Inorganic-Cation Pseudohalide 2D Cs2 Pb(SCN)2 Br2 Perovskite Single Crystal.

Abstract

Most of the reported 2D Ruddlesden-Popper (RP) lead halide perovskites with the general formula of An +1 Bn X3 n +1 (n= 1, 2, …) comprise layered perovskites separated by A-site-substituted organic spacers. To date, only a small number of X-site-substituted RP perovskites have been reported. Herein, the first inorganic-cation pseudohalide 2D phase perovskite single crystal, Cs2 Pb(SCN)2 Br2 , is reported. It is synthesized by the antisolvent vapor-assisted crystallization (AVC) method at room temperature. It exhibits a standard single-layer (n= 1) Ruddlesden-Popper structure described in space group of Pmmn (#59) and has a small separation (d= 1.69 Å) between the perovskite layers. The SCN- anions are found to bend the 2D Pb(SCN)2 Br2 framework slightly into a kite-shaped octahedron, limiting the formation of a quasi-2D perovskite structure (n> 1).This 2D single crystal exhibits a reversible first-order phase transformation to 3D CsPbBr3 (Pm3m #221) at 450 K. It has a low exciton binding energy of 160 meV-one of the lowest for 2D perovskites (n= 1). A Cs2 Pb(SCN)2 Br2 -single-crystal photodetector is demonstrated with respectable responsivity of 8.46mA W-1 and detectivity of ≈1.2 × 1010 Jones at a low bias voltage of 0.5V.