Harvesting Photons in the Infrared. Electron Injection from Excited Tricarbocyanine Dye (IR-125) into TiO2 and Ag@TiO2 Core−Shell Nanoparticles

TiO2 and Ag@TiO2 core shell nanoparticles have been modified with a carbocyanine dye (IR-125) to extend the photoresponse in the near-infrared. Upon binding dye molecules to TiO2, we observe a sharp decrease in the fluorescence yield. The electron injection into TiO2 was found to dominate the deactivation of the excited singlet state. The rate constant for the charge injection process as determined from the decay of the excited singlet is ∼1011 s-1. In the case of Ag@TiO2, the electrons injected into the TiO2 layer are quickly transferred to the Ag core. The metal core in Ag@TiO2 did not alter the forward charge-transfer kinetics, but it influenced the back electron transfer. The regeneration of the dye involving the reaction between the oxidized dye and injected electron was a factor of 2 slower for Ag@TiO2 than the TiO2 system. Use of composite nanoparticles comprised of a metal core semiconductor shell may provide new ways to modulate charge recombination processes in dye-sensitized solar cells.