Study of strain effects on electronic and optical properties of CH3NH3PbX3 (X= Cl, Br, I) perovskites

Abstract

Nowadays, solar cells based on organic-inorganic halide perovskites are among the most exciting topics in the field of renewable energies. In this work, through studying the cubic phase of CH3NH3PbX3 (X = Cl, Br, I) perovskites, the effect of strain (tensional and compressive) on electronic and optical properties of these materials have been investigated by density functional theory (DFT) and PBEsol, SOC and HSE06 approximations. PBEsol calculations were in good agreement with the experimental results. The results were demonstrated that tensional strain causes an increase of the band gap in these structures and this might be the origin of the experimentally beheld band gap variations. This tensional strain which could be equal to the thermal expansion of the material under sunlight or any mismatch with the sublayer or other reasons will change its properties and decrease its performance. In CH3NH3PbI3 and CH3NH3PbBr3 the band gap gets wider due to a decrease in valence band maximum (VBM) under applying strain. In contrast, the band gap widening of CH3NH3PbCl3 caused by increasing in conduction band minimum (CBM). Moreover, the results of optical properties show that because of this dimensional expansion, the optical adsorption edges of CH3NH3PbX3 have a blue shift and moves toward higher energies. All studied structures have a strong absorption coefficient (in order of 105 cm−1) in the visible region.