PHOTOVOLTAIC PROPERTIES OF N-CDS/P-CU2TE THIN-FILM HETEROJUNCTIONS

Cu2Te is an important material for solar energy conversion. Cu2Te films (.0.5-2.0-mu-m) prepared by flash evaporation technique onto Corning 7059 glass substrates kept at 523 K were nearly stoichiometric and polycrystalline with a cubic structure (a = 6.72 angstrom A). The grain size was of the order of 0.5-0.6-mu-m. the electrical conductivity was 100-300-OMEGA-1 cm-1 and the films exhibited p-type conduction. Hall mobilities of 30-70 cm2 V-1 s-1 were obtained and the thermoelectric power ranged from 0.16 to 0.60 mVK-1. The optical energy gap was 1.08-1.10eV and the absorption coefficient lies in the range (0.7-7.5) x 10(5)cm-1. These low resistivity polycrystalline p-Cu2Te films have been used as an absorber layer in the fabrication of p-Cu2Te/n-CdS (doped with 1.5 at.% In) thin film heterojunction solar cell. The current density-voltage, capacitance-voltage and spectral response of these junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 560mV, a short-circuit current density of 12.2mAcm-2 and an electrical conversion efficiency of 6.0% have been obtained for a 1 cm2 area cell under a solar input of 70mW cm-2.