Ultrafast exciton-polaron dynamics in 2D Ruddlesden-Popper lead-halide perovskites

Two-dimensional Ruddlesden-Popper (2D RP) hybrid perovskites exhibit enhanced chemical and structural stability compared with three-dimensional (3D) counterparts, making them attractive for optoelectronic applications. However, a quantitative understanding of coupled free-exciton (FE) and exciton-polaron (EP) dynamics in strict monolayer ( n = 1) RP perovskites remains limited. Here, we report a systematic investigation of FE-EP branching, interconversion, and interactions in monolayer 2D RP perovskites using femtosecond transient absorption spectroscopy. Thin films with different organic spacers and fabrication routes are comparatively analyzed. We find EP binding energies of 50–65 meV in (BA) 2 PbI 4 and 37–39 meV in (PEA) 2 PbI 4 , together with a kinetic FE-EP balance persisting for tens of picoseconds. Films fabricated by the newly developed route exhibit weaker Auger annihilation and reduced hot-phonon bottlenecks, consistent with fewer traps and impurities. Rate-equation modeling quantitatively reproduces the coupled ultrafast dynamics.