Hole Transfer Dynamics in Thin Films of Mixed‐Dimensional Quasi‐2D Perovskites

Abstract 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 (PEA ₂ MA _n−1 Pb _n I _3n+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.