Anti-correlation between Band gap and Carrier Lifetime in Lead Halide Perovskites under Compression Rationalized by Ab Initio Quantum Dynamics
Wei Li, Zhi Chen, Jianfeng Tang, Oleg V. Prezhdo
Abstract
Lead halide perovskites have revolutionized the solar cell community. Further optimization of perovskite-based optoelectronic devices requires fundamental understanding of their structure–property relationships. Recent experiments indicate that MAPbI3 and other lead halide perovskites exhibit an unusual pressure dependence of photophysical properties. Typically, decreased band gaps are associated with shorter excited state lifetimes; however, perovskites show the opposite trend. Moreover, the narrower band gap and longer carrier lifetime achieved simultaneously form a favorable combination for solar energy utilization. We rationalize the surprising observation using ab initio nonadiabatic molecular dynamics. Compression of the inorganic lattice enhances the antibonding interaction between the Pb-s and I-p orbitals, raising the valence band maximum and decreasing the band gap. Pressure-induced destabilization of the lattice enhances fluctuations of the Pb and I atoms. The induced disorder localizes electrons and holes, decreasing their overlap. As a result, loss of coherence during the nonradiative relaxation is accelerated, and the relaxation is slowed down. This time-domain decoherence effect is equivalent to the reduction of the Franck–Condon factor in the energy domain, taking place because of a stronger response of the destabilized Pb–I lattice to photoexcitation. The detailed atomistic understanding of the structure–property relationships of lead halide perovskites paves the way for further improvement of perovskite-based optoelectronic devices.