Turning Birch Leaves Into Semiconductors

Photo by Vidar Nordli-Mathisen

Physicists at Umeå University, in collaboration with researchers in Denmark and China, have discovered a sustainable way to produce semiconductors for optoelectronics like organic LEDs. Rather than using petrochemicals and rare metals like platinum and iridium, they pressure-cooked birch leaves picked on campus into nano-sized carbon particles with desired optical properties. Their research was published today in Green Chemistry.

“The heart of our work is harnessing nearby renewable resources to produce organic semiconductor materials,” said Jia Wang, a research fellow in the physics department at Umeå and an author of the study.

Organic semiconductors are crucial for optoelectronic applications like OLEDs, which enable the ultra-thin, vivid displays in TVs and phones. Skyrocketing demand for such advanced technologies is driving massive production of these semiconductors. Unfortunately, most are currently made from petrochemicals and rare elements obtained through environmentally harmful mining. They often contain “critical raw materials” like platinum, indium and phosphorus that are in short supply.

Ideally, scientists say, biomass from plants, animals and waste could produce organic semiconductors sustainably. These materials are renewable and abundant. Dr. Wang and her colleagues have succeeded in creating such a bio-based semiconductor.

Their simple process: picking birch leaves on campus and pressure cooking them. This yielded carbon dots around 2 nanometers wide that emit a narrow-band deep red light in ethanol. Though tiny, these “birch leaf carbon dots” have optical properties comparable to commercial quantum dots now used in semiconductors, but without heavy metals or critical raw materials.

“Our method works for various plant leaves,” Dr. Wang explained. “We tested many, and all produced similar red-emitting carbon dots. This versatility means the process could be used in different locations.”

In a light-emitting device using the carbon dots, the team achieved brightness of 100 cd/m2, like a computer screen.

“This shows it’s possible to shift from depleting petrochemicals to regenerating biomass for organic semiconductors,” said Dr. Wang.

Beyond light-emitting gadgets, she noted carbon dots’ broader potential for bioimaging, sensing, anti-counterfeiting and more. “We welcome collaborations to explore these emissive, sustainable carbon dots,” she said.

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