PHOTOACOUSTIC, PHOTOELECTROCHEMICAL AND ULTRAFAST CARRIER DYNAMICS CHARACTERIZATION OF NANOSTRUCTURED TiO_2 ELECTRODES COMPOSED OF TiO_2 NANOPARTICLES WITH DIFFERENT SIZES SENSITIZED WITH CdSe QUANTUM DOTS

摘要

Significant progress in solar cell application has been made since 1990's using nanostructured TiO_2 electrodes adsorbed with organic dyes (dye sensitised solar cell: DSSC). In addition to organic dyes, semiconductor quantum dots (QDs) have also attracted significant interest as light harvesters in DSSCs. In this study, we investigate the effects of different size mixture of TiO_2 nanoparticles (15 and 27 nm) in nanostructured anatase-type TiO_2 electrodes on photoacoustic (PA), photoelectro-chemical current (PEC), and transient grating (TG) methods. We adsorbed CdSe QDs onto the electrodes as photosensitizer. Redshift of the PA spectra can be clearly observed and the PEC spectra showed the photosensitization in the visible region resulting from QDs absorption can be observed. Although the PA intensity of the spectrum shows a little increasing with the increase of the portion of 27 nm TiO_2, the PEC intensity increases largely with the increase of the portion of 27 nm particles. Also, ultrafast decay time of excited electrons in the CdSe QDs around 20 ps decreases with the increase of the portion of 27 nm particles, indicating the correlation with PEC.