Transparent TiO<sub>2</sub>/MoO<sub>3</sub> Heterojunction-Based\nPhotovoltaic Self-Powered Triethylamine Gas Sensor with IoT-Enabled\nSmartphone Interface

Conventional gas sensors encounter a significant obstacle\nin terms\nof power consumption, making them unsuitable for integration with\nthe next generation of smartphones, wireless platforms, and the Internet\nof Things (IoT). Energy-efficient gas sensors, particularly self-powered\ngas sensors, can effectively tackle this problem. The researchers\nare making significant strides in advancing photovoltaic self-powered\ngas sensors by employing diverse materials and their compositions.\nUnfortunately, several of these sensors seem complex in fabrication\nand mainly target oxidizing species detection. To address these issues,\nwe have successfully employed a transparent, cost-efficient solution\nprocessed bilayer TiO<sub>2</sub>/MoO<sub>3</sub> heterojunction-based\nphotovoltaic self-powered gas sensor with superior VOC sensing capabilities,\nmarking a significant milestone in this field. The scanning Kelvin\nprobe (SKP) measurement reveals the remarkable change in contact potential\ndifference (−23 mV/kPa) of the TiO<sub>2</sub>/MoO<sub>3</sub> bilayered film after UV light exposure in a triethylamine (TEA)\natmosphere, indicating the highest reactivity between TEA molecules\nand TiO<sub>2</sub>/MoO<sub>3</sub>. Under photovoltaic mode, the\nsensor further demonstrates exceptional sensitivity (∼2.35\n× 10<sup>–3</sup> ppm<sup>–1</sup>) to TEA compared\nto other studied VOCs, with an admirable limit of detection (22 ppm)\nand signal-to-noise ratio (1540). Additionally, the sensor shows the\nability to recognize TEA and estimate its composition in a binary\nmixture of VOCs from a similar class. The strongest affinity of TiO<sub>2</sub>/MoO<sub>3</sub> toward the TEA molecule, the lowest covalent\nbond energy, and the highest electron-donating nature of TEA may be\nmainly attributed to the highest adsorption between TiO<sub>2</sub>/MoO<sub>3</sub> and TEA. We further demonstrate the practical applicability\nof the TEA sensor with a prototype device connected to a smartphone\nvia the IoT, enabling continuous surveillance of TEA.