Efficient Dye-Sensitized Solar Cells with Voltages Exceeding 1 V through Exploring Tris(4-alkoxyphenyl)amine Mediators in Combination with the Tris(bipyridine) Cobalt Redox System

Tandem redox electrolytes, prepared by the addition of a tris­(p-anisyl)­amine mediator into classic tris­(bipyridine)­cobalt-based electrolytes, demonstrate favorable electron transfer and reduced energy loss in dye-sensitized solar cells. Here, we have successfully explored three tris­(4-alkoxyphenyl)­amine mediators with bulky molecular structures and generated more effective tandem redox systems. This series of tandem redox electrolytes rendered solar cells with very high photovoltages exceeding 1 V, which approaches the theoretical voltage limit of tris­(bipyridine)­cobalt-based electrolytes. Solar cells with power conversion efficiencies of 9.7–11.0% under 1 sun illumination were manufactured. This corresponds to an efficiency improvement of up to 50% as compared to solar cells based on pure tris­(bipyridine)­cobalt-based electrolytes. The photovoltage increases with increasing steric effects of the tris­(4-alkoxyphenyl)­amine mediators, which is attributed to a retarded recombination kinetics. These results highlight the importance of structural design for optimized charge transfer at the sensitized semiconductor/electrolyte interface and provide insights for the future development of efficient dye-sensitized solar cells.