Methylammonium lead iodide perovskite (CH3NH3PbI3) plays an important role in light absorption and carrier transport in efficient organic-inorganic perovskite solar cells. In this Letter, we report the first theoretical estimation of effective masses of photocarriers in CH3NH3PbI3. Effective masses of photogenerated electrons and holes were estimated to be me* = 0.23m0 and mh* = 0.29m0, respectively, including spin-orbit coupling effects. This result is consistent with the long-range ambipolar transport property and with the larger diffusion constant for electrons compared with that for holes in the perovskite, which enable efficient photovoltaic conversion.

We report on an analysis of hot-carrier lifetimes from electron-phonon interaction in lead iodide perovskites using first-principles calculations. Our calculations show that the holes in CsPbI3 have very long lifetimes in the valence band region situated 0.6 eV below the top of the valence band. On the other hand, no long lifetime is predicted in PbI3(-). These different results reflect the different electronic density of states (DOSs) in the valence bands, that is, a small DOS for the former structure while a sharp DOS peak for the latter structure. We propose a reduction of the relaxation paths in the small valence DOS as being the origin of the slow hot-hole cooling. Analyzing the generalized Eliashberg functions, we predict that different perovskite A-site cations do not have an impact on the carrier decay mechanism. The similarity between the DOS structures of CsPbI3 and CH3NH3PbI3 enables us to extend the description of the decay mechanism of fully inorganic CsPbI3 to its organic-inorganic counterpart, CH3NH3PbI3.

Moving from a general revise of the structural and electronic properties of the 3D methylammoniumtrihalogenoplumbates (MAPbX3, X = Cl, Br, I) class of halide organic–inorganic perovskites, we have focused our attention on the organic cation and studied the role it plays in the electronic/optical features of this class of compounds, paying attention mainly to the iodide compound. We found good agreement with previous experimental works, but at the same time we observed that the bare inorganic network [PbX3]− does not fully take into account the electronic properties of 3D systems. A comparison is performed between the electronic properties of MAPbI3 organic–inorganic perovskite and those of the purely inorganic CsPbI3. Furthermore, we show that hybrid methods applied on top of the spin–orbit calculated structures are not able to open the bandgap sufficiently to reproduce the experimental value, revealing the need of further and more computationally demanding procedures to get improved agreement.

Three-dimensional organic-inorganic lead iodide perovskites are potential photoconductive materials for solar cells. Nowadays, a high power conversion efficiency exceeding 20% can be achieved. However, perovskite solar cells are reported to suffer from a large hysteresis in the current-voltage curves. This may be attributed to the motion of organic cations with a permanent dipole moment in response to the applied electric field. Therefore, in order to suppress the hysteresis, organic cations that have a zero dipole moment and a molecular size well fitted to the lead iodide cavity are required. Using density functional theory calculations, we theoretically studied the thermodynamic stability and electronic properties of lead iodide perovskites with large guanidinium cations having a nearly zero dipole moment, and compared the results with those predicted via the Goldschmidt tolerance factor. The properties of formamidiniumguanidinium (FA 1-x GA x PbI 3 ) intermediate alloys were also investigated.

Methylammonium lead iodide perovskite (CH3NH3PbI3), the most investigated hybrid organic-inorganic halide perovskite, is characterized by a quite low thermal conductivity. The rotational motion of methylammonium cations is considered responsible for phonon transport suppression; however, to date, the specific mechanism of the process has not been clarified. In this study, we elucidate the role of rotations in thermal properties based on molecular dynamics simulations. To do it, we developed an empirical potential for CH3NH3PbI3 by fitting to ab initio calculations and evaluated its thermal conductivity by means of nonequilibrium molecular dynamics. Results are compared with model systems that include different embedded cations, and this comparison shows a dominant suppression effect provided by rotational motions. We also checked the temperature dependence of the vibrational density of states and specified the energy range in which anharmonic couplings occur. By means of phonon dispersion analysis, we were able to fully elucidate the suppression mechanism: the rotations are coupled with translational motions of cations, via which inorganic lattice vibrations are coupled and scatter each other.