Researchers at the University of Cambridge have observed electrons crossing boundaries in solar materials in just 18 femtoseconds, driven by molecular vibrations. This discovery challenges traditional theories on charge transfer in solar energy systems. The findings suggest new ways to design more efficient light-harvesting technologies.
Scientists at the University of Cambridge conducted experiments revealing that electrons can transfer across solar materials at speeds near the limit of natural processes. In tests lasting 18 femtoseconds—one quadrillionth of a second—researchers watched electric charge separate during a single molecular vibration. This ultrafast movement occurred in a system designed to perform poorly under conventional rules, featuring a polymer donor adjacent to a non-fullerene acceptor with minimal energy difference and weak interaction.
Dr. Pratyush Ghosh, a Research Fellow at St John's College, Cambridge and the study's first author, noted: "We deliberately designed a system that, according to conventional theory, should not have transferred charge this fast." He added that the electron launches in one coherent burst, with vibrations acting like a molecular catapult: "The vibrations don't just accompany the process, they actively drive it."
The observation aligns electrons' migration with atomic motions, as Ghosh explained: "We're effectively watching electrons migrate on the same clock as the atoms themselves." Ultrafast laser experiments showed that light absorption triggers high-frequency vibrations in the polymer, mixing electronic states and propelling the electron ballistically across the interface. Upon reaching the acceptor, it initiates a new coherent vibration, signaling the transfer's speed and cleanliness.
Published in Nature Communications on March 5, 2026, the research questions assumptions that ultrafast charge transfer requires large energy gaps and strong coupling, which often reduce efficiency. Ghosh stated: "Our results show that the ultimate speed of charge separation isn't determined only by static electronic structure. It depends on how molecules vibrate. That gives us a new design principle."
Professor Akshay Rao, from the Cavendish Laboratory, commented: "Instead of trying to suppress molecular motion, we can now design materials that use it—turning vibrations from a limitation into a tool."
The study involved collaborators from the University of Cambridge's Cavendish Laboratory and Yusuf Hamied Department of Chemistry, as well as teams in Italy, Sweden, the United States, Poland, and Belgium. This mechanism is key for organic solar cells, photodetectors, and photocatalytic devices that generate clean hydrogen fuel, mirroring processes in natural photosynthesis.
