High efficiency CdTe/CdS thin film solar cells with Sb2Te3 back contact by a thoroughly dry process

In this paper, a completely dry process suitable to prepare stable and efficient CdS/CdTe thin film solar cells is described. In order to obtain high efficiency solar cells, the absorber layer, namely CdTe, needs to be treated at 400°C in presence of CdCl2. This process is generally done in air in which some oxides form on the CdTe surface. A back contact made directly on the oxidized surface cannot work well. For this reason and also to prepare a suitable CdTe surface, an etching in Br-methanol or in a mixture of acids is generally done. In our case we avoided the etching by treating CdTe with CdCl2 in pure Ar and by removing the residual CdCl2 with a slight annealing at 400°C in vacuum.