Dual effect of NH4F additive in the hydrothermal deposition of antimony selenosulfide thin film for high-performance solar cells

Hydrothermal deposition of antimony selenosulfide (Sb-2(S,Se-3)) has enabled solar cell applications to surpass the 10% efficiency threshold. This deposition process involves the reaction of three precursor materials: Sb, S, and Se. However, this process generates an unfavourable gradient of Se and S anions in the Sb-2(S,Se)(3) film, which limits further efficiency improvements. Herein, we demonstrate how NH4F can be used as an additive to regulate the band gradient of the Sb-2(S,Se)(3) and modify the surface of the CdS electron-transporting layer. On the one hand, NH4F inhibits the decomposition of Na2S2O3 and selenourea, which optimizes the deposition process and allows for adjustment of the Se/S ratio and their distribution in the Sb-2(S,Se)(3) film. On the other hand, hydrolysis of NH4F induces dissolution and redeposition of CdS, thereby effectively improving the morphology and crystallinity of the CdS substrate. Finally, the dual effect of NH4F enables improved surface morphology and energy alignment of the Sb-2(S,Se)(3) film, thus yielding a maximum efficiency of 10.28%, a 12% improvement over the control device. This study demonstrates an effective strategy for simultaneously modifying a sulfide-based substrate and regulating the element distribution during the deposition of a metal chalcogenide film for optoelectronic device applications.