Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition: Annual Technical Report

During the past year, Colorado School of Mines (CSM) researchers performed systematic studies of the growth and properties of electrodeposition CdS and back-contact formation using Cu-doped ZnTe, with an emphasis on low Cu concentrations. CSM also started to explore the stability of its ZnTe-Cu contacted CdTe solar cells. Researchers investigated the electrodeposition of CdS and its applicationin fabricating CdTe/CdS solar cells. The experimental conditions they explored in this study were pH from 2.0 to 3.0; temperatures of 80 and 90 deg. C; CdCl2 concentration of 0.2 M; deposition potential from -550 to -600 mV vs. Ag/AgCl electrode; [Na2S2O4] concentration between 0.005 and 0.05 M. The deposition rate increases with increase of the thiosulfate concentration and decrease of solutionpH. Researchers also extended their previous research of ZnTe:Cu films by investigating films doped with low Cu concentrations (<5 at. %). The low Cu concentration enabled us to increase the ZnTe:Cu post-annealing temperature without causing excessive Cu diffusion into CdTe or formation of secondary phases. The effects of Cu doping concentration and post-deposition annealing temperature on thestructural, compositional, and electrical properties of ZnTe were studied systematically using X-ray diffraction, atomic force microscopy, electron microprobe, Hall effect, and conductivity measurements.