Imaging of Recombination Rates and Lifetime in Perovskite Thin Film Processing.

Large-scale fabrication and optimization of high-quality polycrystalline perovskite thin films present significant challenges in scientific research and industry. Shifting from single-spot measurements to imaging techniques facilitates the transition from laboratory-scale to large-scale processing. While single-spot photoluminescence (PL) methods provide high-depth insights into local optoelectronic characteristics, they are insufficient for assessing reliable information on homogeneity and spatial characteristics. Currently, no PL-based imaging method delivers a comparable level of information depth on charge carrier dynamics to single-spot PL methods. In response, this work introduces a non-invasive imaging technique based on double-pulse excitation. Varying the time delay between the pulses gives rise to spatial information on relative photoluminescence quantum yield (rPLQY) in thin films, yielding fundamental optoelectronic characteristics such as external radiative and effective non-radiative recombination rates and charge-carrier lifetime. Compared to traditional PL-imaging and k-imaging demonstrates the superiority of rPLQY-imaging in revealing charge carrier dynamics. This technique proves applicable across various sample configurations, irrespective of the presence of electrodes and charge transport layers. In addition, the method can estimate surface recombination velocity and variations in escape and parasitic absorption probabilities. Overall, the rPLQY-imaging method emerges as a valuable tool for scientific research aimed at characterizing and optimizing large-area perovskite thin films.