Study Finds Light-Driven Chemistry Boosts Electronic Properties of Polymers
In a Science Advances study, Dr. Wei You, senior author and professor of chemistry and applied physical studies, uses light to trigger the doping process with materials that are stable in air and easy to handle.
June 11, 2025 I By Dave DeFusco
Imagine charging your phone with a solar panel built into your backpack, or wearing a shirt that powers your fitness tracker. These kinds of futuristic, flexible electronics are becoming more possible thanks to new materials called organic semiconductors—plastics that can carry electrical currents like silicon, but are lighter, cheaper and can bend or stretch.
To make these materials work in devices like solar cells, OLED screens or sensors, scientists have to do something called “doping”—adding tiny amounts of other chemicals to help the plastic move electricity better. It’s like giving your car a turbo boost; it doesn’t change the engine, but it makes it run faster and more efficiently.
Until now, this doping process has been much easier to do on p-type plastics, which carry positive charges, than on n-type plastics which carry negative charges. That’s a problem, because to build real electronic circuits, both p-type and n-type materials are necessary, just like there are positive and negative ends on a battery.
In a Science Advances study, “Air Stable n-Type Dopant for Organic Semiconductors via Single Photon Catalytic Process,” a team of researchers from UNC-Chapel Hill, the University of Washington and NC State University has come up with a surprisingly simple and powerful solution: use light to trigger the doping process with materials that are stable in air and easy to handle.
“This method is like doping with a flashlight,” said Liang Yan, the paper’s lead author and a research assistant professor in the UNC Department of Chemistry. “We use a small amount of a light-sensitive chemical called acridinium, shine UV light on it and it transfers electrons in a way that ‘charges up’ the plastic.”
Dr. You said the 2020 Nature article, “Discovery and Characterization of an Acridine Radical Photoreductant,” authored by Dr. David Nicewicz, William R. Kenan, Jr. Distinguished Professor at UNC, inspired their idea of using the photoredox catalyst Mes-Acr to achieve n-type doping.
“Dave has made significant contributions in demonstrating the strength of the Mes-Acr photoredox catalyst,” said Dr. You, “paving the way for new discoveries in selective organic transformations and the broader development of sustainable synthetic methods. It was very cool that one Carolina chemist’s work inspired another Tarheel!”
What makes You and Yan’s breakthrough special is that it works with mild and safe ingredients—no dangerous or unstable chemicals needed—and it happens at room temperature. That’s a big deal in a field where n-type doping often involves harsh materials like lithium metal that react explosively with air.
The magic ingredient here is a photoredox catalyst—a molecule that stays stable in the dark, but turns into a powerful electron-mover when exposed to light. In this study, the researchers used Mes-Acr⁺, an acridinium salt that’s sold commercially and can be handled in open air. When mixed with a common amine—a mild base called DIPEA—and exposed to UV light, it can transfer electrons to a plastic called N2200, one of the most popular n-type organic semiconductors.
Put simply, this method:
- Requires only light, air-stable chemicals and plastic
- Takes place at room temperature, not in dangerous conditions
- Produces high conductivity, meaning it helps plastics carry electricity as well as the best current methods
- Works through a “one-photon-one-electron” process—a clean and efficient reaction sparked by a single flash of light
Dr. Wei You, senior author of the paper and professor of chemistry and applied physical sciences in the Department of Chemistry at UNC, said this innovation could “open the door to scalable, safe and flexible organic electronics.”
“The beauty of this method,” he said, “is in its simplicity. It’s easy to apply and adapt to many different kinds of plastic semiconductors. That’s going to make a huge difference for researchers and engineers trying to build real devices.”
Here’s how it works:
- Spin-Coating the Plastic: The researchers made a thin film of N2200 plastic on a glass slide—about 1/1000th the thickness of a human hair.
- Light Dipping: They dipped this film into a liquid containing the acridinium and amine, and shined UV light on it for about 30 minutes.
- Electrical Boost: After drying the film, they measured how well it carried electricity. With all three parts—light, acridinium and amine—it showed a huge jump in conductivity. Without even one of those, the boost didn’t happen.
- Proving the Science: They used special tools like electron paramagnetic resonance (EPR) and ultraviolet photoelectron spectroscopy (UPS) to confirm that the electrons had indeed moved into the plastic, creating the negatively charged particles, called polarons, that allow n-type conduction.
They even added a special ionic liquid to help the process along, and got conductivity numbers close to the best ever reported for this kind of plastic. This light-driven method doesn’t just work for one type of plastic. The researchers tested it on other common materials, including BBL, a ladder-shaped plastic used in sensors and transistors. The process worked there, too, showing its versatility and broad potential.
“We’ve only scratched the surface,” said Dr. Yan. “There are so many different plastics and photoredox catalysts we can try. We think this approach can work in all kinds of flexible electronics, especially where traditional doping methods fall short.”
This could make a real difference in solar panels that work in cloudy weather, wearable electronics that conform to your body and even electronic skin or paper-based displays. Now that the team has shown this method works, they hope to explore even more combinations of catalysts and plastics. They’re also studying how to apply the process in large-scale manufacturing, like roll-to-roll printing, where you can print electronics the way newspapers are printed.
“The future of electronics is soft, flexible and wearable,” said Dr. You. “And that future just got a little bit closer, thanks to this simple but powerful way to bring n-type plastics into the mix.”