Illuminating Lead Coordination in Perovskite Precursors via Fluorescence Spectroscopy

The properties of perovskite precursors critically determine the ultimate performance of perovskite devices, yet simple and accessible real-time precursor characterization methods remain scarce. Here, we systematically investigate the Pb coordination environment in perovskite precursors using fluorescence spectroscopy. By examining lead halide [PbX6]⁴⁻ octahedra (X = Cl, Br, I) and monitoring their luminescence under different solvents and A-site cation compositions, we unveil how [PbX6]4- distinct aggregation states give rise to characteristic fluorescence “fingerprints.” We find that halide choice, solvent coordination, and A-site cations collectively exert pronounced effects on the photoluminescence (PL) peak positions, full width at half maximum (FWHM), and photoluminescence quantum yield (PLQY). Moreover, we demonstrate that fluorescence spectroscopy can capture subtle changes in intermediate perovskite structures—including low-dimensional nanoscale clusters and the formation of higher-dimensional networks. This robust optical method offers a powerful and straightforward approach for tracing the nucleation stage, evaluating solvent-solute and solute–solute interactions, and differentiating Pb coordination states in real time.