Economical Pt-Free Catalysts for Counter Electrodes of Dye-Sensitized Solar Cells

Three classes (carbides, nitrides and oxides) of nanoscaled early-transition-metal catalysts have been proposed to replace the expensive Pt catalyst as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). Of these catalysts, Cr<sub>3</sub>C<sub>2</sub>, CrN, VC­(N), VN, TiC, TiC­(N), TiN, and V<sub>2</sub>O<sub>3</sub> all showed excellent catalytic activity for the reduction of I<sub>3</sub><sup>–</sup> to I<sup>–</sup> in the electrolyte. Further, VC embedded in mesoporous carbon (VC–MC) was prepared through in situ synthesis. The I<sub>3</sub><sup>–</sup>/I<sup>–</sup> DSC based on the VC–MC CE reached a high power conversion efficiency (PCE) of 7.63%, comparable to the photovoltaic performance of the DSC using a Pt CE (7.50%). In addition, the carbide catalysts demonstrated catalytic activity higher than that of Pt for the regeneration of a new organic redox couple of T<sub>2</sub>/T<sup>–</sup>. The T<sub>2</sub>/T<sup>–</sup> DSCs using TiC and VC–MC CEs showed PCEs of 4.96 and 5.15%, much higher than that of the DSC using a Pt CE (3.66%). This work expands the list of potential CE catalysts, which can help reduce the cost of DSCs and thereby encourage their fundamental research and commercial application.