Lead Replacement in CH3NH3PbI3 Perovskites

Superior photovoltaic performance in organic-inorganic hybrid perovskite is based on the unique properties of each moiety contined within it. Identifying the role of metal atoms in the perovskite is of great importance to explore the low-toxicity lead-free perovskite solar cells. By using the first-principle calculations, four types of AMX(3) (A = CH3NH3, M = Pb, Sn, Ge, Sr, X = I) perovskite materials are investigated and an attempt is made to understand the structural and electronic influences of the metal atoms on the properties of perovskites. Then, the solutions to the replacement of Pb are discussed. It is found that for the small radius metal atoms as compared with Pb, the strong geometry distortion will result in a less p-p electron transition and larger carrier effective mass. The outer ns(2) electrons of the metal ions play critical roles on the modulation of the optical and electronic properties for perovskite materials. These findings suggest that the solutions to the Pb replacement might be metal or metallic clusters that have effective ionic radius and outer ns(2) electrons configuration on the metal ions with low ionization energy similar to Pb2+. Based on this, lead-free perovskite solar cells are expected to be realized in the near future.