Dye Sensitized Solar Cells (DSSC)

Source: Dataweek.co.za, 3 September 2008,
Information from Frost & Sullivan Technical Insights

Nanotechnology has paved the way for the introduction or activation of unique characteristics in materials, by enhancing their physical and chemical properties. This core principle has been applied to carbon nanotubes (CNTs) by introducing defects that result in improved performance and optimised characteristics needed in other materials. CNTs offer properties such as electrical conductivity, chemical stability, high surface area, and optoelectronic properties that find applications in energy and storage technologies.

To study the effect of introducing CNTs in dye-sensitised solar cells (DSSC), researchers from Columbia University and Michigan State University have collaborated to replace the conventional platinum cathode in DSSCs with CNTs. DSSCs are a low-cost solar energy technology consisting of a photosensitive dye that absorbs photons from the sun and converts them to electrical charges which diffuse across the electrolyte to form an electric current. Prior research has resulted in using platinum deposited over transparent conducting oxide (TCO) as a cathode in DSSC to achieve high efficiency cells. However, the degradation of platinum over time poses a significant challenge in identifying the right material to maintain efficiency and operation over time. In this regard, the high conductivity and transparency of CNTs make them a potentially attractive option.

The research was aimed at identifying the responses of catalytic strength, transparency and sheet resistance of CNT films. The researchers deposited CNT films on a conducting substrate inside the cells and then monitored the electrochemical activity. They did this by using electrochemical impedance spectroscopy (EIS) of the charge-transfer resistance associated as a function of film transparency and loading. The films were then exposed to ultraviolet-generated ozone, resulting in a dramatic increase of catalytic activity.

This increase was attributed to defects that were introduced by the treatment with ozone. The defects appeared as pits that acted as sites for the chemical reaction, resulting in an increase of the reaction rate by more than 10 times. Conductivity and transparency was measured by varying and depositing CNTs of different sizes on substrates and incorporating them into the cells. This indicated that long nanotubes displayed higher and better conductivity and transparency.

“It shows that carbon nanotubes can be extremely effective catalysts,” said head researcher Jessica Trancik. “It also demonstrates a way in which nanostructuring materials can be used to shift tradeoffs between multiple properties, in order to make inexpensive materials behave in advanced ways. This is critical for the development of climate friendly energy technologies.”

The researchers anticipate the application of this research in DSSCs as well as possibly in batteries, fuel cells, sensors and other electroanalytical devices. The researchers believe that CNTs offer high flexibility and are less prone to cracking than TCO. This would make DSSCs easy to manufacture by roll-to-roll processing and integrate into various configurations.