Photosensitization of nanostructured TiO2 with CdSe quantum dots: effects of microstructure and electron transport in TiO2 substrates

Four sample types of nanostructured titanium dioxide (TiO2) electrodes were studied, variously prepared with TiO2 nanocrystalline particles of different sizes (15 and 27 nm in diameter) and with the addition of polyethylene glycol (PEG) binders having two different molecular weights (MW) (20,000 and 500,000). CdSe nanoparticles (CdSe quantum dots: CdSe QDs) were adsorbed on to each of the four types of TiO2 electrode using a chemical deposition technique. Photoacoustic (PA) and photoelectrochemical (PEC) current spectra were measured, together with the incident photon to current conversion efficiency (IPCE). The photosensitization by the CdSe QDs was confirmed. It was found that the PEC current and IPCE are strongly dependent on the TiO2 nanoparticle size and the MW of PEG in the TiO2/water paste. The correlation of the PEC and IPCE with the microstructure and the electron diffusion coefficient for each of TiO2 nanostructured electrode type are discussed, providing information which could lead to the optimization of dye-sensitized solar cells (DSSC).