Photovoltage in nanocrystalline porous TiO2 -: art. no. 075204

Transient and spectral photovoltage (PV) is investigated in nanocrystalline porous TiO2, which belongs to a class of materials with a very low electrical conductivity, i.e., with a huge Maxwell relaxation time. The PV in such materials is caused by diffusion of excess charge carriers with different diffusion coefficients. Usually, the diffusion coefficient for electrons is larger than that for holes in porous TiO2. The PV transients are strongly retarded in time with respect to the exciting light pulse. The retardation of the photovoltage transients becomes stronger with decreasing size of the interconnected TiO2 nanoparticles and generation of defect states. The band gap of porous TiO2 (rutile, anatase) and the preferential formation of electron traps below the band gap are analyzed.