Unraveling Charge and Energy Flow in Two-Dimensional Mixed Perovskites: Spatiotemporal Insights from Ultrafast Spectroscopy and Microscopy

Two-dimensional (2D) halide perovskites have emerged as promising materials for optoelectronic applications due to their excellent environmental stability and tunable band structures. Compositional engineering enables tailored optical and electronic properties while also introducing multiphase heterogeneity and energetic disorder. These complex energy landscapes profoundly influence charge and energy flow, making it challenging to resolve the transfer, trapping, and diffusion of photoexcited carriers across space and time. In this Perspective, we summarize recent progress in elucidating carrier dynamics in 2D mixed halide perovskites through ultrafast spectroscopy and microscopy. We highlight how dimensional engineering, cation doping, and halide mixing reshape charge/energy transfer and transport pathways, and emphasize the critical role of ultrafast spectroscopy and microscopy in visualizing these spatiotemporal processes. Additionally, we discuss the challenges and opportunities in tracking and modulating charge and energy flow for guiding device design. These insights guide mechanistic understanding and rational design of 2D mixed perovskite-based optoelectronic devices.