An efficient Li+-doping strategy to optimize the band alignment of a Cu2ZnSn(S,Se)4/CdS interface by a Se&LiF co-selenization process

A Li+-doping strategy is a promising route for achieving highly efficient Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic devices with a large grain absorber layer, high p-type carrier concentration and good band alignment at the Cu2ZnSn(S,Se)4/CdS interface. However, Li+-doped CZTSSe solar cells based on in situ and pre-deposition doping strategies reported thus far generally suffer from massive lithium losses and sodium rejection due to the soda-lime glass substrate. Therefore, simultaneously fulfilling the goals of simple and efficient Li+-doping remains a major technical challenge, which may be addressed, as we demonstrate here, with the development of a Se&LiF co-selenization process. By engineering the band alignment of the Cu2ZnSn(S,Se)4/CdS interface through the Se&LiF co-selenization process, an encouraging efficiency of 11.63% with an open-circuit voltage deficit of 0.583 V has been reached. Furthermore, the crystallinity of the absorber layer and the distribution of copper are improved, and a more copper-poor CZTSSe surface is formed. This novel Li+-doping strategy introduces a new approach towards the goal of high-performance CZTSSe solar cells compatible with a simple manufacturing process and excellent performance.