Researchers at the University of Southern California have created a stable, nanocrystal form of solar cells that can exist as a liquid ink. The cells could be used to paint or print onto a clear surface, turning it into a solar panel. The technology may turn out to be important, as solar energy is turned to for more of the world's power.
This liquid state is possible because of the extremely small size of the nanocrystals that make up the cells. The nanocrystals are four nanometers in size, meaning each one is four billionths of a meter - over 250 billion of them could fit on the head of a pin. The nanocrystals can easily be floated in a liquid solution, creating the solar cell paint.
"While the commercialization of this technology is still years away, we see a clear path forward toward integrating this into the next generation of solar cell technologies," said Richard L. Brutchey, assistant professor of chemistry at USC. "...like you print a newspaper, you can print solar cells."
Until now, one of the problems with liquid nanocrystal solar cells is that, although they are less expensive to manufacture than single-crystal silicon wafer cells, they are less efficient at converting sunlight to electricity. This is because the organic ligand molecules used to keep the nanocrystals stable and separate them from each other also insulates the crystals, making them poor at conducting electricity. Brutchey and a postdoctoral researcher at USC named David H. Webber discovered a synthetic ligand that connects the nanocrystals to help transmit current.
The researchers also invented a low-temperature process that would allow the nanocrystal cells to be printed onto plastic without the worry of the plastic melting. In the future, this could mean flexible solar panels. Brutchey said his next plans for development are to work on nanocrystals built from materials other than cadmium, which is toxic and restricted for commercial applications.