Self‐Powered Wide‐Narrow Bandgap‐Laminated Perovskite Photodetector with Bipolar Photoresponse for Secure Optical Communication

Abstract Perovskite photodetectors with bipolar photoresponse characteristics are expected to be applied in the field of secure optical communication (SOC). However, how to realize the perovskite photodetector with bipolar response remains challenging. Herein, by introducing bismuth iodide (BiI 3 ) into Sn‐Pb mixed perovskite precursor solution, 2D perovskite FA 3 Bi 2 I 9 is spontaneously formed at the bottom to realize a wide‐narrow bandgap‐laminated perovskite film. Wavelength‐dependent bipolar response is realized based on the absorption difference of the photoactive region with different bandgap combined with the carrier competition of the homotypic transport layer adopted in the as‐fabricated photodetector. Under the visible/near‐infrared (NIR) light irradiation, the bottom/top of the film generates a higher carrier concentration, where electrons are easier to be separated and transported by the SnO 2 /PC 61 BM to the bottom/top electrodes, respectively, resulting in a negative and positive bipolar response. Finally, based on positive NIR signal as the effective signal and negative visible signal as the interference signal, the SOC system is realized, where the positive NIR signal is well hidden by the negative visible signal. This work provides a simple and feasible strategy for fabrication of laminated perovskite films to achieve bipolar response.