Transparent TiO₂/MoO₃ Heterojunction-Based Photovoltaic Self-Powered Triethylamine Gas Sensor with IoT-Enabled Smartphone Interface

Conventional gas sensors encounter a significant obstacle in terms of power consumption, making them unsuitable for integration with the next generation of smartphones, wireless platforms, and the Internet of Things (IoT). Energy-efficient gas sensors, particularly self-powered gas sensors, can effectively tackle this problem. The researchers are making significant strides in advancing photovoltaic self-powered gas sensors by employing diverse materials and their compositions. Unfortunately, several of these sensors seem complex in fabrication and mainly target oxidizing species detection. To address these issues, we have successfully employed a transparent, cost-efficient solution processed bilayer TiO₂/MoO₃ heterojunction-based photovoltaic self-powered gas sensor with superior VOC sensing capabilities, marking a significant milestone in this field. The scanning Kelvin probe (SKP) measurement reveals the remarkable change in contact potential difference (-23 mV/kPa) of the TiO₂/MoO₃ bilayered film after UV light exposure in a triethylamine (TEA) atmosphere, indicating the highest reactivity between TEA molecules and TiO₂/MoO₃. Under photovoltaic mode, the sensor further demonstrates exceptional sensitivity (∼2.35 × 10^-3 ppm^-1) to TEA compared to other studied VOCs, with an admirable limit of detection (22 ppm) and signal-to-noise ratio (1540). Additionally, the sensor shows the ability to recognize TEA and estimate its composition in a binary mixture of VOCs from a similar class. The strongest affinity of TiO₂/MoO₃ toward the TEA molecule, the lowest covalent bond energy, and the highest electron-donating nature of TEA may be mainly attributed to the highest adsorption between TiO₂/MoO₃ and TEA. We further demonstrate the practical applicability of the TEA sensor with a prototype device connected to a smartphone via the IoT, enabling continuous surveillance of TEA.