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At the University of Kansas, researchers have made an exciting breakthrough in the field of organic semiconductors, which may make way for a new era for solar cells. Silicon, prized for its efficiency and durability, has been the king of solar energy for years, but its rigidity and high production costs limit its use on curved surfaces, holding back innovation.
Enter organic semiconductors: carbon-based materials that offer a flexible and affordable alternative. According to Wai-Lun Chan, associate professor of physics & astronomy at the University of Kansas, in solution-based methods, they can even be coated on arbitrary surfaces, allowing solar panels to be applied like paint on a wall. He explains that this could drastically reduce production costs, while also enabling creative designs for buildings, such as transparent or colored solar panels blending in with the architecture.
Despite their promise, organic solar cells have been unable to keep up with silicon, in general achieving only around 12% efficiency compared to silicon’s impressive 25%. But hope is on the horizon. The introduction of materials called non-fullerene acceptors (NFAs) has pushed organic cell efficiency closer to 20%, significantly narrowing the gap.
Curious about this leap in performance, the research team set out to uncover the secret behind NFAs. To their surprise, they discovered that excited electrons in NFAs can actually gain energy from their surroundings rather than lose it, defying traditional expectations. This was revealed through an advanced technique called time-resolved two-photon photoemission spectroscopy, that allowed them to track energy of excited electrons in real-time.
The researchers believe this phenomenon is linked to quantum mechanics and thermodynamics. At the quantum level, excited electrons can seem to exist on multiple molecules at once, and along with the second law of thermodynamics, this can reverse the direction of heat flow.
In the press release, graduate student Kushal Rijal explained: “For organic molecules arranged in a specific nanoscale structure, the typical direction of the heat flow is reversed for the total entropy to increase. This reversed heat flow allows neutral excitons to gain heat from the environment and dissociate into a pair of positive and negative charges. These free charges can in turn produce electrical current.”
With these findings, the future of solar energy looks brighter and more versatile than ever.
