Reduced graphene oxide–Ta3N5 composite: a potential cathode for efficient Co(bpy)33+/2+ mediated dye-sensitized solar cells

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Abstract
Polypyridine complexes of Co(II)/Co(III) coupled with donor–π bridge–acceptor structured organic dyes are by far the most promising route to boost the efficiency of dye-sensitized solar cells (DSSCs). We report herein the first investigation of Ta3N5 nanorods incorporated on reduced graphene oxide (RGO) sheets as a counter electrode for application in Co(bpy)3 3+/2+ (bpy = 2,2′-bipyridine) mediated DSSCs. RGO–Ta3N5 composite was fabricated by mixing graphene oxide (GO) with pre-synthesized Ta3N5 nanorods (aspect ratio of ∼3) followed by facile hydrazine hydrate reduction. The composite film on conductive glass was prepared by a drop-casting process at room temperature without heat treatment. Compared with a Pt cathode with a power conversion efficiency of 7.59%, RGO–Ta3N5 exhibited comparable electrocatalytic performance for the reduction of Co(bpy)3 3+ species and better electrocatalytic stability in Co(bpy)3 3+/2+ acetonitrile solution, which was attributed to the synergetic catalytic effect of RGO and Ta3N5 nanorods and the high electrical conductivity derived from the RGO network, resulting in a power conversion efficiency of 7.85%. The present result is expected to lead to a family of composites for highly efficient cathode materials.

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