Revealing Different Types of Grain Boundaries in Perovskite Films by Intensity-dependent Fluorescence Lifetime Imaging Microscopy

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