Developing an efficient material as a counter electrode (CE) with excellent catalytic activity, intrinsic stability, and low cost is essential for the commercial application of dye-sensitized solar cells (DSSCs). Photovoltaic properties of DSSCs fabricated with cost-effective, platinum-free CEs composed of various carbon allotrope mixtures—including graphite (GR), activated carbon (AC), and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films—were systematically investigated. DSSCs assembled with PEDOT:PSS/GR/AC showed an impressive photovoltaic conversion efficiency of 4.60%, compared to 4.06% for DSSCs with GR/AC CE or 1.66% for PEDOT:PSS alone or 6.56% for Pt under the illumination 100 mW cm−2 (AM 1.5 G) due to the superior electrocatalytic activity and the conductivity of AC and PEDOT:PSS. The fabricated carbon counter electrodes were extensively characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, cyclic voltammetry (CV), Tafel measurements, and electrochemical impedance spectroscopy (EIS). The CV, EIS, and Tafel measurements indicated that the PEDOT:PSS/GR/AC composite film has low charge-transfer resistance on the electrolyte/CE interface and high catalytic activity for the reduction of triiodide to iodide than the GR/AC CEs. It is potentially feasible that such a carbon configuration can be used as a counter electrode, replacing the more expensive Pt in DSSCs.
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