How Exciton Interactions Control Spin-Depolarization in Layered Hybrid Perovskites

Using circularly polarized broadband transient absorption, time-resolved circular photoluminescence, and transient Faraday rotation spectroscopy, we report that spin-dependent interactions have a significant impact on exciton energies and spin depolarization times in layered Ruddlesden–Popper hybrid metal-halide perovskites. In BA₂FAPb₂I₇, we report that room-temperature spin lifetimes are largest (3.2 ps) at a carrier density of ∼10¹⁷ cm⁻³ with increasing depolarization rates at higher exciton densities. This indicates that many-body interactions reduce spin-lifetimes and outcompete the effect of D’yakonov-Perel precessional relaxation that has been previously reported at lower carrier densities. We further observe a dynamic circular dichroism that arises from a photoinduced polarization in the exciton distribution between total angular momentum states. Our findings provide fundamental and application relevant insights into the spin-dependent exciton–exciton interactions in layered hybrid perovskites.