Self-assembled vertically stacked van der Waals In2O3/In2S3 heterojunction for ultra-sensitive room-temperature NO2 gas detection.

The development of IoT for smart cities has created a growing need for high-performance NO2 sensors for air quality monitoring. Van der Waals (vdW) heterostructures offer superior room-temperature gas sensing compared with their individual two-dimensional (2D) constituents, which has created a new paradigm for developing next-generation, high-performance gas-sensing devices. However, constructing ultrathin vdW heterostructures remains challenging and is primarily constrained to materials with layered crystal structures. Here, we report a vertically aligned 2D/2D vdW heterostructure composed of 3.1 nm-thick β-tetragonal In2S3 and 2.4 nm-thick cubic In2O3, fabricated via a solution-processed layer-by-layer self-assembly method. The heterostructure features a type-II band alignment, which effectively suppresses carrier recombination and thereby enhances NO2 detection performance at room temperature. A notable response of 27.3 to 10 ppm NO2 is achieved, surpassing those of pristine In2O3 and In2S3 by factors of 5.7 and 1.8, respectively. Furthermore, the sensor demonstrates outstanding selectivity, a low detection limit of 20.6 ppb, and excellent long-term stability. These superior sensing performances arise from optimized adsorption-desorption dynamics at the oxide/sulfide interface, enabled by the self-assembled vdW architecture. This study not only advances the scalable synthesis of 2D vdW heterostructures but also highlights interfacial engineering as a powerful strategy for designing next-generation, low-power gas sensors.