Interfacial Field‐Engineered Perovskite/Silicon Bipolar Photodiodes with Wavelength‐Tunable Polarity for Dual‐Channel Encrypted Optical Communication

ABSTRACT Bipolar photodiodes that generate opposite photocurrent polarities at different wavelengths offer an attractive device‐level route toward secure optical communication, yet their practical use is hampered by limited design generality and fixed spectral switching points. Here, we report a self‐powered perovskite/silicon tandem bipolar photodiode in which the polarity‐switching wavelength can be continuously tuned from 520 to 780 nm by engineering the boron doping profile in the p + ‐Si emitter. The competition between the built‐in electric fields of the Si p‐n junction and the perovskite/transport‐layer interfaces is reconfigured, enabling deterministic control of both the sign and magnitude of the photocurrent under zero bias. The optimized devices feature the fastest response speed (∼2 µs) and the lowest noise current (∼10 −13 A Hz −1/2 ) among reported bipolar photodetectors. The field‐competition strategy is further shown to be compatible with multiple perovskite compositions, highlighting its universality for wavelength‐reconfigurable optoelectronics. Leveraging two devices with complementary bipolar responses under ultraviolet and near‐infrared illumination, we construct a dual‐channel hardware‐encrypted optical communication system capable of faithfully recovering audio signals with an information leakage rate below 0.04%. This work establishes a general design principle for interfacial field engineering in multijunction semiconductors, opening a pathway toward self‐powered, wavelength‐programmable, and hardware‐secure photonic systems.