Mechanism of Particle Size Effect on Electron Injection Efficiency in Ruthenium Dye-Sensitized TiO2 Nanoparticle Films

The kinetics and efficiency of the electron injection process for TiO2 nanoparticle films composed of different particle sizes (d = 9, 20, 30, 50, 169, 200, and 400 nm in diameter) sensitized by N3 dye (Ru(dcbpy)(2)(NCS)(2)) were investigated by using time-resolved fluorescence spectroscopy and femtosecond (transmittance and diffuse reflectance) transient absorption spectroscopy. Different electron injection efficiencies were obtained for different diameter systems. Small diameter systems gave the high electron injection yields, which were around 90%, whereas larger diameter systems gave low efficiencies from 35 to 70%. Judging from the comprehensive and systematic time-resolved spectroscopic data, we concluded that N3 aggregates that formed in spaces between larger diameter TiO2 nanoparticles were responsible for the low efficiencies.