Room‐Temperature Surface Sulfurization for High‐Performance Kesterite CZTSe Solar Cells

The interfaces are very important for kesterite‐structured solar cells. In this study, a facile room temperature chemical sulfurization process is developed to modify the surface of the CZTSe films, which can prevent the decomposition of kesterite film at high temperature during the traditional sulfurization process and thus introducing the deep defects in the absorber layer. It is found that the (NH4)2S vapor sulfurizes the surfaces of the CZTSe thin films previously etched by ammonia. Consequently, the surface defects are passivated by the incorporated sulfur, and the interfacial band alignment is improved at the junction. The open circuit voltage (VOC) of the solar cell device is improved from 364 mV to 406 mV, with the cell efficiency increased to 9.04% when the (NH4)2S vapor treatment time is optimized at 25 min. This study affords a new perspective for enhancing the performance of kesterite‐based thin film solar cells using a facile surface sulfurization approach. The CZTSe surface is sulfurized at room temperature. After etching in concentrated ammonia solution followed by (NH4)2S vapor modification, the surface defects are passivated and the band alignment at the CZTSe/CdS interface is modified. The efficiency of the solar cell is increased to 9.04% with the (NH4)2S vapor treatment for 25 min.