Mass Transport of Polypyridyl Cobalt Complexes in Dye-Sensitized Solar Cells with Mesoporous TiO2 Photoanodes

摘要

The diffusion of Co(DTB)3~(n+)(where DTB=4,4'-di-tert-butyl-2,2'~bipyridine)in dye-sensitized solar cells(DSSCs)was investigated.Current vs time experiments reveal that DSSCs with cobalt complex-based mediators display a qualitatively different response to the onset of illumination than do DSSCs with I~-/I3~-,exhibiting a sharp decline in the initial current over ~1 s or less.The results of these and other experiments conducted on DSSC sandwich cells are consistent with insufficient mass transport of Co(DTB)3~(3+)to the cathode,resulting in solution polarization and limited photocurrents.Rotating disk electrode voltammetry on Co(DTB)3~(n+)and I3~-in acetonitrile was performed to compare the rates of diffusion within bulk solution and typical mesoporous titania films.After accounting for viscosity differences,it was found that the effective diffusion coefficient of Co(DTB)3~(n+)through typical titania films in DSSCs is 0.5-3 X 10~(-7)cm~2 s~(-1),about 1 order of magnitude slower than I3~-.This difference may be attributed to the greater size and slower bulk diffusion of Co(DTB)3~(n+),greater viscosity of cobalt complex solutions,and a possible electrostatic surface interaction of Co(DTB)3~(n+)within the TiO2 film.