Effects of plant carotenoid spacers on the performance of a dye-sensitized solar cell using a chlorophyll derivative: Enhancement of photocurrent determined by one electron-oxidation potential of each carotenoid

Plant carotenoids (Cars) with 8–10 conjugated double bonds, having higher singlet energies than those of bacterial Cars with 9–13 conjugated double bonds, were added (by 20%) as redox spacers to a titania-based Grätzel-type solar cell using a chlorophyll derivative (PPB a) as the sensitizer. No clear indication of singlet-energy transfer from Car to PPB a was seen, but clear enhancement of photocurrent with the decreasing one electron-oxidation potential of Car was observed. An empirical equation correlating the increase in photocurrent to difference in one electron-oxidation potentials (PPB a minus Car) and the oscillator strength of Car is proposed.