Relationship between diffusion of Co3+/Co2+ redox species in nanopores of porous titania stained with dye molecules, dye molecular structures, and photovoltaic performances
Abstract
Diffusion of Co2+ and Co3+ in nanopores of porous titania stained with various dyes were evaluated and were compared with those of I−, and I3−. Diffusion of Co3+ in the bare nanopore was slower than that of I3−. Dyes adsorbed on the wall of nanopores affected these diffusion coefficients remarkably. The Co3+ diffusion in nanopores became faster when the nanopore wall was covered with dyes with long alkyl groups, probably because the long alkyl groups suppress the interaction between TiO2 surface and Co3+. Higher open circuit voltage (Voc) was obtained for the DSSC with fast Co3+ diffusion in nanopores because the fast diffusion suppresses the charge recombination between electrons in titania and Co3+ remaining in the nanopores. The fast diffusion in nanopores was applied to thin nanoparticle spacer (th: 5 μm) of DSSCs. After nanoparticle spacer was stained with dyes with long alkyl groups, the efficiency drastically increased from 2.8% to 5.3%.
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