In\nSitu PL Probes the Effect of 2D SnSe Nanosheets\non the Crystallization Process of CsPbI<sub>2</sub>Br Perovskite Solar\nCells

Reducing defects in the active layer\nis important for improving\nthe crystalline quality of all-inorganic perovskite solar cells (PSCs).\nExploring novel additives is one of the most promising approaches\nto minimize active layer defects. In this work, two-dimensional (2D)\nSnSe nanosheets with excellent optoelectronic properties are prepared\nusing an ultrasonic exfoliation method. The prepared 2D SnSe nanosheets\nare introduced into a CsPbI<sub>2</sub>Br precursor, which reduces\nthe defect formation at grain boundaries and enhances the crystallinity\nof CsPbI<sub>2</sub>Br perovskites. We use the in situ photoluminescence\n(PL) technique to investigate the role of 2D materials in the crystallization\nprocess. The results show that SnSe nanosheets primarily shorten the\ngrain boundary merging time and reduce the defect generation during\nthe grain boundary merging stage, thereby regulating the crystallization\nof perovskite. In addition, SnSe nanosheets passivate uncoordinated\nPb atoms at grain boundaries by Se atoms, further reducing the defect\ndensity in perovskite. As a result, PSCs exhibit a higher power conversion\nefficiency (PCE) of 14.24% and a <i>V</i><sub>oc</sub> of\n1.22 V. This study highlights the role of 2D materials in enhancing\nthe crystalline quality and PCE of PSCs.