Photoluminescence Mapping of Mobile and Fixed Defects in Halide Perovskite Films

Halide perovskites exhibit coupled electronic-ionic properties that govern photovoltaic performance and stability; understanding ionic transport is, thus, essential for optimized photovoltaics. Characterizing ions with electrical techniques requires complete devices, yet electrical results are often dominated by interfacial effects over intrinsic ionic behavior. Here, localized-intensity-modulated photoluminescence spectroscopy (IMPLS) is used to optically probe ionic processes in a triple-cation, mixed-halide perovskite film. An analytical diffusion model is proposed to describe the IMPLS trends. The model indicates that mobile defects migrate laterally from high light intensity regions, with ionic diffusion coefficients extracted from IMPLS agreeing with the literature values. Moreover, spatially mapping IMPLS enables the separation of mobile and immobile defect contributions to the photoluminescence by quantifying the difference between the area-averaged photoluminescence intensity and phase shift. Ultimately, this work demonstrates that localized IMPLS provides a means to extract lateral ion diffusion coefficients while spatially distinguishing defect types across the sample.