Unipolar self-doping behavior in perovskite CH3NH3PbBr3

Recent theoretical and experimental reports have shown that the perovskite CH3NH3PbI3 exhibits unique ambipolar self-doping properties. Here, we show by density-functional theory calculation that its sister perovskite, CH3NH3PbBr3, exhibits a unipolar self-doping behavior—CH3NH3PbBr3 presents only good p-type conductivity under thermal equilibrium growth conditions. We further show that despite a large bandgap of 2.2 eV, all dominant defects in CH3NH3PbBr3 create shallow levels, which partially explains the ultra-high open-circuit voltages achieved by CH3NH3PbBr3-based thin-film solar cells. Our results suggest that the perovskite CH3NH3PbBr3 can be both an excellent solar cell absorber and a promising low-cost hole-transport material for lead halide perovskite solar cells.