A Self-Powered Photodetector Based on an Ambient-Air-Processed Cs3Bi2I9 Heterojunction for Optical Wireless Communication

The evolution toward a genuinely intelligent Internet of Things envisions future optical wireless networks anchored by extensive terminal nodes to facilitate pervasive sensing and communication. This vision places unprecedented demands on the underlying hardware, particularly in terms of scalability, energy efficiency, and cost-effectiveness. As the pivotal component within these terminal nodes, the system integrability and manufacturing cost of photodetectors are of critical importance. Accordingly, a Cs 3 Bi 2 I 9 /SnO 2 heterojunction photodetector was developed entirely via an ambient-air, solution-based technique. The device exhibits a spectral response from 365 to 520 nm and, at zero external bias, achieves a peak responsivity of 11.7 mA/W, a specific detectivity of 2.9 × 10 11 Jones, and a rapid response time of 33/52 μs. It retained its key performance metrics after more than 2160 h of storage in ambient air, demonstrating excellent long-term environmental stability. Under operational testing, only marginal performance degradation was observed after continuous illumination for over 4000 s, confirming its reliability for sustained use. As the core receiving device, it faithfully converted ASCII-encoded optical inputs into high-fidelity electrical signals, enabling accurate text recovery across three independent communication bands. This study provides a viable strategy for developing functional and sustainable photodetectors for open Internet of Things systems.