Development of a CdCl2 thermal treatment process for improving CdS/CdTe ultrathin solar cells

Abstract

Magnetron Planar Sputtering (MPS) is an appropriate deposition technique for ultrathin (UT) solar cells fabrication. This technique is compatible with deposition of many materials which are relevant for the preparation of thin film cells, including p-type CdTe and CuInGaSe2, and n-type CdS as a window partner material. Therefore, MPS enables the sequential (and scalable) deposition of uniform SnO2, CdS, and CdTe films. Unfortunately, the conventional CdCl2 treatments required for making good and highly efficient solar cells cause problems related to the very thin layers used in the case of UT devices. Hence, this work focuses on the evaluation of an effective CdCl2 thermal treatment specifically developed for UT CdS/CdTe cells made by MPS. The results for the XRD, UV–Vis, and SEM characterizations of the CdTe absorber material, before and after the CdCl2 treatment, as well as the performance measurements for the fabricated solar cells are reported. It is shown that the UT cells thermally treated, with CdCl2 deposited by close space vapor transport/CSVT), improve their performance by about 85% as compared to non-treated cells.