Ferroelectric polarization driven optical absorption and charge carrier transport in CH3NH3PbI3/TiO2-based photovoltaic cells

Time-dependent density-functional theory(TD-DFT) calculations show that photogenerated electrons accumulate at the interface of CH3NH3PbI3/TiO2. Electrons transport from CH3NH3PbI3 side to TiO2 side, and the recombination of charge carriers is significantly reduced in this heterostructure. This can unambiguously explain why the power conversion efficiency and the open-circuit voltage are so high in the mesoporous TiO2 with an ultrathin layer of the hybrid halide perovskites. The calculated absorption spectrum of CH3NH3PbI3 agrees well with the experimental measurements. Our TD-DFT calculations confirm the connection between the ferroelectric polarization and the optical absorption. The polarization is caused by the combination of stereochemical activity of the lone pair of Pb-6s2 and the distortions of the organic moieties. Ti-3d states play crucial role in the formation of electron-hole pairs and make TiO2 as an electron transport material.