Infrared radiation effects in TiO2 nanostructured films

We present results of the influence of infrared radiation on metal–TiO2–metal junctions where the metal electrodes are composed of conducting SnO–SnO2 on glass substrates. An amount of 10–30 μm oxide films are obtained by deposition of TiO2 from a colloidal suspension followed by heating sinterization of grains. The morphology of the films have been studied by AFM analysis and result in an array of weakly separated grains of average diameter 30 nm. In the dark, the devices show open-circuit voltages of few millivolt, with slight increase under solar light illumination. The voltages exhibit strong sensitivity, oscillatory behaviour and polarity reversibility due to external changes of the radiation. Such a photovoltaic effect can be explained either as a mesoscopic voltage arising from the nanograins under thermal radiation or as resonances due to pair tunnelling between the nanograins where high Tc locally develops.