When the University of Utah’s Department of Metallurgical Engineering decided to get a new microwave oven for the kitchen, Prashant Sarswat, a research associate, thought there had to be a good use for the old one. He found one: making semiconductor solar cells.
Microwaves are used in some types of metallurgy, as well as for synthesizing certain types of organic compounds. But those applications use much more sophisticated (and expensive) equipment. Sarswat showed it’s possible to make high quality, nanocrystal semiconductors with an inexpensive kitchen model.
Nanocrystal semiconductors don’t use the rare and sometimes toxic metals that many conventional semiconductors do. They could make more efficient photovoltaic solar cells and LED lights, or biological sensors and thermoelectric devices that turn waste heat into electricity.
The semiconductor Sarswat made is known as CZTS, for copper, zinc, tin and sulfur. To make CZTS, salts of the metals are dissolved in a solvent and then heated in the microwave. That forms a liquid, like ink, with suspended nanocrystals of CZTS. It took only eight minutes to form the crystals, though 18 minutes seemed to make them of a more uniform size.
The crystals themselves ranged from three nanometers to 20 nanometers across, with the optimal size was seven to 12 nanometers.
Once the crystals are formed in the solvent, they can be “painted” onto any surface. In a solar cell, the nanocrystals would be the layer that absorbs the sunlight and transfers that energy to electrons.
CZTS semiconductors can do a lot more, though. If they are small enough they CZTS can be “tuned” to emit different frequencies of light, depending on the current run through them.
The research will appear in the June 1 issue of the Journal of Crystal Growth.
Image: Lee J. Siegel / University of Utah