Tuning the Polaronic Properties of Hybrid Organic-Inorganic Perovskites CH₃NH₃PbI₃ by Mixing Cation

Formation of polaron quasiparticles has been proved to be very important for describing the charge carrier behavior in hybrid organic-inorganic perovskites. Hybrid organic-inorganic perovskite materials with mixed cations have made tremendous achievement in the enhancement of power conversion efficiency and improved perovskite stability. Inspired by this point, here we report the results from computationally intensive studies of formation energies, electronic structure, charge density and tunable polaronic properties via mixing cations by Cs and FA ions in MAPbI₃ (MA = CH₃NH₃) based on periodic boundary conditions and isolated structures. Our results show that the introduction of an individual cesium (Cs) substitution enhance the ambient stability, in contrast to the decreased stability by doping one formamidinium (FA = HC(NH₂)₂) cation. Importantly, the cations-alloying significantly reduces the polaron binding energies both for holes and electrons, about 2-times decrease compared to pure MAPbI₃. Such reduced reorganization energies suggest the appearance of enlarged polarons in HOP materials with delocalized spin density distribution and finally attenuate electron-phonon coupling guaranteeing efficient charge separation.