Crossover From Excitonic to Bulk Emission in Metal Halide Perovskite Nanocomposites

Abstract

Perovskite nanocomposites have emerged as an effective strategy to overcome instability of metal‐halide perovskites (MHPs) by embedding nanocrystals (NCs) within host matrices while preserving their optoelectronic properties. However, this approach often results in morphologically heterogeneous systems with broad size distributions and aggregation. This heterogeneity yields complex, co‐existing recombination pathways that conventional ensemble measurements fail to disentangle. Here, we investigate highly emissive MAPbBr 3 ‐Ni(AcO) 2 nanocomposite thin films using time‐resolved photoluminescence (TRPL) and photoluminescence quantum yield (PLQY) mapping as a function of pulse repetition rate and excitation fluence. By systematically varying the perovskite concentration, we induce a morphological transition from isolated NCs to bulk‐like aggregates and observe a shift from excitonic to free charge carrier recombination regimes. PLQY mapping under varying excitation conditions enables selective probing of distinct recombination pathways, allowing the dominant size population governing the photophysics to be identified. We find that even a minor nanocrystalline fraction with efficient radiative recombination can dominate the overall photophysical response, masking bulk‐like behavior. This highlights the critical role of morphological heterogeneity in governing the apparent photophysical properties of perovskite ensembles and demonstrates that conventional ensemble averaging fails to resolve the underlying charge carrier dynamics, an insight essential for the design of perovskite‐based optoelectronic systems.