Breathing bands due to molecular order in CH3NH3PbI3

Abstract

CH 3 NH 3 PbI 3 perovskite is nowadays amongst the most promising photovoltaic materials for energy conversion. We have studied by ab-initio calculations, using several levels of approximation -namely density functional theory including spin-orbit coupling and quasi-particle corrections by means of the GW method, as well as pseudopotential self-interaction corrections-, the role of the methylammonium orientation on the electronic structure of this perovskite. We have considered many molecular arrangements within 2 × 2 × 2 supercells, showing that the relative orientation of the organic molecules is responsible for a huge band gap variation up to 2 eV. The band gap sizes are related to distortions of the PbI 3 cage, which are in turn due to electrostatic interactions between this inorganic frame and the molecules. The strong dependence of the band gap on the mutual molecular orientation is confirmed at all levels of approximations.Our results suggest then that the coupling between the molecular motion and the interactions of the molecules with the inorganic cage could help to explain the widening of the absorption spectrum of CH 3 NH 3 PbI 3 perovskite, consistent with the observed white spectrum.

Tuning the Optical Properties of Already Crystalized Hybrid Perovskite

“…In addition, an overlap of two PL peaks is observed for pure FABr and 25/75, which indicates the formation of a secondary phase and a nonuniform halide distribution in the perovskite lattice. These features of PL, especially the peak broadening in the Br‐rich samples, are consistent with the negative formation energies for all types of the Br distributions and the fact that each Br pattern is associated with a different energy gap …”

“…Interestingly, the organic cations (FA) seem to adjust their orientations to the pattern of the Br distribution, i.e., the clustered cases (C‐type) possess very well‐ordered molecular phase. This fact, in turn, might affect the speed of molecular rotations and the bandgaps breathing …”

Electronic structure of Li+@C60 adsorbed on methyl-ammonium lead iodide perovskite CH3NH3PbI3 surfaces

“…Many studies show that the MA orientation play important role in governing the stability and electronic structures of MAPbI 3 . 7,42,[45][46][47][48] The orientation of MA molecule has a significant effect on the charge mobility, 46 the bandgap change 47 and photo-energy conversion efficiencies. 7,48 Neutron scattering measurements suggested the formation of either antiferroelectric or ferroelectric domains in these perovskites based on the ordered orientation of MA cations.…”

Halide Pb-Free Double–Perovskites: Ternary vs. Quaternary Stoichiometry

“…The great advantage of a ternary perovskite is the enhanced dispersion associated with the strong coupling between B-site and halide states, a feature that does not characterize the quaternary stoichiometry (see, among the others, [46] for the organic-inorganic case). This is further testified to by the calculation of the effective masses of the compound that show values comparable to the best PV performing perovskite; i.e., MAPbI 3 [110,111]. It is, anyway, the inclusion of local-field and excitonic effects, solving the Bethe-Salpeter equation [108], that provides the most interesting features of this compound.…”