Long Carrier Lifetimes in PbI₂-Rich Perovskites Rationalized by Ab Initio Nonadiabatic Molecular Dynamics

Abstract

Hybrid organic–inorganic perovskites have attracted considerable interest due to their impressive performance in solar energy applications. Many experiments show that a slight excess of PbI2 significantly enhances the properties of the most studied CH3NH3PbI3 compound. We use real-time time-dependent density functional theory and nonadiabatic molecular dynamics to demonstrate that the effect arises due to decreased electron–phonon interactions responsible for nonradiative charge recombination. The fast organic CH3NH3 + (MA) cations, present on surfaces of stochiometric and MAI-rich perovskites, are particularly mobile and introduce high-frequency phonons and strong electric fields that couple to the charge carriers and create large nonadiabatic coupling. Excess PbI2 decreases MA surface coverage, reduces the nonadiabatic coupling by up to an order of magnitude, and extends the charge carrier lifetime. Generally, charges in perovskites are long-lived because the nonadiabatic coupling is very small, less than 1 meV, and quantum coherence formed during charge recombination is short, less than 10 fs. Our results rationalize why decreasing the concentration of the organic cations on perovskite surfaces can suppress nonradiative charge carrier recombination and improve material performance.

Structural rigidity accelerates quantum decoherence and extends carrier lifetime in porphyrin nanoballs: a time domain atomistic simulation

“…41 DISH has been used effectively for studying the charge recombination phenomena in various systems. [42][43][44] A detailed theoretical approach can be found elsewhere. 42,[45][46][47][48][49] All quantum-mechanical calculations including geometry optimization and electronic structure are carried out by the SCC-DFTB method as implemented in the DFTB+ code.…”

First-Principles Modeling of Defects in Lead Halide Perovskites: Best Practices and Open Issues

“…Several computational studies have been carried on native defects in perovskites, mainly employing Density Functional Theory (DFT). 12,13,[54][55][56][57][58][59][60][61][62][63][64][65][67][68][69][70][71][72][73][74][75][76][77][78][79][80] Yin et al performed calculations on the cubic phase of MAPbI 3 reporting that only shallow defect states exist in this phase, with a predominance of lead vacancies (V Pb ) and methylammonium interstitial (MA i ) defects. 12 Buin et al…”

Ligand‐Modulated Excess PbI2 Nanosheets for Highly Efficient and Stable Perovskite Solar Cells

“…[ 16,19–22 ] The benefits of excess PbI 2 in perovskite films are mainly assigned to its passivation effect, leading to longer carrier lifetime and reduced halide vacancy concentration. [ 19,23–25 ] However, excess PbI 2 is a double‐edged sword. [ 24 ] It also results in the inhibited charge transport and accelerated degradation of perovskite layer likely due to the photodecomposition of PbI 2 and the increasing ionic movement.…”