Advancing Solar Science

Creating and storing solar power is increasingly important as the United States moves toward its goal of net-zero carbon emissions by 2050. Erin Ratcliff, a University of Arizona associate professor of chemical and environmental engineering and chemistry and biochemistry, is leading one of the U.S. Department of Energy’s Energy Frontier Research Centers to advance energy conversion and storage technologies using soft organic polymer electronic materials.

Funded at $10.95 million over four years, the UArizona-based Center for Soft PhotoElectroChemical Systems, or SPECS, will focus on the molecular-level science behind low-cost, highly scalable soft semiconductor technologies. These semiconductors will absorb light, create electricity and use the electricity to drive electrochemical reactions and create chemicals called solar fuels — a sustainable alternative to fossil fuels and batteries. A prime example is hydrogen produced from sunlight.

Energy Frontier Research Centers, or EFRCs, bring together interdisciplinary teams to tackle the toughest scientific advances in energy technologies. This year, the Department of Energy awarded more than $400 million to establish and continue 43 EFRCs.

“Leading an EFRC is an outstanding achievement for faculty members at any stage in their careers, but this is particularly notable because Erin Ratcliff, who began at the university as a postdoc, is an associate professor,” says David W. Hahn, the Craig M. Berge Dean of the College of Engineering. 

“Erin is an excellent researcher with a knack for bringing together experts from different disciplines, backgrounds and career stages to solve grand challenges related to sustainable energy. Her approach to science and engineering is perfectly aligned with the EFRC program.”

Durability and ‘exquisite control’

Most current energy storage and solar fuel-formation technologies are made of hard, inorganic materials. But those materials are increasingly costly and difficult to acquire. They also are difficult to scale, especially to the levels needed to achieve a carbon-free energy economy by 2050. At the molecular level, converting solar energy to electrical energy — and sometimes storing that energy for later use — involves a series of redox reactions, or electron exchanges between molecules.

SPECS will focus on using organic polymers: long chains of molecules that interact with one another at many points. Unlike traditional, inorganic devices, which are formed by attaching individual atoms, the multitude of interacting points in organic polymers increases reliability by providing more potential pathways for a chemical reaction to follow. 

Ratcliff says one analogy compares a network of polymers to a bowl of spaghetti, in which the strands overlap at many points. Even if the spaghetti shifts and one possible communication path is no longer an option, many other paths are still available.

“If you have a molecule and you break one bond, that molecule is now a completely different molecule, with new properties, new colors, new energy levels, new electrochemistry,” Ratcliff says. “But with polymers, you can break one bond and it can be possible to still do everything you need it to do.”

The tunability provided by synthesis and processing, combined with the multitude of pathways in polymers, gives researchers what Ratcliff calls “exquisite control” over the polymers’ properties — the ability, in short, to recalibrate the materials to work exactly as needed under different conditions. It also means the polymers can adjust themselves dynamically to maintain equilibrium — for example, swelling and relaxing as temperatures change.

The SPECS team is focused on a specific class of polymeric materials that contain alternating single and double bonds between molecules and are able to conduct electricity. Their chemical structure makes these polymers especially scalable and durable. To learn about and advance the properties of these materials, the team will develop new measurement approaches. Its findings will help advance the field of fundamental semiconductor science regardless of the project’s outcomes.

A journey comes full circle

The center has been years in the making for Ratcliff, who began her UArizona postdoctoral research in chemistry and biochemistry in 2007. When her adviser — Neal Armstrong, a Regents Professor of chemistry and biochemistry and optical sciences — began leading his own EFRC in 2009, he selected Ratcliff as the research scientist in the Center for Interface Science: Solar Electronic Materials. In this position, she coordinated efforts between center members across the country and received national recognition from the U.S. Department of Energy for her work. 

Along the way, she learned about EFRC best practices. “That includes the management and budget considerations, but also the nitty-gritty aspects of team science: keeping everyone engaged and happy and having to make hard decisions — but also learning how to empower everyone, especially the younger group,” says Ratcliff, now director of the university’s Laboratory for Interface Science of Printable Electronic Materials. “I’ve wanted to lead an EFRC since back in 2009. I love team science, and I’m really excited about my team. I hand-picked every single one of them.”

SPECS includes experts in photovoltaics and photoelectric chemistry at the University of Colorado-Boulder, National Renewable Energy Laboratory, Georgia Institute of Technology, University of Kentucky, Emory University, Purdue University and Stanford University. The other UArizona faculty members on the team are Jean-Luc Brédas, Regents Professor of chemistry and biochemistry, and Adam Printz, assistant professor of chemical and environmental engineering. Ratcliff selected people who bring not only a wide range of expertise but also varying experience levels and diverse backgrounds.

“If you look at the composition of that group, it is pretty jaw-dropping,” says Armstrong, now a senior adviser for SPECS. “She got everyone excited, and that was necessary since this is really high impact and high risk, which is exactly what these programs are about. 

“This is a big win for her, for the University of Arizona and its students, for the U.S., and for the DOE.”