The structural changes in CdS-CdTe thin films due to annealing

Thin film solar cells based upon CdS-CdTe heterojunctions have become an im portant alternative to silicon based devices. The film structures formed du ring fabrication are critical to cell efficiency and thus their study is fu ndamental to improving device performance. We have used synchrotron x-ray d iffraction to investigate the effect of a post deposition anneal upon the f ilm structures and, in particular, have examined the dynamic formation of i ntermixed regions adjacent to the original, metallurgical interface. Our re sults have enabled us to produce a dynamic model for the structural changes which includes the extent of interdiffusion. We show that, for a 400 nm Cd Te film in the presence of chlorine, the original CdS and CdTe layers are c ompletely transformed into layers with average compositions CdS0.93Te0.07 a nd CdTe0.94S0.06, respectively. We present evidence that the interdiffusion occurs during or following a recrystallization and that, to a limited exte nt, these changes also occur without chlorine.