Lattice Control of Exciton Landscapes Enhances Energy Transport in 2D Perovskites

ABSTRACT Efficient charge and energy transport are crucial for light harvesting and energy conversion in optoelectronic devices based on two‐dimensional perovskites, yet it is often limited by the strong coupling between electronic excitations and lattice vibrations. Understanding how this coupling governs the balance between exciton localization and delocalization is therefore crucial for overcoming the intrinsic transport limitations in these materials. Here, we combine optical spectroscopy and time‐resolved photoluminescence imaging to investigate exciton transport in a series of n = 1 Ruddlesden–Popper perovskites with systematically varied lattice rigidity and exciton‐phonon coupling. We show that the competition between exciton delocalization and self‐trapping can be finely tuned through lattice‐controlled exciton energy landscape, resulting in distinct transport pathways ranging from thermally activated hopping in (BA) 2 PbI 4 to band‐like transport in (PEA) 2 SnI 4 . In particular, balanced exciton energetics in (PEA) 2 PbI 4 supports cooperative migration of both free and self‐trapped excitons, leading to enhanced diffusion compared with other n = 1 perovskites. These findings highlight the critical role of lattice composition in controlling exciton delocalization and demonstrate cooperative transport as an effective route to improving energy migration in two‐dimensional perovskites.