Photosensitized growth of TiO ₂ nanoparticles improved the charge transfer dynamics of a bichromophoric dye

Nanostructured TiO ₂ particles utilized in dye-sensitized solar cells (DSSCs) provide a large surface area, which facilitates the adsorption of sensitizing dye and charge recombination due to the high density of surface traps. In this article, a modified surface of TiO ₂ nanoparticles was successfully synthesized in the presence of (1-hydroxycyclohexyl)(phenyl) methanone (HCPM) as a sensitizer to control formation in a toluene/ethanol medium via a photolytic process. A particle-size analysis showed that the oxides which had fully oxidized to TiO ₂ were 20∼35 nm in diameter. The structure of the TiO ₂ particles being of an amorphous nature and the nearly defect-free distributions of Ti ⁴ and O ^2- energy levels imply that the grain boundaries and surface trap sites were effectively suppressed. TiO ₂ particles were subsequently blended with the bichromophoric dye, AMIP, to study fluorescence decay dynamics between AMIP/TiO ₂ interfaces. Fluorescence lifetime measurements gave the rate constant for the charge-transfer process from the excited singlet of AMIP to the conduction band of TiO ₂ as 1.2×10 ⁹ s ^-l. When PL quenching measured as the TiO ₂ contents of these composites reached a 2.5 wt% level, the maximum enhanced charge-transfer dynamics occurred. Structural properties and photophysical behaviors of composites of AMIP bound to TiO ₂ were extensively demonstrated.