Density functional theory investigation of oxygen-deficient SnO2-x: Optoelectronic property tuning and hydrogen gas interaction.

Oxygen-vacancy engineering is an effective strategy for tailoring the electronic, optical, and gas-sensing properties of tin dioxide (SnO2). In this work, first-principles Density Functional Theory (DFT) calculations were performed to systematically investigate the influence of oxygen vacancies on the optoelectronic characteristics and hydrogen adsorption behavior of pristine SnO2 and oxygen-deficient SnO2-x. Oxygen-deficient structures were considered with SnO2-x (x = 0.02, 0.06, and 0.10), corresponding to oxygen-vacancy concentrations of 1%, 3%, and 5%, respectively. A 5 × 5 × 1 rutile SnO2 supercell containing 50 Sn and 100 O atoms was employed, and oxygen-deficient models were generated by removing 1, 3, and 5 oxygen atoms, yielding Sn₅₀O₉₉, Sn₅₀O₉₇, and Sn₅₀O₉₅ configurations. Electronic structure calculations reveal that oxygen vacancies introduce donor-like defect states near the conduction band, increasing carrier concentration and modifying the density of states. Projected density of states analysis confirms that these defect states originate primarily from the hybridization of Sn-derived orbitals with perturbed O 2p states surrounding the vacancy sites. The calculated optical properties demonstrate that oxygen deficiency enhances the refractive index, extinction coefficient, dielectric response, optical absorption, and reflectance, with the 3% oxygen-vacancy model exhibiting the most favorable overall optical performance. Hydrogen adsorption calculations performed on the thermodynamically stable SnO2(110) surface indicate that oxygen vacancies strengthen H2 adsorption by creating electronically active surface sites and facilitating charge transfer.