Role of an external electric field on hybrid halide perovskite CH3NH3PbI3 band gaps

Abstract

The organic-inorganic perovskite CH₃NH₃PbI₃ has attracted much attention due to their power conversion efficiency as a potential photovoltaic material, but the role of an external electric field has not been well understood. Based on first-principles calculations, the effects of an external electric field (E) applied along the [111] direction of the orthorhombic perovskite, CH₃NH₃PbI₃, on its electronic structure and optical properties are investigated. Our results indicate that the electric field strength affects the band gap (E_g) of CH₃NH₃PbI₃ (MAPbI₃, MA = CH₃NH₃). The energy difference between the two peaks closest to the Fermi level in the density of states diagram decreases with increasing applied electric field strength along the [111] direction, indicating that the covalent character increases between A-sites cations and I-sites anions. Both the cell volume and the final energy show the same increasing trend. The absorption peaks move toward the visible-frequency range, with the optimal band gap of 1.1-1.45 eV and E = 0.04-0.06 eV/Å/e. In particular, the non-linear change of the second-order Stark effect causes a non-linear change in the band gap.