Hole transfer dynamics in thin films of mixed-dimensional quasi-2D perovskites

The understanding of charge transfer processes in mixed-dimensional quasi-2D perovskites is crucial for their application in high-performance photovoltaic devices. In this work, the link between charge transport dynamics and morphology is investigated in a thin film of quasi-2D perovskites (PEA2MAn-1PbnI3n+1), grown with a distinct dimensionality gradient, where the n = 1 phase is concentrated near the substrate and phases with higher dimensionality progressively increase in concentration toward the surface. By selectively exciting the n = 4 phase, efficient hole transfer to the n = 2 and n = 3 phases occurring within a few tens of picoseconds after excitation is observed. In contrast, the n = 1 phase acts as a hole-blocking layer, limiting the overall charge transport efficiency. These results emphasize the critical importance of minimizing or eliminating the n = 1 layer to enhance charge carrier separation and transport, offering valuable insights into the optimization of quasi-2D perovskite-based solar cells.