Binary redox electrolytes used in dye-sensitized solar cells

[Display omitted] Fast dye-regeneration and slow charge recombination are prerequisites for selecting superior redox couples of electrolytes to obtain highly efficient dye-sensitized solar cells (DSSCs). Although the ubiquitous combination of the I−/I3− redox couple demonstrates high power conversion efficiency (PCE), it suffers from several limitations such as a large potential difference of approximately 560 mV between the Fermi level of I−/I3− and the HOMO level of the N719 dye as well as high visible light absorption. These limitations cause inefficient dye-regeneration and significantly enhance the back reaction rate of photoelectrons to I3− in the electrolyte. This review discusses recent progress in the conception and device performance of different binary redox couples in DSSCs based on lowering potential differences, the back reaction of photo-induced electrons, the absorption of visible light, and improvement of dye-regeneration. We specifically focus on recent strategies targeted for effectively increasing both the open circuit voltage of DSSCs up to ˜100 mV and the PCE to above 10%; these strategies include introduction of binary redox couples or additional redox species to conventional iodine-based electrolytes. Moreover, we propose future directions for the further development of binary redox couples with advanced concepts for achieving DSSCs with high performance and high stability.