage of a RTR deposition approach (compact equipment) restricts post CIGS Se exposure and cool-down rates to be vastly different than those practiced in the laboratory.
Date: January 1, 2006
Creator: Beck, M. E. & Britt, J. S.
Partner: UNT Libraries Government Documents Department

CIS Photovoltaic Technology; Final Technical Report

Description: This report describes work performed by Energy Photovoltaics, Inc. (EPV) during the third phase of a three-phase, cost-shared subcontract. Researchers at EPV explored novel sequential formation recipes for CIGS that can be implemented on a unique pilot line constructed to coat low-cost, glass substrates 4300 cm2 in area; implemented a particular CIGS recipe on the pilot line that enabled large-area modules to be prepared with efficiencies up to 7.6%; and performed electrical resistance monitoring of the film that proved capable of indicating the temperature of compound formation and detecting termination. The substrate/Mo/Na working group (which included EPV, NREL, and others) studied Na in Mo and the effect of Na on devices, and found it beneficial except at concentrations exceeding 0.4%. Researchers determined the following properties of large-area, magnetron-sputtered ZnO:Al: sheet resistance 24 W/sq., transmission 82%, conductivity 440 S cm-1; and preheating the glass increases the conductivity. Devices prepared using a baseline CIGS process averaged 11.7% in efficiency. Modules and minimodules were prepared using a diode-laser-pumped yttrium-aluminum-garnet laser for the Mo patterning and mechanical scribing for the cuts. Large-area CIGS formation involves the use of linear sources, and thickness profiles were presented for simple and optimized linear sources. An unencapsulated module producing 25 watts (7.65% aperture-area efficiency) was produced. Using a new diagnostic technique, the fill factor of a CIGS module was decomposed into contributions from the intrinsic device fill factor and ZnO sheet resistance.
Date: October 28, 1998
Creator: Delahoy, A. E.; Britt, J. S. & Kiss , Z. J.
Partner: UNT Libraries Government Documents Department

CIS photovoltaic technology. Annual technical report, January 12, 1995--January 11, 1996

Description: EPV`s overall strategy in developing CIGS photovoltaic technology has been to define and construct a flexible set of large area vacuum deposition equipment and to explore CIGS formation recipes that can be implemented on this equipment. This is the inverse of the conventional approach in which manufacturing techniques are sought that can reproduce a high efficiency laboratory scale process over large areas. A feature of this equipment is the use of proprietary linear sources capable of downwards evaporation. Using recipes generated within this program, CIGS cells with efficiencies up to 13.9% were prepared by EPV under a separate CRADA with NREL. Entirely within this program, an aperture area efficiency of 9.6% was achieved for a laminated submodule of area 135.2 cm{sup 2}. Considerable effort has gone into the preparation and characterization of CIGS prepared on substrates measuring 96.5 cm x 44.5 cm, and good compositional uniformity has been achieved along both the short and long directions of the plate. Despite this, the material has not yet achieved the efficiency levels demonstrated in smaller scale equipment, and recipe development is ongoing. As part of a program to eliminate, if possible, the use of CdS, alternative buffer layers such as InSe, In{sub x}S{sub y}, and ZnSe have been explored, and, to gain insight into junction formation, CdSe. Of these compounds, ZnSe has shown the most promise, and further experiments are being conducted to optimize material and device properties.
Date: June 1, 1996
Creator: Delahoy, A.E.; Britt, J.S. & Gabor, A.M.
Partner: UNT Libraries Government Documents Department

CIS photovoltaic technology. Annual technical report, January 12, 1996--January 11, 1997

Description: Thin film photovoltaic modules based on Cu(In,Ga)Se{sub 2} have been shown to possess attributes that should enable them to compete effectively with silicon-based modules, and that should ultimately allow realization of a much lower $/Wp cost figure. These attributes are stability, high efficiency, and low materials cost. Energy Photovoltaics has explored novel CIGS formation recipes that can be implemented on a unique pilot line constructed to coat substrates 4300 cm{sup 2} in area. One particular feature of this line is the use of proprietary linear sources capable of downwards evaporation. After experimentation with several types of recipe, a so-called {open_quotes}hybrid{close_quotes} process was found to simultaneously yield the desired combination of properties, namely good adhesion, device efficiency, uniformity, and reproducibility. The steps involve precursor formation, compound formation, and termination. Diagnostic techniques used to study and improve the CIGS films included spatial mapping of thickness, composition (using Auger analysis), resistance, V{sub oc} and I{sub sc}. The last three items are determined by quick tests designed to provide rapid feedback on plate quality. Problem areas were broken down and isolated through use of techniques involving substitution of different pieces of equipment for certain processing steps. For example, pilot line precursors were selenized in both the pilot line and smaller scale R&D equipment.
Date: June 1, 1997
Creator: Delahoy, A.E.; Britt, J.S. & Kiss, Z.J.
Partner: UNT Libraries Government Documents Department