Light-Induced Defect State Dynamics on Perovskite Film Surface Revealed by Quasi-In Situ Photocarrier Radiometry

Light-induced defect dynamics critically affect the optoelectronic performance and stability of perovskite, yet their kinetic evolution and surface origin remain insufficiently understood because of limited in situ quantitative characterization. Here, a quasi-in situ photocarrier radiometry (QI-PCR) approach is developed to probe and quantify light-induced defect evolution in perovskite films. Stronger excitation intensity accelerates photoluminescence intensity decrease (PLID), whereas lowering the temperature within the investigated range suppresses PLID and favors photoluminescence intensity enhancement (PLIE), with a clear PLIE-to-PLID crossover at intermediate temperatures. The light-induced response is largely reversible in dark and strongly dependent on excitation conditions. Quasi-in situ fitting quantifies the effective lifetime (τeff) and surface recombination velocity (SRV). Under 405 nm excitation at 100 mW cm-2, the surface defect density (Nt) estimated from SRV increases from 4.8 × 109 to 2.53 × 1010 cm-2 within 210 s at 300 K but decreases from 8.95 × 109 to 5.0 × 109 cm-2 at 250 K. Based on this mechanism, an ultrathin LiF layer suppresses PLID, increasing the PLID time constant from 57 to 384 s and reducing Nt from 2.53 × 1010 to 2.4 × 109 cm-2 under the same excitation intensity. This work establishes QI-PCR as a sensitive and practical method for tracking light-induced surface defect dynamics in perovskite films, providing deeper insight into the origin of light-induced instability and methodological support for optimizing stable perovskite devices.