Quantifying Evolving Defect Parameters in Metal Halide Perovskites via the Measurement and Modeling of Power‐Dependent Transient Photoluminescence

ABSTRACT Dynamic photoinduced defect states in metal halide perovskites (MHPs) critically govern the non‐equilibrium photophysics, metastability, and long‐term performance of optoelectronic devices, such as solar cells. This metastability is evident in steady‐state photoluminescence experiments, where the amplitudes increase or decrease depending on the environmental and excitation conditions. Here, we combine excitation‐dependent time‐resolved photoluminescence (trPL) measurements with parameter estimation via Bayesian optimization coupled with a full Shockley–Read–Hall and diffusion model to quantitatively track defect state formation in Cs 0.05 FA 0.95 PbI 3 thin films, under continuous 1 sun illumination. This methodology is applied to quantify the evolution of defect distributions in absorbers with two distinct initial optoelectronic qualities, leveraging the sensitivity of trPL decays to defect‐assisted non‐radiative recombination processes. We show that 21 h of continuous illumination causes the slopes of the differential‐lifetime/mean carrier‐density plots to converge from initially distinct decay behaviors, which we interpret as a convergence of dominant recombination mechanisms following irradiation. The fitting results further suggest the emergence of trapping species with highly asymmetric capture cross‐section ratios. Overall, this study establishes a general diagnostic methodology for tracking carrier‐induced degradation pathways in perovskites and other emerging semiconductors.