Revealing Different\nTypes of Grain Boundaries in Perovskite\nFilms by Intensity-dependent Fluorescence Lifetime Imaging Microscopy

Grain boundaries (GBs) in polycrystalline perovskite\nfilms play\na crucial role in determining photogenerated carrier transport and\nrecombination, thereby impacting both efficiency and stability of\nperovskite solar cells (PSCs). Despite extensive research into grain\nboundary engineering to optimize PSC performance, the specific mechanisms\nthrough which GBs influence carrier dynamics remain unclear and highly\ndebated. Here, we employ high-resolution, intensity-dependent fluorescence\nlifetime imaging microscopy (FLIM) to systematically investigate the\nbehaviors of different types of GBs in hybrid perovskite films under\nvarying light conditions. Our analysis reveals three distinct categories\nof GBs: I-type, which remains invisible at low excitation intensities\nand exerts minimal influence on carrier transport; W-type, characterized\nby a W-shaped lifetime profile at high light intensities, suggesting\nsignificant carrier scattering at the boundary; and V-type, marked\nby a V-shaped lifetime profile, indicating a more specialized role\nin regulating carrier dynamics. These findings provide critical insights\ninto how various GBs modulate photogenerated carrier behavior, offering\na new framework for understanding their diverse impacts on the optoelectronic\nproperties of perovskite films. Our results underscore the importance\nof targeted grain boundary engineering strategies to advance the design\nand optimization of next-generation perovskite-based photonic and\noptoelectronic devices.