**3.2 Graphene**

Andre Konstantin Geim and Konstantin Sergeevich Novoselov of the University of Manchester received the 2010 Nobel Prize in Physics for their pioneering research on graphene. Graphene is a flat monolayer of carbon atoms arranging like the structure of honeycombs with one atom thickness. Due to the special thickness, graphene is considered as a 2D material, as shown in **Figure 2**. Carbon atoms in graphene lattice are hybridized sp2 with the C-C bond length of 1.42 Å. Graphene is one of the basic carbon allotropes, including graphite, carbon nanotube, and fullerene. Graphene possesses not only all properties of graphite but also other extraordinary characteristics. Graphene has high carrier mobility at room

**299**

FTO [5].

*Graphene-Based Material for Fabrication of Electrodes in Dye-Sensitized Solar Cells*

V−1 s−1), high specific area (2630 m2

thermal conductivity (~3000 Wm−1 K−1), high Young modulus (~1 TPa), and high optical transparency (97.7%). Moreover, although graphene has low-density, it is up

Because graphene is an atom-thick layer, it is a perfect nanoscale material and, therefore, has great potential in a very wide range of applications in the field of nanotechnology. Graphene has been extensively studied for nano-technological applications in field-effect transistors, solar cells, fuel cells, supercapacitors, rechargeable batteries, optical modulators, chemical sensors, drug delivery, and

There are numerous methods for synthesis of graphene: mechanical exfoliation,

chemical vapor deposition, epitaxial growth, chemical reduction, etc. [28, 29]. Among these methods, chemical reduction is a commonly used route for graphene synthesis. In this method, graphene is synthesized by reduction of graphene oxide (GO), which has the similar structure to graphene, with oxygen-containing functional groups introduced into the hexagon structure of graphene sheets. The synthesized graphene by this method is called rGO. Chemical reduction method is a cost-effective and widely available method for the mass production of rGO compared with thermal reduction and other methods. Otherwise, the synthesis procedure of graphene with bottom-up methods has revealed difficulty for applications in industry [30]. In this study, GO was synthesized from graphite (Gi) using

In DSSCs, cathode carries out three functions. As a catalyst, the cathode facilitates the regeneration of redox couple i.e., the oxidized state of redox couple is reduced by accepting electrons at the surface of the electrode. As a positive electrode of primary cells, the cathode collects electrons from the external circuit and transfers electrons into the cell. As a mirror, unabsorbed light came through the photoanode and the electrolyte, which was partially reflected in the cell to enhance

The cathode in DSSCs conventionally includes two parts: the substrate and the catalytic layer. The type of substrate mostly used in DSSCs is conductive glass substrates made by coating a layer of TCO on transparent glass. In DSSCs, the TCO substrate plays an important role in transmitting the incident light and leading the electrical current. Both transmittance and conductivity are crucial for the electrode of DSSCs. The conductive glass that is widely used in the fabrication of DSSCs is

For promoting the commercialization of DSSCs, the production cost of DSSCs needs to be reduced. Moreover, the efficiency of DSSCs is expected to maintain at an acceptable level. At present, Pt is still the most appropriate material for the fabrication of cathode in DSSCs. However, this noble metal has limited availability and relatively high cost that hinder the large-scale production of DSSCs. Moreover, Pt cathodes show poor resistance toward corrosion in iodide solution, which may result in the formation of PtI4. The use of Pt in cathodes is considered as one of many reasons that prevent the commercialization of DSSCs. On the other hand, carbon is the material that can be found everywhere on the planet. Carbon-based materials had wide applications in technology including solar technology [5]. Recently, graphene has been explored as a novel material with many outstanding characteristics, which makes these materials become one of the most promising alternatives of Pt in DSSCs. In recent years, graphene and graphene-based materials have been demonstrated to be an adequate substitute for Pt, to cut off the use of

g−1), excellent

*DOI: http://dx.doi.org/10.5772/intechopen.93637*

to 50 times stronger than steel [24, 25].

biomedical applications, in addition to other areas [26, 27].

the Hummers' method and GO was reduced to create rGO.

**3.3 Graphene for fabrication of cathodes in DSSCs**

the utilization of the light [5, 31].

temperature (~200,000 cm2

**Figure 2.** *Structure of graphene.*

### *Graphene-Based Material for Fabrication of Electrodes in Dye-Sensitized Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.93637*

temperature (~200,000 cm2 V−1 s−1), high specific area (2630 m2 g−1), excellent thermal conductivity (~3000 Wm−1 K−1), high Young modulus (~1 TPa), and high optical transparency (97.7%). Moreover, although graphene has low-density, it is up to 50 times stronger than steel [24, 25].

Because graphene is an atom-thick layer, it is a perfect nanoscale material and, therefore, has great potential in a very wide range of applications in the field of nanotechnology. Graphene has been extensively studied for nano-technological applications in field-effect transistors, solar cells, fuel cells, supercapacitors, rechargeable batteries, optical modulators, chemical sensors, drug delivery, and biomedical applications, in addition to other areas [26, 27].

There are numerous methods for synthesis of graphene: mechanical exfoliation, chemical vapor deposition, epitaxial growth, chemical reduction, etc. [28, 29]. Among these methods, chemical reduction is a commonly used route for graphene synthesis. In this method, graphene is synthesized by reduction of graphene oxide (GO), which has the similar structure to graphene, with oxygen-containing functional groups introduced into the hexagon structure of graphene sheets. The synthesized graphene by this method is called rGO. Chemical reduction method is a cost-effective and widely available method for the mass production of rGO compared with thermal reduction and other methods. Otherwise, the synthesis procedure of graphene with bottom-up methods has revealed difficulty for applications in industry [30]. In this study, GO was synthesized from graphite (Gi) using the Hummers' method and GO was reduced to create rGO.
