Photovoltaic properties of n-CdS/p-Cu 2Te thin film heterojunctions

Abstract

Cu 2Te is an important material for solar energy conversion. Cu 2Te films (0.5−2.0 microm) 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 A ̊ ). The grain size was of the order of 0.5–0.6 microm. The electrical conductivity was 100–300Ω −1cm −1 and the films exhibited p-type conduction. Hall mobilities of 30−70cm 2V −1s −1 were obtained and the thermoelectric power ranged from 0.16 to 0.60m V K −1. The optical energy gap was 1.08−1.10 eV and the absorption coefficient lies in the range (0.7−7.5) × 10 5 cm −1. These low resistivity polycrystalline p-Cu 2Te films have been used as an absorber layer in the fabrication of p-Cu 2Te/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 12.2mA cm −2 and an electrical conversion efficiency of 6.0% have been obtained for a 1 cm 2 area cell under a solar input of 70 mW cm −2.