In Situ PL Probes the Effect of 2D SnSe Nanosheets on the Crystallization Process of CsPbI₂Br Perovskite Solar Cells

Reducing defects in the active layer is important for improving the crystalline quality of all-inorganic perovskite solar cells (PSCs). Exploring novel additives is one of the most promising approaches to minimize active layer defects. In this work, two-dimensional (2D) SnSe nanosheets with excellent optoelectronic properties are prepared using an ultrasonic exfoliation method. The prepared 2D SnSe nanosheets are introduced into a CsPbI₂Br precursor, which reduces the defect formation at grain boundaries and enhances the crystallinity of CsPbI₂Br perovskites. We use the in situ photoluminescence (PL) technique to investigate the role of 2D materials in the crystallization process. The results show that SnSe nanosheets primarily shorten the grain boundary merging time and reduce the defect generation during the grain boundary merging stage, thereby regulating the crystallization of perovskite. In addition, SnSe nanosheets passivate uncoordinated Pb atoms at grain boundaries by Se atoms, further reducing the defect density in perovskite. As a result, PSCs exhibit a higher power conversion efficiency (PCE) of 14.24% and a <i>V</i>_oc of 1.22 V. This study highlights the role of 2D materials in enhancing the crystalline quality and PCE of PSCs.