Layered Perovskite (CH₃NH₃)₂Pb(SCN)₂I₂ Single Crystals: Phase Transition and Moisture Stability

To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN–) into CH3NH3PbI3 (MAPbI3) to solve these problems. Here, we report the bulk growth of layered perovskite MA2Pb(SCN)2I2 single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA2Pb(SCN)2I2 single crystals. More importantly, the phase transition and stability of MA2Pb(SCN)2I2 are systematically demonstrated. MA2Pb(SCN)2I2 undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn (no. 59) to the space group Pmn21 (no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA2Pb(SCN)2I2 single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA2Pb(SCN)2I2 is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.