The promise of organic materials for wearable and even disposable electronics is at the heart of new research by Rice University chemical engineer Rafael Verduzco, who has earned a coveted CAREER Award from the National Science Foundation.
Verduzco, an assistant professor of chemical and biomolecular engineering who earned his undergraduate degree at Rice in 2001 and joined the faculty in 2009, said the five-year grant is worth about $500,000. The grants go to young scientists who are expected to have significant impact on their fields of study.
Verduzco’s group at Rice is developing flexible organic solar cells that could be used in electronic applications and devices. While not as efficient as silicon-based solar cells, organics could significantly reduce the cost of solar energy for many applications, he said. In recent work, his lab produced a cell based on block copolymers, organic materials that arrange themselves into distinct nanoscale layers.
“These materials are cheaper than silicon,” he said. “They can be painted or inkjet-printed on a surface. Organic solar cells are not going to compete with current technology, but we believe there’s a new set of applications that will come about from their development.
“We can start to imagine combining solar cells with printable electronics on backpacks, on clothing, on windows and on things like disposable cups that would amount to self-powered displays. You would never imagine doing things like this with silicon solar cells.”
State-of-the-art organic solar cells have achieved about 10 percent efficiency; that is, they turn 10 percent of the incoming solar energy into electricity. (The most efficient silicon cells are at about 25 percent efficiency.) But their polymer/fullerene composition doesn’t take advantage of the order offered by block copolymers, Verduzco said. “Controlling the structure of electron and hole conductors at the nanoscale is hard to do with organic materials because they tend to be messy and disordered,” he said.
“But we like to think of our polymers as single molecular photovoltaic junctions. Half of one molecule is a hole conductor, half is an electron conductor, and we bind them together chemically so we can control the interface. How you connect them together is really important.
“They help us understand how nanoscale structures translate to electron conduction, light absorption and charge separation, all these steps in organic materials that are still kind of fuzzy, even after a couple of decades of studying these materials,” he said. “Theoretically, we should be able to do better than the efficiency of state-of-the-art polymer fullerene solar cells.
“Once we get to the point where it’s practical to make a lot of these cells, they’re going to find niche applications,” Verduzco said. “And if the efficiency progresses even further, we can imagine them competing with silicon for power generation, where the advantage of organics would be cost. Organics are very easy to scale up to large-area devices.”
— Mike Williams, Rice University Public Affairs