Thin-film solar panels, cell phones, and LED light bulbs are all made using some of the rarest, most expensive elements found on the planet. An international team including researchers at Kalamazoo’s Western Michigan University and Ann Arbor’s University of Michigan have devised a way to make these kinds of optoelectronic materials from cheaper, more abundant elements.
Only specific kinds of compounds can be used to make electronic devices that efficiently emit light or gather electricity. The problem is, these compounds often involve elements that are only found in a few locations around the world.
“In fact, we’re in danger of running out of some of those elements because they’re not easy to recycle, and they’re in limited supply,” says Roy Clarke, a physicist who leads the U-M effort. “It’s not viable for technology to rely on something that’s likely to run out on a scale of 10 to 20 years.”
The research team found a way to combine two common elements to make a new compound. This new compound can be used in place of the rare elements and is far more abundant and less expensive. In addition, the new compound of zinc, tin, and nitrogen can harvest both solar energy and light. This means it would work in thin-film solar panels as well as in LED light bulbs, cell phone screens, and television displays. Using magnesium in place of zinc further extends the reach of the materials into blue and ultraviolet light.
Both compounds are also tuneable, meaning when the researchers grow crystals of either compound, the elements can be ordered in such a way that the material is sensitive to specific wavelengths of light. This tunability is desired because it allows researchers to tweak the material to respond to the widest range of light wavelengths. This is especially important so that device designers can select the color of light produced.
“When you’re lighting a home or an office, you want to be able to adjust the warmth of the light, oftentimes mimicking natural sunlight,” says Clarke. “These new II-IV-V compounds would allow us to do that.”
Graduate students Robert Makin, Krystal York, and James Mathis grew the thin films in Steve Durbin’s lab. Durbin is professor of electrical and computer engineering at Western Michigan University.
Makin, who just earned his Ph.D. from Western Michigan University and is the lead author of the study, used a technique called molecular beam epitaxy to produce the desired compounds under the correct conditions to make films with a carefully controlled degree of atomic ordering.
Molecular beam epitaxy lays down each atomic layer of the compound in a systematic fashion, allowing the researchers to study the thin layers of the structure as they grow it. The next phase of the research calls for detailed studies of these materials’ electronic response as well as testing of various nanoscale architectures.
The research team also includes members from the Université de Lorraine in France and the University of Canterbury in New Zealand. Their research is published in Physical Review Letters.