Photoassisted electrical transport in porous TiO2

Abstract

The photoassisted electrical transport is investigated in porous TiO 2 (anatase) layers by impedance spectroscopy (IS) and time-of-flight (TOF) at different temperatures and pressures of oxygen. The experiments were carried out under the conditions of zero bias potential (no electron injection at the contacts takes place) and of relatively high bias potential when electrons are injected from the contact into the porous TiO 2 layer. Illumination with photons having energies below the band gap leads to a strong increase of the conductivity while the conductivity is practically unchanged for illumination with ultra violet light independent of the applied bias potential. Besides the light induced excess carrier generation, TOF measurements show an increase of the drift mobility under illumination with blue light. The results were explained by the lowering of the barriers between sintered TiO 2 nanocrystals due to separation of photoexcited charge carriers.