Studies on the influence of etching solution on the properties of Cu2ZnSn(S, Se4) thin film solar cells

Cu2ZnSn(S, Se)(4) (CZTSSe) thin film solar cells (TFSCs) have emerged as the most promising low-cost alternatives to well-established CuInGaS2 and CuInS2-based TFSCs technologies. The surface composition of the absorber layer and the interface quality between the absorber and buffer layers play a key role in the performance of CZTSSe TFSCs. In this study, we investigated the influence of different etchants namely potassium cyanide (KCN), hydrochloric acid (HCl) and ammonia on different properties such as structural, morphological, and compositional as well as the solar cell performance of CZTSSe TFSCs. The results revealed no significant changes in the film structural properties before and after etching with any of the tested etchants. However, the slight changes in the composition and microstructure were observed after etching treatment. The microstructure was improved after KCN treatment with larger grain size compared to absorber layer without etching, whereas the slightly distorted microstructure with several surface pinholes was observed after HCl and ammonia treatment. Surprisingly, HCl and ammonia treatments degraded the open circuit voltage and fill factor values and thereby decreasing the power conversion efficiency (PCE) of the CZTSSe TFSCs. On the other hand, KCN treatment slightly improved the PCE of CZTSSe TFSCs. The decreased PCE after HCl and ammonia treatments could be mainly attributed to the deteriorated absorber quality as well as poor formation of poor juction between the absorber layer and the CdS buffer layer.