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.