Investigation of Cu-doping effects in CdTe solar cells by junction photoluminescence with various excitation wavelengths

Abstract

Cu-doping effects and a CdSxTe1−x mixed crystal layer in CdS/CdTe solar cells were investigated on the basis of the photoluminescence (PL) of the CdS/CdTe junction using excitation lights incident on the glass substrate side (junction PL) with various excitation wavelengths. In the Cu-doped CdS/CdTe solar cells, broad emissions at 910–950 nm, which were probably caused by donor–acceptor pair (DAP) emission between CuCd acceptors and ClTe donors, were observed. The intensity of the junction PL markedly increased owing to the Cu doping. This result suggests that the intensity of junction PL is relevant to the conversion efficiency of CdTe solar cells. Furthermore, the PL peak energy increased with increasing excitation wavelength. This result indicates that the CdSxTe1−x mixed crystal layer is formed in the CdS/CdTe interface, and that the S composition decreased from the CdS/CdTe interface to the rear.