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US Department of Energy Honors Northwestern Researchers for Solar Cell Breakthrough

Mike M. McMahon | August 7, 2019
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Transforming the way the world generates, stores, and uses energy has become a defining challenge of the century. In recognition of their contributions to developing transformative clean energy technologies, the US Department of Energy (DOE) recently honored Robert P.H. Chang and Mercouri Kanatzidis, two researchers from the Argonne Northwestern Solar Energy Research (ANSER) Center/Center for Light Energy Activated Redox Processes (LEAP) at the Institute for Sustainability and Energy at Northwestern (ISEN).

To mark the ten-year anniversary of its Energy Frontier Research Center (EFRC) program, DOE honored Chang and Kanatzidis—along with nine other teams of researchers from across the country—with the prestigious Ten at Ten Award. The award recognizes Chang and Kanatzidis for being the first to demonstrate an all-solid-state solar cell using halide perovskite materials. Members of Northwestern’s Center for Electrochemical Energy Science also received the award for unrelated work.

“I have been at Northwestern for over 30 years, and this is the first recognition of this kind that I’ve received from the Department of Energy, which feels very good,” says Chang, professor of materials science and engineering. “The fact that Northwestern was recognized reflects how university leadership is thoughtful in their hiring of qualified professors.”

Established in 2009 to bring together multi-disciplinary teams to tackle the toughest scientific challenges preventing advances in energy technologies, the EFRC program has involved more than 1,600 senior investigators and more than 5,400 students at some 170 institutions since its inception.

“The EFRC program is one of the most successful basic research initiatives I’ve seen in the country,” says Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry and (by courtesy) professor of materials science and engineering. “It nucleates a group of researchers that isn’t trivially small but also isn’t overly large to focus on a particular problem on a sustained basis. That has the maximum chance of having a big impact in the long term. The EFRCs publish a lot of papers and produce a lot of important breakthroughs. To get recognition like this from a place like the Department of Energy is a big deal.”

Collectively, the EFRCs have generated more than 11,600 peer-reviewed publications, more than 650 invention disclosures, and nearly 1,000 domestic and international patent applications.

The Breakthrough: Solid-state perovskite solar cells

Chang and Kanatzidis received the Ten at Ten Award for a scientific breakthrough that has led to a revolution in solar cell fabrication. The Northwestern team became the first to demonstrate an all-solid-state solar cell using halide perovskite materials in a milestone paper published in Nature in May of 2012.

Perovskites are a family of naturally occurring materials with similar molecular structures that allow for excellent light absorption, electrical conductivity, and durability. They are also low-cost and easily manipulated, making them a promising substitute for typical silicon-based solar cells. While initial applications of perovskite in solar cells occurred in 2006, were not very efficient (less than 4%) and were not stable since they relied on a liquid electrolyte. The inefficient cells had not captured much attention until Kanatzidis and Chang demonstrated solid-state versions in 2012.

“As you can image, if that liquid dries up, the solar cell becomes useless,” says Chang. “The challenge we faced was how to replace this liquid electrolyte with a solid form that would last much longer and potentially be more efficient.”

To solve this puzzle, Chang partnered with Kanatzidis, who had been studying the unique properties of perovskites since 2008. The serendipitous exchange between the two researchers is emblematic of the EFRC model.

“One day, professor Chang was presenting his research on dye-sensitized solar cells during the ANSER monthly meeting,” recounts Kanatzidis. “He was trying to figure out a way to create a dye-sensitized solar cell in a solid form instead of liquid without losing efficiency. He needed a material that was soluble and could be made into a film and conduct electricity in the right way. I approached him and explained the research my team was doing on perovskites. They were soluble, visible light absorbing, and conductive in the way he needed.”

“I’m an open-minded scientist, so I was willing to try anything,” adds Chang.

“Collaboration like this is the norm at Northwestern... [It] stimulates this kind of scientific discovery that you couldn’t have predicted at the outset. Everyone brings unique expertise that’s complementary.” — Professor Mercouri Kanatzidis, Northwestern University

The conversation between the two researchers sparked a revolution in perovskite solar cells. The team tested the materials in the lab, incrementally improving their formulas through trial and error. After 10 months, Chang and Kanatzidis had made history. They had developed a solid-state perovskite solar cell with 10% efficiency.

“When our research was published, it caught the scientific community by surprise, and people were very excited,” Chang says.

The breakthrough opened up new possibilities and opportunities for discovery. Within months of their publication, researchers in England, Japan, and Korea published similar findings.

“When I saw these publications, I knew we were at the start of a perovskite revolution. Everyone jumped in and started looking at this,” Kanatzidis says. “And it’s still early. Since our publication, efficiency has jumped up to 24%—the most rapid advance of any solar cell material in history.”

For comparison, the best silicon-based solar cells—which have been studied for decades—have recently reached just above 26% efficiency.

Both Chang and Kanatzidis attribute their success to the culture of interdisciplinary collaboration at Northwestern.

“Collaboration like this is the norm at Northwestern,” says Kanatzidis. “When I first arrived at Northwestern in the mid ‘80s… I came here so I could learn new fields. I was a chemist, but I wanted to learn physics and engineering. Those interactions were critical. Collaboration stimulates this kind of scientific discovery that you couldn’t have predicted at the outset. Everyone brings unique expertise that’s complementary.”

“My mode of operation is getting together with whomever has an idea,” Chang adds. “Working this way, we can all accomplish something that we couldn’t accomplish by ourselves.”

Kanatzidis is also the director of the Center for Advanced Materials for Energy and the Environment (CAMEE) at ISEN. The official Ten at Ten Award press release from DOE is available here.