Exploring electronic and optical properties of CH3NH3GeI3 perovskite: Insights from the first principles

The three phases for MAGeI(3) in different temperatures play an important role in hybrid organic-inorganic perovskites solar cells. Up to now, their intrinsic nature still lacks systematic study. In this work, we established the crystal structures of MAGeI(3) (MA(+) = CH3NFT3+) with orthorhombic, tetragonal and cubic phases. The electronic and optical properties of MAGeI(3) with three crystal structures including band gaps, density of states (DOS), absorption spectrum and dielectric function are calculated using the density functional theory (DFT). The calculated results reveal that MAGeI(3) pervoskites show substantial stability, a similar band gap, high carrier mobility and outstanding optical properties compared with MAPbI(3). The electronic properties are computed by GGA+U, demonstrating that the band gaps of MAGeI(3) for orthorhombic, tetragonal and cubic phases are 1.60 eV, 1.58 eV and 1.54 eV, respectively. The calculated results are generally in accord with available reported experimental data. Since the band gaps of MAGeI(3) are appropriate, the absorption region covers almost the entire visible zone. Our work not only uncover screening new materials for solar cells, but also further understand the inherent properties of MAGeI(3). (C) 2017 Elsevier B.V. All rights reserved.