| Summary: | We developed cobalt and carbon complex materials as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) to replace conventional platinum (Pt) CEs. Co12 and Co15, both of which are basic cobalt derivatives, showed good redox potential with a suitable open-circuit voltage (V<sub>OC</sub>); however, their poor electrical conductivity engendered a low short-circuit current (J<sub>SC</sub>) and fill factor (FF). Mixing them with carbon black (CB) improved the electrical conductivity of the CE; in particular, J<sub>SC</sub> and FF were considerably improved. Further improvement was achieved by combining cobalt derivatives and CB through thermal sintering to produce a novel CoCB material as a CE. CoCB had good electrical conductivity and electrocatalytic capability, and this further enhanced both J<sub>SC</sub> and V<sub>OC</sub>. The optimized device exhibited a power conversion efficiency (PCE) of 7.44%, which was higher than the value of 7.16% for a device with a conventional Pt CE. The conductivity of CoCB could be further increased by mixing it with PEDOT:PSS, a conducting polymer. The device’s J<sub>SC</sub> increased to 18.65 mA/cm<sup>2</sup>, which was considerably higher than the value of 14.24 mA/cm<sup>2</sup> for the device with Pt CEs. The results demonstrate the potential of the cobalt and carbon complex as a CE for DSSCs.
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