On the Origins of Impurities in CdTe-Based Thin Film Solar Cells

Abstract

AbstractWe present a multi-element study of impurities in CdTe/CdS photovoltaic cells, aimed at understanding their origins and impact on devices. Our investigation was based on calibrated secondary ion mass spectrometry (SIMS) depth profiling, with Na, Zn, Sn, O, Sb, Si, Cl, In, Cu and Pb being studied. The solar cell structures were grown by sputtering and close-space sublimation, and some of them were further processed (CdCl2 and Br2-methanol) for the purpose of comparison. Using source materials of different purity allowed us to establish the origins of impurities. We found that some elements increased in concentration upon processing, namely Cl (x100), Na (x10), and In (x1.5). The concentrations of Si, Cu, Zn, Sn and Sb found in a processed device were largely unchanged - and are similar to those found in a high purity single crystal CdTe reference sample.