Nanoscale Surface Electrical Properties Tailored by Room‐Temperature Sulfurization for High‐Efficient CZTSe Solar Cells

Abstract

AbstractSurface sulfurization can tailor the energy band alignment between p–n heterojunction for the kesterite‐structured Cu2ZnSnSe4 (CZTSe) solar cells. However, the traditional high‐temperature sulfurization process result in the decomposition of kesterite film and thus introducing deep defects. Room‐temperature surface sulfurization, which do not introduce new deep defects during the sulfurization process, is a good method for sulfurization. Combined by different experimental techniques, in this study, it is found that CZTSe film etched by concentrated ammonia can not only tailor the surface nanoscale composition, but also make CZTSe film to expose more crystallographic sites for the successful surface sulfurization. The conductivity of grains and grain boundaries for the absorber layer is improved, the minority carrier lifetime is increased, and the interface band alignment is modified by reducing the conduction band offset successfully after following (NH4)2S vapor treatments, which drive the improvement of the open‐circuit voltage (VOC) of the solar cell from 376 to 430 mV. This work can direct the surface bandgap engineering with nontraditional sulfurization to further enhance the performance of kesterite‐based thin film solar cells as well as other Se‐ or S‐containing solar cells.