Effect of Exciton Binding Energy on the Spin Relaxation of 2D Perovskite Polariton Microcavities

ABSTRACT Two‐dimensional lead halide organic perovskites (2D LHOP) offer a promising alternative for the study of room‐temperature exciton‐polaritons because of their strong exciton effect and high oscillator strength. In addition, 2D LHOP has also attracted great attention for spin‐related polaritonic devices owing to their strong spin‐orbit coupling. However, modulating the spin relaxation mechanisms in 2D LHOP still presents significant challenges. Herein, the net spin dynamics in 2D LHOP films and microcavities with different organic cations are studied by temperature‐dependent and pump fluence‐dependent circularly polarization‐resolved transient absorption (CP‐TA) measurements. For (EOA) 2 PbI 4 film with very small exciton binding energy, a slow spin relaxation (τ s ∼ 3.13 ps) is observed at low excitation densities and at high temperatures, which can be attributed to the strong polaronic states protection mechanism. While under high excitation densities or at low temperatures, the spin relaxation is governed by the Maialle‐Silva‐Sham (MSS) mechanism, leading to a very short net spin lifetime. Notably, inheriting the matter properties from their excitonic constituents, the polaronic states protection mechanism also plays an important role in the exciton‐polaritons, leading to a prolonged net spin lifetime in (EOA) 2 PbI 4 microcavities. The findings should serve as the fundamental understanding for future spin‐polaritonic devices.