Structural and optical properties of methylammonium lead iodide across the tetragonal to cubic phase transition: implications for perovskite solar cells

Abstract

photovoltaic properties of MAPbI 3 perovskites across the tetragonal to cubic transition, due to structural fluctuations on a sub-picosecond timescale that make the instantaneous electronic energy levels and band-gap of the formally cubic, high temperature structure, to differ only slightly from those of the room temperature stable tetragonal phase. disordered position of the Cl anions 45 and the presence of a Raman signal at 66 cm -1 in the high temperature phase of MAPbCl 3 . 47 From a technological perspective, these results help to explain the lack of an observable abrupt change in photovoltaic device performance above room temperature 23 as would be expected to be observable if the light-harvester undergoes a phase transition. This is also further evidence indicating that ferroelectricity contributions to the optoelectronic properties, as in traditional inorganic materials, 54-57 are negligible, since the ferroelectric polarizability is expected to change dramatically across the transition between two different crystalline structures.On the contrary, this view supports other proposed mechanisms, as the spatial charge localization 50, 58 and/or stable band bending effects at the interfaces and grain boundaries, 59 as the basis of the impressive inherent performance of hybrid lead halide perovskites. ASSOCIATED CONTENT Supplementary InformationExperimental methods; theoretical methods and models; EQE measurements on different MAPbI3 devices; corresponding JV measurements of the devices; EQE of a cell with MAPbI 3-xClx ; comparison between theoretical and experimental radial distribution function of MAPbI 3 perovskite; theoretical fluctuation of the band edges.

Breathing bands due to molecular order in CH3NH3PbI3

“…This effect has been widely described in the literature, so that it will not be described further herein. Here we will just mention that the distortions of the inorganic cage obtained in this work for the most symmetrical configurations agree with the results reported elsewhere [24,28,29,53,54].…”

“…Thus, for direction exhibits large distortions at the sub-picosecond time-scale [53]. This finding, which explains part of the features of the tetragonal-cubic phase transition,…”

Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

“…It was pointed out in a recent study that structural relaxations of the inorganic framework depend sensitively on the assumed direction of the organic molecules, and so does the calculated band gap. 51 Recent neutron scattering experiments 52 and firstprinciple calculations 53 also suggested sizable coupling between the inorganic framework and the organic cation. It should be pointed out that this coupling can be of both static and dynamic in nature, which, when combined with temperature and electron-phonon (el-ph) renormalization effects, can greatly complicate theoretical understanding of the electronic properties of this material.…”

“…Our results also agree with ex-periments that there the change in the measured band gap is negligible (∼ 0.01 eV) across the phase transition temperature. 51,[54][55][56] . Our results on the strong effects of structural distortions on the calculated band gap also agree with previous theoretical works.…”

“…Our results on the strong effects of structural distortions on the calculated band gap also agree with previous theoretical works. 51,58 . Putting all results together, we estimate that the DFT band gap of MAPbI 3 is about 1.68 ± 0.08 eV (Table II).…”