Theoretical and Experimental Research on the Bulk Photovoltaic Effect in Hybrid Organic-Inorganic Perovskites CH3NH3PbI2X (X = Cl, Br, I)

Perovskite solar cells based on three hybrid organic-inorganic perovskite CH3NH3PbI2X (X = I, Cl, Br) materials were fabricated, and the photoelectric conversion efficiency of CH3NH3PbI2Cl was found to be the highest among them. The band structures, the density of states and light absorption properties of these materials were investigated by the Density Functional Theory (DFT) calculations. By geometry optimization of the tetragonal phase structure, we have found that C-N bonds are distributed in a parall way in [CH3NH3](+). Chlorine (Cl) atom occupy the apical positions in CH3NH3PbI2Cl material, while bromine (Br) and iodine (I) atoms occupy both apical and equatorial positions in CH3NH3PbI2Br and CH3NH3PbI3. In addition, it has been found that the stability of CH3NH3PbI2Cl is superior to that of CH3NH3PbI2Br and CH3NH3PbI3. By calculation of electron effective mass, we further found that the carrier mobility of the CH3NH3PbI2Cl is higher than that of the CH3NH3PbI3 and CH3NH3PbI2Br. With the help of both experimental and theoretical methods, we have explained why Cl-mixed CH3NH3PbI3 afforded the best highest conversion efficiency in CH3NH3Pb2X (X = Cl, Br, I) materials. These results provide theoretical guidance for developing new perovskite materials for future photovoltaics.