Optical Absorption, Photoelectrochemical, and Ultrafast Carrier Dynamic Investigations of TiO₂ Electrodes Composed of Nanotubes and Nanowires Sensitized with CdSe Quantum Dots

TiO 2 electrodes composed of nanotubes and nanowires are prepared from TiO 2 gels using a surfactant-assisted self-assembly method reported earlier. CdSe quantum dots (QDs) are adsorbed onto the TiO 2 electrodes by chemical deposition (CD). Their average size increases from 4 to 6 nm with increasing deposition time from 3 to 82 h. The optical absorption and incident photon-to-current conversion efficiency (IPCE) of the electrodes are studied by photoacoustic (PA) and photoelectrochemical (PEC) methods. The photosensitization of the TiO 2 electrodes by CdSe QDs is demonstrated by both PA and IPCE spectra. The ultrafast carrier dynamics of the CdSe-sensitized TiO 2 electrodes composed of nanotubes and nanowires is studied using a lens-free heterodyne detection transient grating (LF-HD-TG) technique. Fast and slow decay processes with lifetimes of about 3 ps and 60–130 ps, respectively, are observed.