Unveiling the Nature of Light-Triggered Hole Traps in Lead Halide Perovskites: A Study with Time-Dependent Density Functional Theory.

Structural variations of lead halide perovskites (LHPs) upon light illumination play an important role in their photovoltaic applications. However, density functional theory (DFT)-based simulations have often been performed to unveil the nature of defects in LHPs without light illumination. So far, the nature of traps in LHPs triggered by the light remains largely unexplored. In this work, hole traps induced by the halogen interstitial in LHPs are studied by combining DFT and time-dependent DFT approaches, the latter of which treats electron-hole and electron-nuclei interactions on the same footing. Both a semilocal exchange functional and hybrid functional are adopted to relax the ground-state and excited-state geometries followed by the calculations of energy levels of hole traps. The effect of the self-interaction corrections on the light-triggered geometric deformation and the electronic structure of hole traps is analyzed. Relaxation energies that correspond to the light-triggered geometric deformation are also calculated with different functionals. The relationship between the hole traps and light-triggered geometric variations are then explored.