Photovoltaic Properties of Cu2S–CdS Heterojunctions

Abstract

The photovoltaic properties of Cu₂S–CdS heterojunctions have been compared before and after short heat treatment, using measured I‐V characteristics, junction capacitance, and spectral response. After heat treatment slow transients in the photoresponse and effects of secondary illumination were investigated. Optical quenching of the photocurrent was observed in two ir bands corresponding to transitions at 0.8 and 1.1 eV, and enhancement of the photocurrent was seen for hv>1.5 eV. Long persistence of the enhancement effect was observed, which thermally quenched with an activation energy of 0.95 eV. A model for the heterojunction is proposed in which hole trapping in deep imperfection centers in the CdS near the junction is the key mechanism. A conduction band spike is assumed to exist at the Cu₂S–CdS interface. The transparency of this spike to photoexcited electrons diffusing from the Cu₂S is modulated by variations in the CdS depletion width caused by the deep trapping.