Effect of CdCl2 activation on the impurity distribution in CdTe/CdS solar cell structures

CdTe/CdS/In2O3:F/glass solar cell structures made using 7N CdTe were investigated to determine the distribution of impurities. This study was carried out using quantitative secondary ion mass spectrometry (SIMS) profiling from the CdTe surface through the glass substrate. Particular emphasis was placed on the potential for electrically active impurities to originate from the cadmium chloride (CdCl2) processing step, since such impurities are likely to affect the CdTe/CdS device performance. The impurities: Cl, O, Cu, Na, In, Sb, Sn, Si, Zn, Pb and S were profiled for as-grown and CdCl2 treated structures. Ion implanted CdTe and CdS standards were used for SIMS quantification. It has been shown that O and Cu do not originate from the CdCl2 activation process. Zn, Sn and Pb are also invariant on processing. Other impurities such as Cl, Na and Sb are definitely present in the activated structures due to their presence in the CdCl2 starting material used in the treatment. Si diffusion from the glass substrate as well as Te and S interdiffusion at the CdTe/CdS interface following the CdCl2 treatment were also highlighted.