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

The organic-inorganic perovskite CHNHPbI 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, CHNHPbI, on its electronic structure and optical properties are investigated. Our results indicate that the electric field strength affects the band gap (E) of CHNHPbI (MAPbI, MA = CHNH). 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.