Lin, QingzhuoBoukhvalov, Danil W.Li, HuiLi, YongxiJiao, MengyangGao, SihanHumphrey, Mark G.Zhang, ChiHuang, Zhipeng2025-12-232025-12-23https://hdl.handle.net/1885/733796877Dual-band photodetectors are gaining increasing attention for their potential in diverse applications, particularly in optical wireless communication (OWC). In this context, photodetectors capable of simultaneously detecting visible (VIS) and deep ultraviolet (DUV) bands show great promise for enhancing data security by concealing secret key signals. However, the construction of such devices remains a significant challenge. In this study, a novel one-step synthesis of CsAgBr2/Cs2AgBiBr6 heterocrystals is reported, via a partial chemical transformation strategy, enabling the construction of a self-powered dual-band photodetector with excellent performance. The device exhibits remarkable responsivities of 0.16 A W−1 at 265 nm (DUV region) and 0.06 A W−1 at 440 nm (VIS region) under zero external bias, with high external quantum efficiencies of 74.9% and 17.8%, respectively. These outstanding optoelectronic properties stem from the strong built-in electric field within the heterocrystal structure. Furthermore, it is demonstrated that this dual-band functionality significantly improves OWC security by effectively filtering interfering signals and capturing secret keys and passwords, highlighting the combined role of DUV and VIS in synergistically enabling secure communication. This work not only provides a new approach for the synthesis of lead-free perovskite heterocrystals but also contributes to the development of next-generation secure OWC technologies based on dual-band photodetectors.Z. Huang acknowledges support from the National Natural Science Foundation of China (Nos. 62275197 and 51772214), the Natural Science Foundation of Shanghai (23ZR1465700), the National Youth Talent Support Program of China (No. W03070073), and the Fundamental Research Funds for the Central Universities. C. Zhang acknowledges support from the National Natural Science Foundation of China (No. 51432006), the Ministry of Education of China for the Changjiang Innovation Research Team (No. IRT14R23), the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (No. B13025), and the Innovation Program of Shanghai Municipal Education Commission. D. W. Boukhvalov acknowledges support from the Jiangsu Innovative and Entrepreneurial Talents Project, and the Ministry of Science and Education of the Russian Federation (Project FEUZ\u20102023\u20100013). M. G. Humphrey thanks the Australian Research Council (DP170100411).10en© 2025 The Author(s)deep ultravioletdual-band self-powered photodetectorheterojunctionlead-free perovskiteoptical communication202510.1002/adom.202500868105009828019