Influences of the orientations of CH3NH3 molecules on physical properties of organo-inorganic hybrid perovskite CH3NH3PbI3

Abstract The organo-inorganic hybrid perovskite CH3NH3PbI3 has a great potential as the photovoltaic material due to its high energy conversion efficiency. In this work, electronic structures, mechanical and optical properties of CH3NH3PbI3 in cubic, tetragonal and orthorhombic structures are systematically investigated using density functional theory, in which unitary and arbitrary CH3NH3 molecular configurations in cubic and tetragonal phases are considered. Among them, the orthorhombic phase possesses the largest band gap and elastic moduli. For the tetragonal phase, the CH3NH3PbI3 with the arbitrary CH3NH3 molecular orientation owns higher Young's/shear moduli and lower band gap than that with the unitary orientation, while the opposite trend is observed for the cubic phase. Moreover, the orthorhombic and tetragonal phases possess similar peak energy levels of the dielectric function, absorption coefficients and reflectivity. In the case of the cubic phases, these peaks move towards the low energy direction as a result of their decreased band gaps. Meanwhile, optical absorption peaks of materials with unitary molecular configurations locate at higher energy levels than those with arbitrary orientations. These results are expected to arouse the attention on the effect of crystal structure and the CH3NH3 molecular orientation on the properties and guide the future performance optimization of CH3NH3PbI3 through structural design.