PEDOT:PSS assisted preparation of a graphene/nickel cobalt oxide hybrid counter electrode to serve in efficient dye-sensitized solar cells

Abstract

Graphene/nickel cobalt oxide (Gr/NiCo₂O₄) hybrids with a nanostructure were prepared by the use of an in situ hydrothermal route, and applied as a counter electrode (CE) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) assisted preparation (here abbreviated as P-A) in dye-sensitized solar cells (DSSCs) for the first time. The surface morphology of the bilayer TiO₂ photoanode was confirmed using scanning electron microscopy. The superior structural characteristics of the photoanode were advantageous to fast mass transport for the electrolyte, increasing the contact area between the electrolyte and active materials, and enabling the (P-A) Gr/NiCo₂O₄ CE to speed up the reduction of triiodide to iodide. Also, the CE with a superior nanostructure was evaluated by electrochemical characterization, which indicated that the (P-A) Gr/NiCo₂O₄ CE possessed excellent electrocatalytic activity in the iodide/triiodide electrolyte and a lower charge transfer resistance of 3.04 ± 0.02 Ω cm² compared to that of the Pt electrode (3.63 ± 0.02 Ω cm²). Under optimum conditions, the DSSC based on the (P-A) Gr/NiCo₂O₄ CE achieved a remarkable power conversion efficiency of 8.10%, which is about 8.7% higher than that of the Pt-based DSSC (7.45%). The (P-A) Gr/NiCo₂O₄ CE can be considered as a promising alternative CE for Pt-free DSSCs.