Nb-doped TiO2 thin films for photovoltaic applications

• The Nb-doping and annealing in different environments improve the structure and conductivity of the TiO2 thin films.
• Annealing in H2 environment changes the Ti3 +/Ti4 + concentration ratio.
• n-ТіО2/p-CdTe heterojunction photovoltaic devices with efficiency of 1.8% were fabricated.

Polycrystalline titania and Nb:TiO2 thin films were deposited by RF magnetron sputtering. The influence of post-deposition annealing in vacuum and hydrogen atmosphere on the structure, morphology, oxidation states and optical properties was studied by X-ray diffraction, atomic force microscopy, XPS and UV–VIS spectroscopy. The heat treatment of titanium dioxide thin films in vacuum and H2 atmosphere induces structural and morphological changes. The band gap narrowing was observed for the transparent as-deposited Nb:TiO2 films, while annealing at 420 °C in H2 atmosphere resulted in an enhancement of the electrical conductivity. Further on, TiO2/p-CdTe photovoltaic devices with efficiency of 1.8% were fabricated and their characteristic ‘enhancement’ is discussed.

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