Development of a Low Cost Insulated Foil Substrate for Cu(InGaSe)2 Photovoltaics

Abstract

EXECUTIVE SUMMARYThe present project validated the use of stainless steel flexible substrate coated with silicone-based resin dielectric, developed by Dow Corning Corporation, for Cu(InGa)Se 2 based photovoltaics. The project's driving force was the high performance of Cu(InGa)Se 2 based photovoltaics coupled with potential cost reduction that could be achieved with dielectric coated SS web substrate.First, 430SS was shown to be the preferred substrate based on the suitable thermal expansion coefficient. However, randomly distributed shunt paths through the siliconebased resin had to be burned with voltage pulses for module fabrication. Reducing the density of the shunt paths through changes in the process and locating and burning the remaining ones has resolved the issue for the project. However this process of shunt burning may be problematic in a manufacturing environment.On vapor deposited films of Cu(InGa)Se 2, small area cell efficiency of more than 15% has been obtained with Cu(InGa)Se 2 thickness as small as 1.2 m. For Cu(InGa)(SSe) 2 films obtained by precursor selenization, efficiencies of more than 12% were demonstrated. However, in this process, transitioning from glass substrate to an SS based one is believed to require a different and robust approach.Uniformity of the device performance was shown on a 6 feet roll-to-roll PVD deposited Cu(InGa)Se 2 . The central 4 ft of the web, when sampled every foot, provided devices with high efficiencies of more than 12% with Cu(InGa)Se 2 thickness of 1.4 m.Throughput up to 3 and 6 inches/min web speeds resulted in efficiencies in the range of 9 to 11% with an absorber thickness of around 1 m.The work on module fabrication was challenging in some respects. All laser monolithic integration has been a difficult problem that requires further work and more innovative solutions.