Ultrafast Energy Funneling in Two-Dimensional Mixed-Halide Perovskites Caused by Intrinsic Halide Immiscibility

Mixed halide perovskites (MHPs) have attracted great attention for photovoltaic and photonic applications due to their excellent photoelectric properties. Two-dimensional (2D) MHPs offer enhanced environmental stability and reduced halide ion migration compared with 3D analogs. However, 2D MHPs exhibit intrinsic halide immiscibility, leading to carrier aggregation and affecting device performance. A comprehensive understanding of carrier dynamics between the inherent distinct domains in 2D MHPs is essential. Herein, we conduct a detailed investigation of energy funneling in phenethylamine-based (PEA-based) 2D MHPs by using transient absorption spectroscopy. By tuning the Br/I ratio, heterogeneous mixtures are modulated with different domain contents. Energy funneling from high- to low-energy domains results in enhanced low-energy emission and increased radiative losses. Additionally, the competitive relationship between different energy funneling processes is influenced by the domain content. The finding reveals the impact of intrinsic halide immiscibility on carrier relaxation pathways and lifetimes in 2D MHPs, highlighting the significance of manipulating intrinsic halide mixtures to achieve high-performance 2D MHP optoelectronic devices.