Enhancing Li tolerance via Ag doping in high-efficiency CZTSSe solar cells

Element doping has been widely recognized as an important strategy for improving the power conversion efficiency (PCE) of kesterite (CZTSSe) solar cells. Single-element doping has demonstrated substantial improvements in device performance. Therefore, multi-element doping strategies, utilizing the unique properties of individual dopants, have recently attracted significant attention. However, most of co-doping studies predominantly focused on the individual effects of doping elements on CZTSSe thin films, often overlooking the potential interactions between co-doping elements, thus limiting the development of the solar cells. In this study, we systematically investigated the optimal concentration of Li–Ag co-doping strategy and discovered that the incorporation of Ag effectively enhanced the thin film tolerance to higher Li doping concentration. The formation of dense upper grains following Ag doping suppressed the rapid Se diffusion rate during the initial reaction stages, thereby mitigating the deterioration of thin-film quality induced by excessive Li doping which is often considered to deteriorate the PCE of CZTSSe solar cells. Through precise control of doping concentrations (8% Li and 5% Ag), we achieved a remarkable PCE of 13.42%. This study underscores the critical importance of considering dopant interactions in multi-element doping strategies, providing new insights for the development of thin film solar cells.