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China Makes Solar Cell Breakthrough

A team of Chinese researchers have reached a new record of 8.2% light conversion efficiency in solvent-free dye-sensitized solar cells, according to a paper that appeared online today in the journal Nature Materials.

Dye-sensitized solar cell technology is a promising alternative to expensive silicon solar cells. The dye-sensitized cells mimic natural photosynthesis processes seen in plants and algae. The cells are made up of a porous film of tiny (nanometer sized) white pigment particles made out of titanium dioxide. The latter are covered with a layer of dye which is in contact with an electrolyte solution. When solar radiation hits the dye it injects a negative charge in the pigment nanoparticle and a positive charge into the electrolyte resulting in the conversion of sunlight into electrical energy.

This breakthrough in efficiency without the use of volatile organic solvents will make it possible to pursue large scale, outdoor practical application of lightweight, inexpensive, flexible dye-sensitized solar films that are stable over long periods of light and heat exposure. The cells are inexpensive, easy to produce and can withstand long exposure to light and heat compared with traditional silicon-based solar cells.

Currently, state-of-the-art dye-sensitized cells have an overall light conversion efficiency greater than 11%, still about two times lower than silicon cell technology. A major drawback to the dye-sensitized cell technology is the electrolyte solution, which is made up of volatile organic solvents and must be carefully sealed. This, along with the fact that the solvents permeate plastics, has precluded large-scale outdoor application and integration into flexible structures.

To overcome this hurdle, the researchers developed a mixture of three solid salts as an alternative to using organic solvents as an electrolyte solution. When the three solid components are mixed together in the right proportion they dissolve into a stable melt. These electrolyte mixtures could lead to large-scale practical application of dye-sensitized solar cell technology.

The team was led by Michael Graetzel, Shaik Zakeeruddin and colleagues from the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences