Photovoltaic device performance of electron beam evaporated Glass/TCO/CdS/CdTe/Au heterostructure solar cells

Abstract

We report on substrate temperature and Cu addition induced changes in the photovoltaic device performance of Glass/TCO/CdS/CdTe/Au heterostructures prepared by the electron beam evaporation technique. Prior to the photovoltaic study, the structural and optical properties of CdTe, CdTe:Cu and CdS/CdTe, CdS/CdTe:Cu layers were studied. X-ray diffraction (XRD) analysis showed that the deposited films belong to a zinc blende structure. The existence of the Te peak in the XRD pattern revealed the presence of excess Te in the deposited film structures, which confirmed the p-type conductive nature of the films. This was further substantiated by the electrical study. The low resistivity of 1 × 103 Ω cm was obtained for 4 wt.% of the Cu-doped CdTe film, which may be due to the substitutional incorporation of more efficient Cu2+ (Cd2+) into the CdTe lattice. The decrease in band gap with increasing Cu content may be attributed to the existence of shallow acceptor level formed by the incorporation of Cu into the CdTe lattice. The efficiency of the cell was increased with increasing Cu concentration and the cell prepared at room temperature with 4 wt.% of Cu addition possessed the maximum conversion efficiency of 1.68%. Further, a good photoresponse of the device is achieved as the Voc and Isc are increased with increase in the input power. Keywords: CdTe, Grain boundary effect, Optical tailoring, Recombination losses, Ideality factor, Parasitic resistances, Conversion efficiency