In situ construction of CuInSe2–In2Se3 heterojunctions for highly selective self-powered NO2 sensors

Self-powered gas sensors are crucial for sustainable IoT systems but remain limited by detection thresholds, selectivity, and scalable fabrication methods. To overcome transfer-induced performance degradation in conventional fabrication of transition metal dichalcogenide (TMD) heterojunctions, herein we propose a direct in situ solid-phase conversion strategy to monolithic two-dimensional (2D) CuInSe2–In2Se3 thin-film heterojunctions. Under UV irradiation (365 nm), the heterojunction device exhibits self-powered operation with excellent selectivity and ultrafast response kinetics (2.36 s) toward 5 ppm NO2 at room temperature, with sensitivity comparable to that of leading-edge self-powered sensors. Significantly, our strategy eliminates the need for mechanical exfoliation and transfer steps, thereby ensuring robust device performance. This work offers perspectives on the rational design of planar heterojunctions for next-generation self-powered gas sensors, which are characterized by high performance, low cost, and energy efficiency.