Solution-processed photovoltaics based on lead-halide perovskites have emerged as leading candidates to replace existing photovoltaic technologies because of their high photovoltaic performance (~23 %), and potential for low-cost, high-throughput production. The record efficiencies of perovskite photovoltaics are mainly because of the 1 µm carrier diffusion length (LD) and ~102 ns carrier lifetime exhibited in this class of material. Despite the rapid progress made in lead-halide photovoltaics, a comprehensive understanding of the material’s photophysics and the corresponding role of structural dynamics is still lacking. Such knowledge is critical for the development of design rules about how the electronic properties of perovskites depend on their composition and structure. Using time-resolved infrared (TRIR) spectroscopy, we investigate the structural origins of slow recombination in lead-halide perovskites by probing the vibrational dynamics of the perovskite lattice’s CH3NH3+ cations. We also use TRIR spectroscopy to characterize large polaronic states which slow charge recombination within the perovskite lattice by their spectral signatures in the mid-IR. Our work provides a new framework to understand how fluctuations of the perovskite lattice affect large polaron formation and recombination in this class of material. These findings also suggest that substitution of differently sized ions in halide perovskites can be used to tune the structural flexibility and therefore the self-tapping of charge carriers into large polarons.

Using time-resolved infrared spectroscopy to investigate the structural origins of slow recombination in halide perovskites

2019 Fall National Meeting

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