Photoacoustic, photoelectrochemical current, and photoluminescence spectra of highly porous, polycrystalline TiO2 electrodes fabricated by chemical synthesis

We report the effect of the application of a voltage in a concentrated KCI electrolyte on photoacoustic (PA), photoelectrochemical current (PEC), and photoluminescence (PL) spectra for the preparation of highly porous, polycrystalline TiO2 electrodes. The intensities of the PA spectra of the TiO2 electrode with the voltage treatments are larger than those without the treatments below the bandgap region, suggesting a decrease of scattering and/or an increase of the carrier concentration by the voltage treatments. The modulation frequency dependence of the PA intensity above the bandgap of the former is different from the Latter in the low-frequency region, indicating a good contact (namely, the reduction of interface states) between the TiO2 film and the substrate (Ti metal). Also, the modulation frequency dependence of the PA phase above the bandgap region of the former is different from the latter, suggesting larger thermal conductivity of the TiO2 electrode with the voltage treatments than that without treatments. The intensity of the PEC spectrum of the TiO2 electrode with the voltage treatments is threefold that without the treatments above the bandgap region, also suggesting good contact (namely, the reduction of interface states). Although the peak positions in the PL spectra are in agreement with each other, the PL intensity of the TiO2 electrode with the voltage treatments is higher, suggesting the increase of the radiative recombination center owing to the increase of donor levels formed by partially reduced Ti ions. (C) 2000 Elsevier Science S.A. All rights reserved.