The O-Defective g-ZnO Sensor for VOC Gases: The Adsorption–Desorption, Electronic, and Sensitivity Properties

Adsorption-desorption performance, electronic properties, and sensitivity of O-defective g-ZnO (ODZO) gas sensors for volatile organic compounds (VOCs) are calculated using density functional theory and nonequilibrium Green's formalism. The VOCs are CH₂O, CH₄, C₂H₄O, CH₄O, and C₂H₆. The intrinsic g-ZnO (IZO) and ODZO exhibit strong adsorption capabilities for C₂H₄O and CH₄O. The IZO (0.118 e) and ODZO (0.059 e), which act as electron donors, exhibit the highest charge transfer to CH₂O, indicating a strong interaction. The VOCs adsorption on the IZO and ODZO systems maintain nonmagnetic semiconductor characteristics. Additionally, the introduction of an O-defect causes the adsorption energy and charge transfer amount of ODZO to show an overall decrease, indicating better desorption ability. Notably, the sensitivity results show that the ODZO gas sensors exhibit high sensitivity to CH₂O (39.3%), C₂H₄O (29.0%), and CH₄O (19.6%) at a voltage of 2.6 V, consistent with the adsorption-desorption performance and electronic properties.