Enhancing the Efficiency and Charge Transport Characteristics of Dye-Sensitized Solar Cells by Adding Graphene Nanosheets to TiO₂ Working Electrodes

In this study, TiO₂-GN nanocomposite working electrodes were fabricated by adding graphene nanosheets (GNs) to TiO₂ thin-film working electrodes. The influence of the thickness of the TiO₂ thin-film working electrodes on the efficiency and charge transport characteristics of the corresponding dye-sensitized solar cells (DSSCs) was investigated. A GN solution was spin-coated onto the TiO₂ thin films, which were then sintered at 100 °C in order to fabricate TiO₂-GN working electrodes. The characteristics of various working electrodes were analyzed via scanning electron microscopy, atomic force microscopy, surface profilometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. Moreover, the DSSCs fabricated from these working electrodes were characterized via current density-voltage, incident photo-to-current conversion efficiency, electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy measurements. The results indicate that adding GNs to TiO₂ thin films can enhance the electron transport rate and charge collection efficiency in TiO₂-GN working electrodes, and thereby increase the power conversion efficiency of DSSCs. As such, DSSCs containing the TiO₂-GN working electrodes exhibited an efficiency of 8.07%, which is 24.3% higher than that (6.49%) of the DSSCs containing conventional TiO₂ working electrodes