Halide Perovskite Single Crystals and Nanocrystal Films as Electron Donor‐Acceptor Heterojunctions

Abstract Halide perovskites are materials for future optical displays and solar cells. Electron donor‐acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined e‐beam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trapping‐assisted band gap engineering at the desired locations in MAPbBr 3 microrods, microplates, or nanocrystal thin films. The built‐in donor‐acceptor double and multi‐heterojunction structures let us transport and trap photogenerated charge carriers from wide‐band gap bromide to narrow‐band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single‐, double‐ and multi‐heterojunction donor‐acceptor halide perovskites for photovoltaic, photonic, and electronic applications.