Effects of mixed-valence states of Eu-doped FAPbI3 perovskite crystals studied by first-principles calculation

Abstract

Effects of mixed-valence states of europium (Eu)-incorporated CH(NH₂)₂PbI₃ (FAPbI₃) and CH₃NH₃PbI₃ (MAPbI₃) perovskite crystals on electronic structures were investigated by first-principles calculation. Partial replacements of europium ions into the perovskite crystal influenced the electronic structures and the effective mass related to carrier mobility. In the case of the FAPb(Eu⁺³)I₃ crystal, there was wide distribution of the 5p orbital of iodine near the valence band, and the 3d orbital of the Eu³⁺ ion near the conductive band. The incorporation of Eu³⁺ ion into the crystal slightly caused to increase the effective mass ratio (m_e*/m_e, m_h*/m_e) as compared with those of the FAPbI₃ crystal, provided the wide distribution of 3d, 4f-5p hybrid orbitals near the valence band, and influenced the band dispersion with a decrease of m_e*/m_e and m_h*/m_e, which is expected for improving the carrier mobility. The chemical shifts of ¹²⁷I-NMR of the MAPb(Eu²⁺)I₃ crystal indicated isotropic behavior. The chemical shifts of ¹⁵⁷Eu-NMR and g-tensor depended on the quadrupole interaction based on the electron field gradient and asymmetry parameter in the coordination structure. The electronic correlation based on hybrization of the 3d, 4f-5p orbital in the Eu²⁺-iodine band promoted the carrier itinerary, which was expected to improve the carrier mobility related to the short circuit current density and the conversion efficiency as the photovoltaic performance.