Effect of CdCl2 Treatment on the Interior of CdTe Crystals

Abstract

ABSTRACTAn essential processing step in CdTe/CdS polycrystalline solar cells is heat treatment in CdCl2. We present photoluminescence results from single crystals of CdTe that have been exposed to CdCl2 treatments at 387 C similar to those used in actual cell fabrication. Using sub band gap excitation from a tunable diode laser, we probe states in the interior of the crystal. We show that high-purity (99.998 percent) CdCl2 treatment results in the appearance of a 1.45 eV donor-acceptor transition that is likely due to a Cl-Cu center. Low purity (99.7 percent) CdCl2treatment results in the appearance of the 1.45 eV line and a 1.555 eV Cu-related emission. These results indicate that the CdCl2 treatment has an effect on the interior of CdTe grains, in addition to its already well established effect on grain boundaries in polycrystalline CdS/CdTe devices. They also imply that CdCl2 treatment may result in the incorporation of Cu into the CdTe grains. The results will be related to the effects of CdCl2 on polycrystalline CdS/CdTe devices that have been observed by other groups.This work is supported by NREL