Unconventional Biexciton Dynamics in Superradiant Perovskite Quantum Dots Driven by Many‐Body Correlations

ABSTRACT Excitons and biexcitons emission traits, for example, quantum yield, lifetime, and coherence, govern device performance metrics including brightness, optical gain thresholds, and the efficiency of single‐ and entangled‐photon generation. Biexcitons are conventionally understood to radiatively decay more rapidly than excitons. This view stems largely from studies in strongly confined quantum dots (QDs), where inter‐exciton correlations are often neglected. In contrast, weakly confined systems such as large CsPbBr 3 QDs exhibit significant Coulomb correlations, necessitating a revised framework for biexciton radiative dynamics, one that has remained incomplete due to limited experimental insights. Here, we combine single‐particle photoluminescence (PL) spectroscopy with effective‐mass variational quantum Monte Carlo (VQMC) simulations to directly probe the biexciton geometry, exciton–phonon interactions, and radiative decay in CsPbBr 3 QDs across a range of sizes and temperatures. We reveal that the biexciton‐to‐exciton radiative decay lifetime ratio is strongly modulated by inter‐exciton correlations, with a striking inversion of the expected decay lifetime hierarchy in the weak‐confinement regime. Specifically, at cryogenic temperatures, biexcitons exhibit anomalously longer radiative lifetime (148 ± 30 ps) than excitons (106 ± 16 ps), challenging conventional models. These findings uncover a correlation‐driven regime of multiexciton physics and suggest new routes for tailoring light–matter interactions for classical and quantum photonic applications.