Electron‐Beam Enables Spatially Resolved Defect‐Mediated Work Function Modulation in FAPbI 3 Perovskite Thin Films

ABSTRACT Modulation of the electronic energy levels in semiconducting materials is an essential technology for fabrication of advanced optoelectronic devices. Despite active studies on metal halide perovskite materials, a versatile modulation methodology capable of spatially uniform and controllable adjustment of the Fermi level remains elusive. Herein, we demonstrate that electron beam irradiation enables systematic tuning of work function in widely used formamidinium lead triiodide (FAPbI 3 ) perovskite thin films. The electron‐beam irradiation was found to induce iodine‐rich surface defect states, including interstitial iodine/polyiodide‐like species, thereby reducing the electron density near the Pb‐I coordination sites and leading to acceptor‐like surface electronic modulation. Variations in acceleration voltage and exposure time produced systematic work‐function modulation, reflecting the combined influence of incident electron energy and total electron dose on iodine‐related defect redistribution. Exploiting spatial controllability and local work function modulation, a lateral built‐in potential of 0.62 V in FAPbI 3 thin films was achieved. The proof‐of‐concept device based on the surface‐potential‐defined lateral junction formed by electron‐beam irradiation exhibited clear rectifying current–voltage behavior.