First-principles calculation study of electronic structures of alkali metals (Li, K, Na and Rb)-incorporated formamidinium lead halide perovskite compounds

Electronic structures of alkali metals (Li, Na, K or Rb)-incorporated formamidinium lead halide perovskite compounds were investigated by first-principles calculation. The conduction band were supplied with electrons from energy levels at 2s, 3s, 4s and 5s orbital of alkali metal to energy levels at 6p orbital of Pb atom in the perovskite crystal. Deviation of charge distribution in the perovskite crystal promoted the photo-induced charge generation, electron correlation and electron-lattice interaction as phonon effectiveness. The chemical shifts of I-127-NMR in the perovskite crystal were originated in a slight perturbation of the coordination structure with nuclear quadruple interaction based on the electric field gradient. The slight incorporation of alkali metal near the ligand structure decreased the enthalpy with the Gibbs free-energy by contribution of the entropy due to the P-I stretching vibration.