We demonstrate control of the optoelectronic properties of vanadium oxide nanoparticle thin films and devices by tailoring the oxygen vacancy concentration via redox reaction with SnCl₂ at 65 °C. The redox process alters the crystal structure to produce disordered mixed-valence materials with structural signatures of a-V₂O₅ and Sn⁴⁺ incorporation. We demonstrate that the SnCl₂ chemistry is effective on both solution-processed inks of V₂O₅ nanoparticles or mesoporous films cast from untreated inks, enabling versatile routes towards functional films with tunable optoelectronic properties. Two terminal planar devices, Au/mesoporous a-V₂O₅/Au, were fabricated and systematically examined for their current-voltage characteristics. As the concentration of SnCl₂ or the duration of SnCl₂ treatment increases, the number of oxygen vacancies and Sn⁴⁺ in the lattice correspondingly rises, indicating a heightened presence of free electrons in the host lattice. Consequently, the resistance decreases from 1.1 MΩ to 0.42 MΩ with a rise in SnCl₂ concentration from 0 to 0.1 M. Similarly, the resistance diminishes from 1.1 MΩ to 0.44 MΩ with an increase in treatment duration from 0 to 90 minutes. This work provides a valuable demonstration of tailoring vanadium-oxygen systems through top-down chemical manipulation from known thermodynamic phases rather than bottom-up synthesis of exotic phases.

<b>a</b>) Visualization of the a-V<sub>2</sub>O<sub>5</sub> based on ICSD 15798. Thin black box highlights the a-V<sub>2</sub>O<sub>5</sub> unit cell. O<sub>t</sub> = terminal oxygen, O<sub>b</sub> = bridging oxygen, O<sub>c</sub> = chain oxygen.<b> b</b>) Photographs showing V<sub>2</sub>O<sub>5</sub> dispersion color change as a function of concentration and reaction time at 65 °C in an inert N<sub>2</sub> environment.

a) Visualization of the a-V₂O₅ based on ICSD 15798. Thin black box highlights the a-V₂O₅ unit cell. O_t = terminal oxygen, O_b = bridging oxygen, O_c = chain oxygen. b) Photographs showing V₂O₅ dispersion color change as a function of concentration and reaction time at 65 °C in an inert N₂ environment.

Jeffrey Blackburn

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