Charge-Phonon Coupling in Tin Halide Perovskites

Tin halide perovskites are promising materials to replace lead-based materials for perovskite optoelectronics, yet their performance is limited by their high self-p-doping. To quantify the impact of p-doping on carrier dynamics, we combine terahertz spectroscopy and density functional theory calculations to investigate the coupling of charge carriers to the lattice in prototypical tin-based perovskites. Doping is shown to influence the charge-phonon interactions significantly. We identify the formation of polarons at doping densities below 10¹⁸ cm^-3, while a Drude-like response is found for photogenerated carriers at higher charge density, confirming that for highly p-doped systems, the terahertz response is dominated by quasi-free charge carriers. Our study suggests that charge-phonon coupling could serve as a proxy for the self-p-doping level, offering additional insights into fundamental charge-transport properties of tin halide perovskites and their potential optimization for photovoltaic applications.