In situ preparation of Ru-N-doped template-free mesoporous carbons as a transparent counter electrode for bifacial dye-sensitized solar cells

Abstract

The development of a highly active, long-lasting, and cost-effective electrocatalyst as an alternative to platinum (Pt) is a vital issue for the commercialization of dye-sensitized solar cells. In this study, Ru-N-doped template-free mesoporous carbon (Ru-N-TMC) was prepared by the direct stabilization and carbonization of the poly(butyl acrylate)-b-polyacrylonitrile (PBA-b-PAN) block copolymer and ruthenium(iii) acetylacetonate [Ru(acac)(3)]. During the stabilization process, microphase separation occurred in the PBA-b-PAN block copolymer due to the incompatibility between the two blocks, and the PAN block transformed to N-doped semi-graphitic carbon. In the carbonization step, the PBA block was eliminated as a porous template, creating hierarchal mesopores/micropores. Meanwhile, Ru(acac)(3) was decomposed to Ru, which was homogeneously distributed over the carbon substrate and anchored through N and O heteroatoms. The resulting Ru-N-TMC showed ultra-low charge transfer resistance (R-ct = 0.034 omega cm(2)) in the Co(bipyridine)(3)(3+/2+) reduction reaction, indicating very high electrocatalytic ability. Even though it is a transparent counter electrode (CE, average visible transmittance of 42.25%), covering a small fraction of the fluorine doped tin oxide (FTO)/glass substrate with Ru-N-TMC, it led to lower charge transfer resistance (R-ct = 0.55 omega cm(2)) compared to Pt (R-ct = 1.00 omega cm(2)). The Ru-N-TMC counter electrode exhibited a superior power conversion efficiency (PCE) of 11.42% compared to Pt (11.16%) when employed in SGT-021/Co(bpy)(3)(3+/2+) based dye-sensitized solar cells (DSSCs). Furthermore, a remarkable PCE of 10.13% and 8.64% from front and rear illumination, respectively, was obtained when the Ru-N-TMC counter electrode was employed in a bifacial DSSC. The outstanding catalytic activity and PCE of Ru-N-TMC were due to the high surface area of Ru-N-TMC, which contained numerous active species (Ru and N), easily facilitated to redox ions through the hierarchical microporous/mesoporous structure.