Effect of Quantum Well Thickness on Long‐Range Exciton Transport in Two‐Dimensional Layered Perovskites

ABSTRACT Quantum well thickness ( n ) is a crucial parameter for tailoring exciton properties in 2D layered perovskites, yet the governing transport mechanisms remain insufficiently understood. Herein, we employed transient absorption microscopy to investigate exciton dynamics and in‐plane diffusion of (PEA) 2 (MA) n −1 Pb n I 3 n +1 ( n = 1 – 4) microplates. With increasing n , reduced quantum confinement significantly suppresses both exciton recombination and exciton‐exciton annihilation rates. The low‐energy photoinduced absorption changes from a long‐lived feature to a short‐lived response that rapidly turns into bleaching, evidencing the transition from localized polaronic states to delocalized excitons. Importantly, the exciton diffusion coefficient exhibits a non‐monotonic dependence on n , with (PEA) 2 (MA) 3 Pb 4 I 13 achieving the maximum value of 2.38 cm 2 s −1 and a diffusion length of 1.41 µm due to increased structural rigidity and reduced exciton‐phonon coupling. These findings highlight quantum well thickness as a key parameter in regulating exciton transport and provide essential insights for the design of high‐performance excitonic devices.