Electrochemical approach to enhance the open-circuit voltage (Voc) of dye-sensitized solar cells (DSSCs)

Abstract

The net enhancement of open-circuit voltage (Voc) of dye-sensitized solar cells (DSSCs) was achieved with the novel electrolyte composed of interhalogen based binary-redox couples without regard to the choice of sensitizers. The interhalogen ion, I2Br−, was formed in the conventional iodine-based electrolyte by both chemically and electrochemically and it was found to produce an extra redox pair, (I−, Br−)/I2Br−, with new energy state at a more positive potential than that of I−/I3−. The Fermi level of the electrolyte shifted positively by the weighted-average of the two redox systems. It induced the increase of Voc up to 30, 60, and 50mV for cis-diisothiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II) bis(tetrabutylammonium) (N719), cis-dicyano-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) (Ruthenizer 505 or Ru505), and 2′,4′,5′,7′-tetrabromofluorescein (eosin Y) dyes, respectively, without affecting the short circuit current much. It corresponded to the enhancement of the overall power conversion efficiency (η) up to 8, 14, and 13%, respectively. Moreover, the degree of enhancement of Voc was controllable by varying [I2Br−] since the higher the contribution of [I2Br−] the more positive shift in the energy level of the binary redox couples.