Impurity analysis of CdCl2 used for thermal activation of CdTe-based solar cells.

We present an impurity analysis of cadmium chloride (CdCl2) using inductively coupled plasma mass spectrometry. Six batches of CdCl2 with different nominal purity ranging from 99.999% to 95% were analysed. Each batch turned out to be different in terms of the nature and concentration of impurities. However, all batches generally contained four impurity elements present with concentrations that were characteristic for that element, these being Na (~25 ppm (parts per million)), In (< 1 ppm), Pb (~0.5 ppm) and Te (< 3 ppm), regardless of the nominal purity or the supplier. In all the batches investigated, the major part of the impurities detected (between 83% and 91%) was found to comprise potentially electrically active dopants in CdTe. These impurities are therefore of importance to CdTe/CdS thin film solar cells, where the thermal activation is based on the use of CdCl2