http://www.digitaljournal.com/science/graphene-helps-to-construct-flexible-solar-cells/article/416760

Graphene helps to construct flexible solar cells

Posted Nov 22, 2014 by Tim Sandle
Researchers have devised a new type of cathode that could be readily used to manufacture inexpensive, flexible dye-sensitized solar cells.
Lark Energy s Hawton Solar Farm becomes UK’s Largest to Connect to Electricity Network.
Lark Energy's Hawton Solar Farm becomes UK’s Largest to Connect to Electricity Network.
Lark Energy
The issue is about making more robust and less expensive dye-sensitized solar cells. These cells use organic dyes, drawn from various fruits (raspberries are the most commonly used). The dyes are then used to coat conductive titanium dioxide particles. The dyes absorb photons and produce electrons that flow out of the cell for use. From this, a return line completes the circuit to the cathode that combines with an iodine-based electrolyte to refresh the dye.
The new cathode tube (one of the two electrodes found in batteries) was prepared from nanotubes seamlessly bonded to graphene. The idea is to replace the brittle platinum-based materials found in many solar cells.
Graphene is an exciting material. Consisting of a single layer of carbon atoms arranged in a honeycomb lattice, the material is extremely stable, flexible, highly conductive, and of particular interest for electronic applications.
The process of bonding graphene was the most complex part. A technique was designed to grow very long bundles of aligned carbon nanotubes. With this process, the nanotubes remained attached to the surface substrate but pushed the catalyst up as they grew.
The advantages are that graphene and nanotubes are grown directly onto the nickel substrate that serves as an electrode. This avoids adhesion issues that commonly occur with current processes. A second factor is that the hybrid also has less contact resistance with the electrolyte, allowing electrons to flow more freely.
In trials, the new solar cells can produce almost 18 milliamps of current per square centimetre. This is far superior to platinum based cells.
The research was conducted at Rice University. The findings have been published in Journal of Materials Chemistry A. The research is titled “Vertically Aligned Carbon Nanotubes/Graphene Hybrid Electrode as a TCO- and Pt-Free Flexible Cathode for Application in Solar Cells.”