Effect of CdCl2 annealing treatment on CdS thin films and CdTe/CdS thin film solar cells

In order to study the effect of CdCl2 annealing treatment on thin CdS films and CdTe/CdS thin film solar cells, a comparative study was carried out on three types of CdTe/CdS solar cells, which had different kinds of CdS window layer: as-deposited CdS, air-annealed CdS without CdCl2 pre-coating, and CdCl2-annealed CdS. When annealed in air the CdS film was partially oxidated to CdO and CdSO4. These oxides increased the series resistance of the CdTe solar cell and led to the lowest fill factor. The presence of CdCl2 on the surface of a CdS thin film during heat treatment in air protected it from oxidation and promoted the recrystallization of the CdS film, resulting in large and closely packed grains with a grain size of similar to 50-150 nm. CdTe/CdS solar cell with such a kind of CdS window layer showed the largest short circuit current and highest conversion efficiency of 12.4%. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim