Dye-sensitized solar cells [DSSCs] have emerged as the next generation of photovoltaic devices, offering several advantages, including moderate light-to-electricity conversion efficiency, easy fabrication, and low cost [1–4]. Generally, a DSSC is composed of a mesoporous nanocrystalline film (normally titanium oxide), to whose surface is attached a monolayer of the charge-transfer dye molecule, an electrolyte containing a dissolved iodide/tri-iodide redox couple, and a counter electrode. The role of counter electrodes is to transfer electrons from the external circuit to the tri-iodide and iodine in the redox electrolyte . Most commonly, Pt counter electrodes are utilized; however, despite their excellent properties, they suffer from several limitations, e.g., difficulty in large-scale production and high economic cost. Carbon nanomaterials provide a promising alternative to Pt owing to their intrinsic attractive features, notably their high electrical conductivity, corrosion resistance, and excellent electrocatalytic activity, as well as their increasingly affordable cost.
The application of various carbon nanomaterials, such as carbon blacks, carbon nanotubes, and graphenes, to counter electrodes has been widely documented in the literature [6–12]. We reported that chemically converted graphene-based carbon nanocomposites and chemical-vapor-deposited graphene-based carbon nanocomposites had energy conversion efficiencies of 3.0% and 4.46%, respectively. However, several difficulties such as low cost and mass production process have hampered the realization of these materials as a counter electrode for DSSCs [13, 14].
In order to overcome those problems, we investigated counter electrodes fabricated with three different carbon-based materials such as graphene, single-walled carbon nanotubes [SWNTs], and graphene-SWNT composites using electrophoretic deposition [EPD]. The EPD method is an automated and high-throughput process that has been widely employed in the industry; it can provide a homogeneous and robust film on the surface of the substrate [15–17]. Herein, we present fabrication and characterization results of counter electrodes of graphene, SWNTs, and graphene-SWNT composites by the EPD method using a dispersion solution of CNTs and graphene.