Electrolytes Based on Binary-Redox Couples for High Voltage Dye-Sensitized Solar Cells

We prepared the interhalogen and halogen-pseudohalogen based electrolytes with multiple redox couples for high voltage dye-sensitized solar cells (DSSCs) and it was characterized by different electrochemical techniques. It was found that the additional interhalogen or halogen-pseudohalogen based redox systems, (I^-, Br^-)/I₂Br^- or (I^-, SCN^-)/I₂(SCN)^- can be formed by both chemically and electrochemically. The electrochemical redox potential for these both couples is more positive than that of conventional iodide-triiodide system while the redox reaction involved with these ions were essentially comparable to that of I^-/I₃^- in the conventional DSSC. Therefore, the formation of these redox couples produces extra redox states at more positive potential than I^-/I₃^- couple, which contributed to increase the open circuit voltage (V_oc) of DSSCs by shifting positively the equilibrium potential of solution phase. The interhalogen based redox couple increased open circuit voltage (V_oc) significantly regardless of sensitizing dyes, which corresponded to 14% higher overall power conversion efficiency (h) compared to that with conventional iodine based redox couple. However, the degree of potential shift, so the corresponding V_oc, can be controlled by adjusting the ratio of the concentrations of these redox species in the solution phase. This study is offering a very promising strategy to develop a novel electrolyte of which the energy level can be controlled by introducing an additional redox species with more positive potentials without compromising the rate of regeneration of dyes.