Researchers nuke up new solar cell material in microwave that used to make lunch

A small, prototype solar cell that uses CZTS, a photovoltaic semiconductor that University of Utah metallurgists produced in an old microwave oven that once heated student lunches.
© Lee J. Siegel, University of Utah

What's cooking at the lab of Michael Free, a professor of metallurgical engineering, and Prashant Sarswat, a research associate in metallurgical engineering, at the University of Utah?

CZST semiconductors: just add copper, zinc, tin and sulfur to solvent, and nuke for 18 minutes. (But don't try this at home. These materials require special precautions.) According to the U. Utah press release:

Sarswat decided to try microwave production of CZTS when the University of Utah’s Department of Metallurgical Engineering decided to get a new microwave oven for the kitchen where students heat up their lunches and make coffee.

The team used the CZTS nanocrystal "ink" that results to build a photovoltaic solar cell (pictured) to "confirm that the material works and demonstrate that smaller nanocrystals display “quantum confinement,” a property that makes them versatile for different uses."

That table-tennis paddle thing in the center is a single nanocrystal of CZTS

The crystals Free and Sarswat cooked up are free of the more toxic metals like cadmium and arsenic, and are much cheaper and more available than the rare metals such as indium and gallium. In research published in the June 1 issue of the Journal of Crystal Growth, Sarswat reports on how the microwave process avoids unwanted side reactions and efficiently achieves uniform crystals of CZTS, a quaternary chalcogenide also known as "p-type photovoltaic absorber".

CZTS has been known since 1967 and was found suitable for photovoltaic material in 1998. Originally, a multi-step process required four to five hours to create a thin film of the crystals. This process was improved upon by a "colloidal synthesis" method, which could produce crystals in less than an hour and a half.

Solar cells using the CZTS technology reached a record 11.1% efficiency late last year. That may not seem like a lot compared to some solar efficiency breakthroughs, but if a solar technology can be made cheaply enough, efficiency need not be the highest.

Scientists Sarswat and Free

Sarswat and Free were beaten to publication by a team of researchers at Oregon State University, but filed an invention disclosure before the Oregon group, which will give them good cards if this process makes it to commercialization.

Researchers nuke up new solar cell material in microwave that used to make lunch
Scientists up-cycle the microwave that used to make lunch to develop a cheap method using more abundant and less toxic materials to make nanocrystal semiconductors.

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