Origin of enhanced stability in thiocyanate substituted α-FAPbI3 analogues

Abstract

In the past few years, hybrid perovskites have emerged as the most promising photovoltaic materials due to their excellent optoelectronic properties, and easy fabrication methods. However, the long-term stability is still the main obstacle for their commercial applications. Recently, thiocyanate-doped hybrid perovskites have shown enhanced stability and impressive efficiency, but the reason is still unknown. Herein, we discussed the enhanced stability of SCN-substituted pseudocubic FABX3 (B=Pb2+, Sn2+; X=I−, Br−, and Cl−) based on the density functional theory. Through a series of calculations of Bader charge transfer, vacancy formation energies of different kinds of vacancies, decomposition enthalpy, phonon density of states, and ab initio molecular dynamics simulation, we conclude that the incorporation of SCN− can stabilize pseudocubic FABX3, and attribute the enhanced stability mainly to two factors: (1) the strong interaction between Pb2+/Sn2+ and SCN−, as well as the strong hydrogen bonding between FA+ and X−/SCN−, and (2) the structural tilting induced by the incorporation of SCN−. These findings provide alternative method fortuning the poor stability of pseudocubic FABX3, as well as for obtaining high-performance solar cells.