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

The net enhancement of open-circuit voltage (V_oc) of dye-sensitized solar cells (DSSCs) was achievedwith the novel electrolyte composed of interhalogen based binary-redox couples without regard to thechoice of sensitizers. The interhalogen ion, I₂Br^-, was formed in the conventional iodine-based elec-trolyte 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 theelectrolyte shifted positively by the weighted-average of the two redox systems. It induced the increase of V _oc up to 30, 60, and 50 mV 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, withoutaffecting the short circuit current much. It corresponded to the enhancement of the overall power con-version efficiency (η) up to 8, 14, and 13%, respectively. Moreover, the degree of enhancement of V_oc was controllable by varying [I ₂Br^-] since the higher the contribution of [I ₂Br^-] the more positive shift in theenergy level of the binary redox couples.