Tunable Bipolar Perovskite Photodiodes Enabled by Electric Field Flipping for Secure Optical Communication

(electron transport layer) interface is precisely modulated, resulting in flipping of the overall device electric field, driving carriers generated at different depths toward opposite electrodes, and producing a wavelength-dependent bipolar response. In particular, tuning the internal electric field expands the positive response range from 300-480 nm to 300-700 nm. A secure optical communication system constructed by this bipolar photodiode can transmit positive and negative signals, enabling the secure transmission of Fourier-transformed color images. The optical communication system demonstrated excellent security. When intercepted by unipolar photodiodes, the information leakage rate is only 10.85%, and the difference rate of transmitted images reaches a perfect 100%. This work utilized an interfacial potential engineering strategy to fabricate tunable bipolar perovskite photodiodes, offering a promising route toward compact, high-speed, and intrinsically secured optoelectronic communication systems.