Aggregatoluminescence in perovskite precursors: insights into nanoaggregation and exciton dynamics in lead-halide systems

Perovskite materials have revolutionized optoelectronic technologies, yet a detailed understanding of the precursor aggregation processes and their impact on exciton dynamics remains elusive. Comprehensive insights into these fundamental photophysical processes are critical for the rational design and optimization of high-performance perovskite-based devices. Herein, we present a systematic investigation of the photophysical properties of PbX2 (X = Cl, Br, I) precursor aggregates in N, N-dimethylformamide. Steady-state optical measurements reveal that as the concentration increases, the absorption band edge undergoes a pronounced redshift, whereas the emission peak remains unchanged—a counterintuitive behavior we term “aggregatoluminescence.” Detailed spectral analyses, including excitation–emission mapping and lifetime measurements, suggest that this phenomenon originates from self-trapped exciton (STE) emission. Femtosecond transient absorption experiments further indicate an ultrafast conversion from free excitons to STEs mediated by strong electron-phonon coupling, as evidenced by nearly synchronous decay kinetics of the ground-state bleach and the excited-state absorption. Complementary single-crystal analyses demonstrate that the packing dimensionality critically influences the luminescence mechanism, with lower-dimensional structures more prone to STE formation. These insights underscore the pivotal role of precursor aggregation in directing exciton dynamics and lay a foundation for developing perovskite-based devices with enhanced performance and stability.