Finite-temperature optoelectronic properties of halide perovskites from first-principles

Excitons, correlated electron-hole pairs, play a central role in the photophysics of semiconductors and insulators. The exciton binding energy, and hence exciton formation and dissociation, is governed by the Coulomb interaction modulated by the dielectric properties of the material. State-of-the-art ab initio methods such as the GW and Bethe–Salpeter equation (GW-BSE) framework typically only include the electronic contribution to dielectric screening but neglect ionic contributions and finite temperature effects. Recent work demonstrated that lattice screening effects contribute significantly to exciton binding energies but neglected other finite temperature effects. In this contribution, we combine GW-BSE and density functional perturbation theory with large-scale molecular dynamics simulations to study the temperature dependence of band gaps and exciton binding energies of representative halide perovskites. Our calculations are in very good agreement with experiment and allow us to disentangle various contributions to these optoelectronic properties.