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

Recently, solar cells based on 2D (CH3NH3)(2)Pb(SCN)(2)I-2 perovskite have realized a power conversion efficiency of 3.23%. In this work, we study the defect properties of (CH3NH3)(2)Pb(SCN)(2)I-2 through density-functional theory calculations. It is found that the lower crystal structure dimensionality of (CH3NH3)(2)Pb(SCN)(2)I-2 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)(2)Pb(SCN)(2)I-2 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.