Organic-inorganic hybrid halide perovskites are a promising class of materials for photovoltaic application with reported power efficiencies over ∼22%. However, not much is known about the influence of the organic dipole rotation and phase transitions on charge carrier dynamics. Here, we report substantial changes in mobility and lifetime of charge carriers in CH3NH3PbI3 after the low-temperature tetragonal (β) to orthorhombic (γ) phase transition. By using microwave conductivity measurements, we observed that the mobility and lifetime of ionized charge carriers increase as the temperature decreases and a sudden increment is seen after the β-γ phase transition. For CH3NH3PbI3, the mobility and the half-lifetime increase by a factor of 3-6 compared with the values before the β-γ phase transition. We attribute the considerable change in the dynamics at low temperature to the decrease of the inherent dynamic disorder of the organic cation (CH3NH3 +) inside the perovskite crystal structure.@en

We present ab initio calculations (DFT and SOC-G0W0) of the optoelectronic properties of different hybrid-halide perovskites, namely X-PbI3 (X = methylamonimum, formamidinium, guanidinium, hydrazinium, and hydroxylammonium). These calculations shed new light on how the substitution of different organic cations in the material influences its optoelectronic properties. Our simulations show a significant modification of the lattice parameter and band gap of the material upon cation substitution. These modifications are not only due to steric effects but also due to electrostatic interactions between the organic and inorganic parts of the material. In addition to this, we demonstrate how the relative orientations of neighboring cations in the material modify the local electrostatic potential of the system and its fundamental band gap. This change in the band gap is accompanied by the formation of localized and spatially separated electronic states. These localized states modify the carrier mobility in the materials and can be a reason for the formation and recombination of the charge carriers in these very promising materials.@en