Qualifying composition dependent p and n self-doping in CH3NH3PbI3

We report the observation of self-doping in perovskite. CH3NH3PbI3 was found to be either n- or p-doped by changing the ratio of methylammonium halide (MAI) and lead iodine (PbI2) which are the two precursors for perovskite formation. MAI-rich and PbI2-rich perovskite films are p and n self-doped, respectively. Thermal annealing can convert the p-type perovskite to n-type by removing MAI. The carrier concentration varied as much as six orders of magnitude. A clear correlation between doping level and device performance was also observed.