Abstract
<title>Abstract</title> <p> Polar lattice structures and excitonic properties critically govern light-matter interactions and the distinctive functionalities of two-dimensional organic-inorganic hybrid perovskites (2D OIHPs). However, the multiscale coupling of organic-cation dynamics, inorganic-framework polarization, and electron-phonon interactions obscures the intrinsic relationship between lattice polarization and exciton behavior. Here, we disentangle these coupled effects by applying hydrostatic pressure to a homologous series of 2D perovskites, (iBA) <sub>2</sub> (A) <sub>2</sub> Pb <sub>3</sub> Br <sub>10</sub> (A = MA, EA, MHy). Continuous modulation of the interactions between intralayer A-site cations and the inorganic framework enables the concurrent tuning of lattice polarization and excitonic properties. We identify pressure-induced locking of the intralayer A-site cations and establish its pivotal role in governing lattice polarization. In the cation-locked state, lattice compression markedly enhances polarization; however, the large exciton binding energy precludes efficient exciton dissociation. Instead, the enhanced polarization further localizes excitons and accelerates their recombination, resulting in a shortened photoluminescence lifetime. These findings reveal a cation-dynamics-mediated causal relationship between lattice polarization and exciton behavior, bridging a critical mechanistic gap and providing a principled framework for the rational design of polar 2D perovskites with tailored excitonic properties. </p>