Defect properties of the two-dimensional (CH3NH3)2Pb(SCN)2I2 perovskite: a density-functional theory study

Abstract

Recently, solar cells based on 2D (CH₃NH₃)₂Pb(SCN)₂I₂ perovskite have realized a power conversion efficiency of 3.23%. In this work, we study the defect properties of (CH₃NH₃)₂Pb(SCN)₂I₂ through density-functional theory calculations. It is found that the lower crystal structure dimensionality of (CH₃NH₃)₂Pb(SCN)₂I₂ makes the valence band maximum lower and the conduction band minimum higher as compared to its 3D CH₃NH₃PbI₃ perovskite counterpart, resulting in relatively deeper defect transition levels. Our calculated defect formation energies suggest that if the 2D (CH₃NH₃)₂Pb(SCN)₂I₂ perovskite absorbers are synthesized under Pb-poor and I-rich conditions, the dominant defects should be Pb vacancies, which create shallow levels. The resultant perovskite films are expected to exhibit p-type conductivity with a relatively long carrier lifetime.