Transparent Conductive Anatase Nb-Doped TiO ₂ Obtained via Annealing in Ambient Air

Anatase Nb-doped TiO2 (TNO) has emerged as a promising material for transparent electrodes and durable protective coatings for fuel cells. The conventional fabrication method involves sputter-deposition of amorphous precursor thin films, followed by vacuum annealing to induce crystallization. Atmospheric annealing is highly desired for practical applications. However, there has been no report on the fabrication of TNO thin films via annealing in ambient air. In this study, we demonstrate a process for fabricating low-resistance TNO thin films using sputtering and annealing in ambient air. Amorphous films are deposited under reduced oxygen partial pressures and subsequently annealed at 420 °C in air. This process yields transparent conductive films with a low room-temperature resistivity of 1.2 × 10–3 Ω·cm and a high internal transmittance above 90% in the visible range. Electron-transport property measurements and X-ray absorption spectroscopy reveal that surface carrier depletion extends to ∼30 nm, while the inner region retains a high carrier density.