First Principle Polaron Modeling in Hybrid Perovskites Using the GGA+U Method*

Lead halide hybrid perovskites (HPs) are the benchmark, state-of-the-art materials in third generation perovskite solar cells, achieving a power conversion efficiency of over 22%.  Yet, the underlying photo-physical properties of HPs are still under debate. Here we use density functional theory within the generalized gradient approximation with a Hubbard correction (GGA+U) to study structural properties, band structures, and charge carrier dynamics in HPs. Our preliminary DFT+U simulations reveal the formation of hole polarons in HPs with different halides, which have profound implications on device operation and stability. Moreover, we argue that polaron induced loss of inversion symmetry and enhanced Rashba splitting might be responsible for our recent experimentally observed room-temperature ultrafast photocurrent and free-space terahertz emission generation from unbiased CH₃NH₃PbI­₃ HPs. Polarization dependence of the observed photoresponse is consistent with the Bulk Photovoltaic Effect, which may enable next generation perovskite solar cells with efficiency above the Shockley–Queisser limit.