Scientists have discovered that electrons can be propelled across solar materials at speeds close to the fastest nature allows, a result that challenges long accepted ideas about how solar energy systems operate.
The finding could open new paths for designing technologies that capture sunlight more efficiently and convert it into electricity.
In laboratory experiments tracking events lasting just 18 femtoseconds — less than 20 quadrillionths of a second — researchers at the University of Cambridge observed electric charge separating during a single molecular vibration.
“We deliberately designed a system that, according to conventional theory, should not have transferred charge this fast,” said Dr. Pratyush Ghosh, Research Fellow, at St John’s College, Cambridge, and first author of the study. “By conventional design rules, this system should have been slow and that’s what makes the result so striking.
“Instead of drifting randomly, the electron is launched in one coherent burst. The vibration acts like a molecular catapult. The vibrations don’t just accompany the process, they actively drive it.”
Watching Electrons Move on the Timescale of Atoms
A femtosecond is one quadrillionth of a second — one second holds about eight times more femtoseconds than all the hours that have passed since the universe began. At this incredibly small timescale, atoms inside molecules are constantly vibrating.
The researchers observed electrons moving between materials at essentially the same pace as those atomic motions. As Ghosh explained, “We’re effectively watching electrons migrate on the same clock as the atoms themselves.”
The research, published in Nature Communications March 5, 2026, challenges long standing design assumptions in solar energy science. Until now, scientists generally believed that ultrafast charge transfer required large energy differences between materials and strong electronic coupling. Those conditions can reduce efficiency by limiting voltage and increasing energy loss.
How Light Creates Energy in Solar Materials
When light strikes many carbon based materials, it creates a tightly bound packet of energy called an exciton — a paired electron and hole. For devices such as solar cells, photodetectors and photocatalytic systems to function effectively, this pair must separate quickly into free charges.
The faster the split occurs, the less energy is wasted. This ultrafast separation plays a critical role in determining how efficiently solar panels and other light harvesting technologies convert sunlight into usable power.
To investigate whether this trade off was unavoidable, the Cambridge researchers intentionally created what they expected to be a poorly performing system. They placed a polymer donor next to a non fullerene acceptor with almost no energy difference and only weak interaction — conditions that should have significantly slowed charge transfer.
Instead, the electron crossed the interface in just 18 femtoseconds. That speed is faster than many previously studied organic systems and matches the natural rhythm of atomic motion. “Seeing it happen on this timescale within a single molecular vibration is extraordinary,” said Dr. Ghosh.
Molecular Vibrations Drive Ultrafast Electron Motion
Ultrafast laser experiments helped reveal the mechanism behind this unexpected result. When the polymer absorbs light, it begins vibrating in specific high frequency patterns.
These vibrations mix electronic states and effectively push the electron across the boundary, creating a directional, ballistic motion instead of slow and random diffusion.
Once the electron reaches the acceptor molecule, it sets off a new coherent vibration. This distinctive signal is rarely observed in organic materials and indicates how quickly the transfer occurs. “That coherent vibration is a clear fingerprint of how fast and how cleanly the transfer occurs.
“Our results show that the ultimate speed of charge separation isn’t determined only by static electronic structure,” said Dr. Ghosh. “It depends on how molecules vibrate. That gives us a new design principle. In a way, this gives us a new rulebook. Instead of fighting molecular vibrations, we can learn how to use the right ones.”
Implications for Solar Energy and Light Harvesting
The discovery suggests a new strategy for designing more efficient light harvesting technologies. Ultrafast charge separation is fundamental to systems such as organic solar cells, photodetectors and photocatalytic devices that can produce clean hydrogen fuel. Similar processes also occur naturally during photosynthesis.
Professor Akshay Rao, Professor of Physics at the Cavendish Laboratory and former St John’s College Research Associate, who was a co author of the study, said: “Instead of trying to suppress molecular motion, we can now design materials that use it — turning vibrations from a limitation into a tool.”
The project involved scientists from the Cavendish Laboratory and the Yusuf Hamied Department of Chemistry at the University of Cambridge, including Dr. Rakesh Arul, St John’s College Research Fellow. Collaborators in Italy, Sweden, the United States, Poland and Belgium also contributed to the research.