Photovoltaic Properties of Reactively Sputtered Cu/sub x/S--CdS Heterojunctions

摘要

The use of sputtering techniques as an attractive means of fabricating low-cost thin film solar cells has been studied for the Cu/sub x/S-CdS heterojunction system. Control of the Cu/sub x/S stoichiometry is done using variable partial pressures of H sub 2 S in a reactive sputtering mode with excellent results. Measured optical absorption spectra, film resistivity, and x-ray diffraction analysis verify the consistent formation of chalcocite. TEM electron diffraction studies indicate epitaxial formation of the reactively sputtered Cu/sub x/S on CdS consistent with a measured interface recombination velocity, S/sub I/, of 2 x 10 exp 5 cm/sec. Cell forward and reverse I-V characteristics are also dominated by tunneling processes, as has been observed for wet-dip Cu/sub x/S-CdS heterojunctions. Measured minority carrier diffusion lengths, L/sub e/, of equal to or greater than 1000 A in the Cu/sub x/S, coupled with significant red response of heterojunction cells, verify the suitability of reactively sputtered Cu/sub x/S for efficient cell fabrication. Cell efficiencies of 4% have been obtained and are limited at present by technological factors including cell shorting and surface roughness problems. (ERA citation 03:052250)