Structural characterizations on the degradation of 2D organic-inorganic hybrid perovskites and its enlightenment to improved stability.

Despite the demonstrated high-efficiency of solar cells and light-emitting devices based on two-dimensional (2D) perovskites, intrinsic stability of the 2D perovskites is yet far from satisfactory. In this work, we find the 2D (BA) 2 PbI 4 perovskite crystals rapidly degrade in the ambient conditions and the photoluminescence (PL) nearly completely quenches in 6 d. Moreover, the PL shoulder band due to defects and absorption band of PbI 2 gradually rise during degradation, suggesting the precipitation of PbI 2 . Besides, rod structures are observed in the degraded crystals, which are attributed to the formation of one-dimensional (1D) (BA) 3 PbI 5 perovskites. And the degradation can be largely retarded by decreasing the humidity during storage. Therefore, a chemical reaction for the degradation of (BA) 2 PbI 4 is proposed, revealing the interactions between water molecules and undercoordinated defects are very critical for understanding the degradation. Enlightened by these findings, dimethyl itaconate (DI) treatment is developed to passivate the defects and block the intrusion of moisture to improve the stability of the (BA) 2 PbI 4 . After storage in the ambient environment for 16 d, the DI treated (BA) 2 PbI 4 only shows a slight surface degradation without formation of any nanorod-like structures, and the PL intensity retains about 70%. Therefore, our systematic study provides a comprehensive understanding on the degradation dynamics of 2D perovskites, which will promote future development of intrinsically stable 2D perovskites.