SnS₂ Quantum Dot-Based Optoelectronic Flexible Sensors for Ultrasensitive Detection of NO₂ Down to 1 ppb

Transition-metal dichalcogenides (TMDs) have gained intense interest for their outstanding optoelectronic and electrochemical characteristics, utilized in versatile applications such as gas sensors and photodetectors. However, TMD-based chemiresistors suffer from poor sensitivity at ppb-level detection, and the experimental detection limit fails to reach 1 ppb. Herein, SnS₂ QD/graphene nanoheterostructures as functional flexible sensors are fabricated for NO₂ gas and light detection at room temperature. The semiconductor type of the nanohybrids can be shifted between p-type and n-type by adjusting the proportion of the components, both of which exhibit excellent gas-sensing properties. The ppb-level NO₂ detection is realized even under room temperature with superior sensitivity (860% to 125 ppb), fast response (114 s), and recovery (166 s). It also demonstrates ultrahigh sensitivity and broadband photodetection in the visible region. The photoresponsivity can reach upto 2.08 × 10³ A/W under blue light illumination and under room temperature. Especially, the influence of light illumination of different wavelengths and intensities on gas-sensing performance is studied. Red light (1 mW/cm²) greatly enhances the sensitivity up to 5.1 folds, and the device performs obvious response to NO₂ at concentrations as low as 1 ppb. Ab initio density functional theory calculation and band theories are applied to explain the interaction of the components and the effect of the light excitation inducing charge carriers on gas-sensing equilibrium.