2021 Adv. Mater.: How does 2D Cs2Pb(SCN)2Br2 perovskite single crystal achieve the lowest value of 160 mev?
Advanced Materials (IF 30.849) published a study by Anita WY Ho-Baillie from the University of Sydney in Australia and Chu-Chen Chueh from Taiwan University in December 2021. They reported the first inorganic cation pseudohalide two-dimensional Cs2Pb(SCN)2Br2 perovskite single crystal. Various layered lead halide perovskites based on Ruddlesden-Popper (RP) structure have been developed, with the general formula An+1BnX3n+1 (n = 1, 2, …). Especially for the RP-type perovskites substituted at the A position, most of them are composed of layered perovskites and organic spacers with long insulating chains. At present, there are only a few two-dimensional (2D) RP type perovskite reported.
In this study, the research team reported the first inorganic cation pseudohalide two-dimensional phase perovskite single crystal Cs2Pb(SCN)2Br2. Synthesized by anti-solvent vapor assisted crystallization (AVC) method, Cs2Pb(SCN)2Br2 in the Pmmn (#59) space group exhibited a standard single-layer (n = 1) Ruddlesden-Popper structure. Besides, the separation between the perovskite sheets was small (d = 1.69 Å). By Enlitech’s PD-RS Photodetector/Photodiode/Photoreciever Frequency Response Tester, the rise time and decay time of the laser light were both less than 5 ns under 405 nm (2.72 W/cm2) laser light. And the data acquisition device amplified and collected the photo-generated current under the bias voltage with a time resolution of 50 μs.
The research team found that the SCN-anion slightly bended the 2D Pb(SCN)2Br2 framework into a kite-shaped octahedron, while limiting the formation of a quasi-2D perovskite structure (n> 1). Surprisingly, this 2D single crystal exhibited the reversible first-order phase transition of 3D CsPbBr3 (Pm3m #221) at 450 K. Detected by a photoluminescence (PL) instrument, Cs2Pb(SCN)2Br2 single crystal exhibited an exciton binding energy of 160 meV. This value is one of the lowest values reported for 2D perovskites (n = 1) and is equivalent to the one of a quasi-2D RP phase perovskite. The results of the study proved that under a low bias voltage of 0.5 V, the Cs2Pb(SCN)2Br2 single crystal photodetector had a responsivity of 8.46 mA W-1 and a detection rate of ~1.2 x 1010 Jones.
Performance comparison of 2D perovskite single crystal photodetector.
Recommended Instruments: PD-RS Photodetector/Photodiode/Photoreciever Frequency Response Tester