Solar-Blind UV and NIR Bipolar Photodiode for 10 ⁶⁹ Key Space Optical Encryption

Owing to the complementary advantages of distinct spectral bands, such as solar-blind ultraviolet (UV) with the near-zero-background interference and near-infrared (NIR) with low atmospheric propagation loss, multiband photodetector offers a more effective approach for security enhancement of optical image encryption compared to conventional single-band systems. To translate this strategic potential into a practical hardware platform, we demonstrate a back-to-back photodiode composed of narrow-bandgap PbSe and wide-bandgap CsPbBr3 bipolar heterojunction, which provides a bias-switched spectral response in solar-blind UV and NIR bands. Consequently, a dual-band optical image encryption is achieved via a highly uniform photodiode array, leading to a key space of 1069 which is several orders of magnitude higher than that in existing systems such as Se0.25Te0.75/Si photodiode and the p-GaN/(In,Ga)N heterojunction. Furthermore, a solar-blind UV and NIR image encryption task is performed by integrating multiple bipolar photodiode arrays on a single chip, facilitating the development of low-loss and high-security communication systems.