Synergistic effect of thermal and chemical reduction of graphene oxide at the counter electrode on the performance of dye-sensitized solar cells

Abstract

Here, we present reduced graphene nanosheets (GNs) coated Fluorinated Tin oxide (FTO) glass, produced via combined thermal and chemical reduction as efficient counter electrode (CE) substrate for dye-sensitized solar cells (DSSCs). The FTO side of the counter electrode of the DSSC is spin coated by the as prepared 1.0% graphene oxide nanosheets (GONs) and is then reduced to GNs by the thermal reduction at 500 °C followed by chemical reduction, using hydrazine hydrate (HH), hydriodic acid (HI) and equal combination of both (HHI). For reference, conventional Platinum (Pt) based CE is also used. Structural and electrochemical properties of the formed GNs counter electrode are examined by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and photovoltaic measurements. It is found that the thermal reduction followed by the chemical reduction, as post treatment of the GNs coated CE, plays an important role in the quality of the electrochemical and photovoltaic performance of the DSSC. The reference Pt counter electrode based DSSC showed an overall photovoltaic conversion efficiency (PCE) of 8.565%. On the other hand, the proposed thermal and hydroiodic acid-treated GNs CE showed superlative PCE of 7.800%, which is found highest among other reducing agents used in the work, and only thermally reduced GNs counter electrode-based DSSC. Such an efficiency signifies that this GNs based electrode can be considered as in innovative and stable CE for applications involving the use of fabric-based energy conversion and storage devices, which cannot be reduced at elevated temperatures.