Integrated Strategy toward Self-Powering and Selectivity Tuning of Semiconductor Gas Sensors

Inorganic conductometric gas sensors struggle to overcome limitations in high power consumption and poor selectivity. Herein, recent advances in developing self-powered gas sensors with tunable selectivity are introduced. Alternative general approaches for powering gas sensors were realized via proper integration of complementary functionalities (namely, powering and sensing) in a singular heterostructure. These solar light driven gas sensors operating at room temperature without applying any additional external powering sources are comparatively discussed. The TYPE-1 gas sensor based on integration of pure inorganic interfaces (e.g., CdS/n-ZnO/p-Si) is capable of delivering a self-sustained sensing response, while it shows a nonselective interaction toward oxidizing and reducing gases. The structural and the optical merits of TYPE-1 sensor are investigated giving more insight into the role of light activation on the modulation of the self-powered sensing response. In the TYPE-2 sensor, the selectivity of inorganic materials is tailored through surface functionalization with self-assembled organic monolayers (SAMs). Such hybrid interfaces (e.g., SAMs/ZnO/p-Si) have specific surface interactions with target gases compared to the nonspecific oxidation–reduction interactions governing the sensing mechanism of simple inorganic sensors. The theoretical modeling using density functional theory (DFT) has been used to simulate the sensing behavior of inorganic/organic/gas interfaces, revealing that the alignment of organic/gas frontier molecular orbitals with respect to the inorganic Fermi level is the key factor for tuning selectivity. These platforms open new avenues for developing advanced energy-neutral gas sensing devices and concepts.