Made of non-toxic, inexpensive elements, chalcogenide perovskites can be used in lighting, solar cells, and other applications.
MIT engineers have created the first thin films of a new class of semiconductor materials. Rafael Jaramillo, the lead researcher, refers to the feat as his “white whale” due to his obsessive pursuit of it over the years. It can impact multiple fields of technology if history repeats itself. High-quality films made from other semiconductor families led to computers, night-vision cameras, and solar cells.
Jaramillo, Thomas Lord Associate Professor in Materials Science and Engineering at MIT, says that when introducing new material to the market, “the greatest scientific breakthroughs can only be made when we have access to the best materials available.” Low-quality materials can often be a false negative in terms of their scientific value and technological potential.
Jaramillo suggests that the new family of semiconductors, chalcogenide-perovskites, could be used in lighting and solar cells. Jaramillo notes that the history of semiconductor research has shown that new semiconductor families are generally more enabling than expected.
Jaramillo is excited by the potential of these new materials because they are stable and made from non-toxic, inexpensive elements. Jaramillo explains that his team’s thin films are composed of barium and zirconium in a crystal structure called “the prototypical Chalcogenide Perovskite.” You can create variations by changing the composition. It is a collection of materials and not a single one.
The article was published in the Advanced Functional Materials issue on November 3, 2021. Jaramillo’s coauthors include Ida Sadeghi (a postdoctoral researcher in the Department of Materials Science and Engineering, DMSE) and the first author of this paper. Kevin Ye, Michael Xu, and Yifei LI are all DMSE graduate students; James M. LeBeau is the John Chipman Associate Professor of Materials Science and Engineering at MIT.
A little history
French chemists created chalcogenide perovskites as early as the 1950s. Jaramillo states that similar work was done in the 80s and early 90s, and “the idea of these materials being useful semiconductors wasn’t coming up until the early 2010s.” Jaramillo, Jayakanth Ravichandran, and Joseph Bennett were all postdocs at that time and independently discovered their potential.
Today, Bennett and Ravichandran are professors at the University of Southern California and the University of Maryland Baltimore County, respectively. Jaramillo considers them to be friends. Jaramillo first met Ravichandran while they were both postdocs at Harvard University. He has continued to pursue the goal of producing high-quality chalcogenide films using a different approach. Ravichandran continues to be a success in this area.
How they did it
Jaramillo and his colleagues used molecular beam epitaxy to produce their high-quality films. Jaramillo states that although the technique can be controlled at the atomic level over crystal growth, it is not easy to use and only guarantees success with new material. However, the history of semiconductor technology has shown the importance of MBE. It’s worth trying.
MBE, as its name suggests, aims beams of molecules at specific arrangements of atoms on a surface (“taxi”), which is epitaxy for account or orientation. This arrangement of atoms is a template that the beam molecules can use to grow on. “Epitaxial growth is the best way to make high-quality films. Jaramillo states that the materials can grow.
Another factor added to the difficulty was that “chalcogenides require nasty chemicals.” Jaramillo said that they stink and can clog up equipment. MBE is held in a vacuum chamber. Jaramillo recalls people’s reluctance to give his group access to the rooms.
Hideo Hosono is a Tokyo Institute of Technology professor who wasn’t involved in the research. “The thin films [created by Jaramillo et.],” says Hideo. The mirror-smooth appearance is due to the excellent quality and atomically flat surface. In the following publication, we may see the realization of device fabrication, like solar cells or green LEDs.
What’s next?
Jaramillo states that it’s almost impossible to know what’s next. Jaramillo says, “Now that we can make this high-quality material, there is almost no measurement that would not be interesting to an extensive community of people.” His group is currently focusing on two areas. They will investigate fundamental questions to better understand and integrate the materials into solar cells. Jaramillo was a postdoctoral researcher before joining the MIT faculty. He worked on solar cells, so “I’ll have the ability to leverage a lot from what I did back then.”
Jaramillo’s lab at MIT focuses on more than just chalcogenide perovskites. “But this project is certainly the one we are most proud of because it took the most effort and has the longest delayed gratification.”