Imaging Ultrafast Charge Transfer at Low-Dimensional Lead Halide Perovskite Heterostructures

Addressing interface physics and related photoinduced dynamics is crucial to understand charge carrier paths and losses and ultimately design efficient optoelectronic devices. However, such dynamics are often masked when bulky systems are investigated. In this work, we combine photoluminescence with ultrafast transient absorption microscopy to map charge transfer processes in few-layers-thick heterostructures made of low-dimensional (C 6 H 5 CH 2 CH 2 NH 3 ) 2 (CH 3 NH 3 ) n-1 Pb n I 3n+1 perovskite flakes of different dimensionalities ( n = 3) and ( n = 1). We observe that the hole transfer process from the ( n = 3) to the ( n = 1) phase happens after exciton diffusion on a time scale of tens of picoseconds, whereas electron transfer is hindered by the high exciton binding energy and low diffusion coefficient within the ( n = 1) phase. This study sets the stage for a deeper understanding needed for the smart development of new heterostructure combinations with different dimensionalities and band alignments.