The utility of optoelectronic materials can be greatly reduced by the presence of efficient pathways for nonradiative recombination (NRR). Lead halide perovskites have garnered much attention in recent years as materials for solar energy conversion, because they readily absorb visible light, are easy to synthesize, and have a low propensity for NRR. Here we report a theoretical study of the pathways for NRR in an archetypal lead halide perovskite: CsPbBr 3 . Specifically, we identified a set of conical intersection (CIs) in both a molecule-sized cluster model (Cs 4 PbBr 6 ) and nanoparticle model (Cs 12 Pb 4 Br 20 ) of the CsPbBr 3 surface. The energies of the minimal energy CIs, corrected for both dynamical electron correlation and spin-orbit coupling, are well above the bulk band gap of CsPbBr 3 , suggesting that these intersections do not provide efficient pathways for NRR in this material. Analysis of the electronic structure at these intersections suggests that the ionic nature of the bonds in CsPbBr 3 may play a role in the high energy of these CIs. The lowest-energy intersections all involve charge transfer over long distances, whether it be across a dissociated bond or between neighboring unit cells.
Bibliographical noteFunding Information:
We are grateful for the financial support of the NSF through Grant No. CHE-1565634 and Michigan State Univ. through a Strategic Partnership Grant. We are also grateful for a generous allocation of supercomputer time from the Extreme Science and Engineering Discovery Environment, which is supported by the NSF under Grant No. ACI-1548562 (allocation CHE-140101).
© 2019 American Chemical Society.