Unraveling the role of low-frequency phonon modes in carrier relaxation and regeneration in lead-halide perovskites*

Carrier-phonon scattering, a ubiquitous effect in all condensed matter systems, has been discussed in the halide perovskites in the context of placing an upper limit to the carrier mobility. Using time-resolved terahertz spectroscopy on a formamidinium-based perovskite system, we will show that phonons play a much larger role than thought previously. The combination of phonon emission during carrier relaxation, phonon-assisted exciton dissociation, and free-carrier screening, ensure a large and long-lived carrier population in the material. Our work reveals the delicate interplay among carriers, phonons and excitons, that affect the photo-physical properties of the halide perovskites, that ultimately determines the photovoltaic performance of halide perovskite-based solar cells.