There is now a potential pathway to cheap, stable solar cells made from nanocrystals so small they can exist as a liquid ink and paint or print onto clear surfaces.
The solar nanocrystals are about four nanometers in size — meaning you could fit more than 250,000,000,000 on the head of a pin — and float them in a liquid solution, so “like you print a newspaper, you can print solar cells,” said Richard L. Brutchey, assistant professor of chemistry at the University of Southern California Dornsife College of Letters, Arts and Sciences.
Brutchey and USC postdoctoral researcher David H. Webber developed a new surface coating for the nanocrystals, which consist of the semiconductor cadmium selenide.
Liquid nanocrystal solar cells are cheaper to fabricate than available single-crystal silicon wafer solar cells but are not nearly as efficient at converting sunlight to electricity. Brutchey and Webber solved one of the key problems of liquid solar cells: How to create a stable liquid that also conducts electricity.
In the past, organic ligand molecules attached to the nanocrystals to keep them stable and to prevent them from sticking together. These molecules also insulated the crystals, making the whole thing terrible at conducting electricity.
“That has been a real challenge in this field,” Brutchey said.
Brutchey and Webber discovered a synthetic ligand that not only works well at stabilizing nanocrystals, but actually builds tiny bridges connecting the nanocrystals to help transmit current.
With a relatively low-temperature process, the researchers’ method also allows for the possibility solar cells can print onto plastic instead of glass without any issues with melting – resulting in a flexible solar panel that can shape to fit anywhere.
As they continue their research, Brutchey said he plans to work on nanocrystals built from materials other than cadmium, which often ends up restricted in commercial applications due to toxicity.
“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,” Brutchey said.