Solution-Processed p-SnSe/n-SnSe₂ Hetero-Structure Layers for Ultrasensitive NO₂ Detection

The formation of semiconductor heterostructures is an effective approach to achieve high performance in electrical gas sensing. However, such heterostructures are usually prepared via multi-step procedures. In this contribution, by taking advantage of the crystal phase-dependent electronic property of SnSe_x based materials, we report a one-step colloid method for the preparation of SnSe(x%)/SnSe₂(100−x%) p–n heterostructures, with x ≈30, 50, and 70. The obtained materials with solution processability were successfully fabricated into NO₂ sensors. Among them, the SnSe(50 %)/SnSe₂(50 %) based sensor with an active layer thickness of 2 μm exhibited the highest sensitivity to NO₂ (30 % at 0.1 ppm) with a limit of detection (LOD) down to 69 ppb at room temperature (25 °C). This was mainly attributed to the formation of p–n junctions that allowed for gas-induced modification of the junction barriers. Under 405 nm laser illumination, the sensor performance was further enhanced, exhibiting a 3.5 times increased response toward 0.1 ppm NO₂, along with a recovery time of 4.6 min.