Molecular “catapult” discovery could transform solar energy technology

Scientists at the University of Cambridge have revealed a new mechanism that allows electrons to move across solar materials at extraordinary speeds, potentially reshaping how future solar technologies are designed

The discovery reveals that molecular vibrations can actively propel electrons across material interfaces, enabling faster charge transfer than previously believed possible.

The research, conducted by scientists at the Cavendish Laboratory and the Yusuf Hamied Department of Chemistry, shows that electrons can cross the boundary between two materials in just 18 femtoseconds.

This timescale indicates that the motion occurs within a single molecular vibration, suggesting a new pathway to improve light-harvesting technologies such as solar cells and photodetectors.

Breaking the rules of solar material design

Scientists have long believed that ultrafast charge transfer in solar materials requires strong electronic interactions and significant energy differences between the device’s components.

While these conditions help electrons move quickly, they also come with drawbacks, including energy loss and reduced electrical voltage.

The Cambridge team wanted to challenge this assumption by deliberately designing a system that should have been inefficient under traditional design rules.

They placed a polymer donor material next to a non-fullerene acceptor with very little energy difference between them and minimal electronic coupling. Conventional theory predicted that electron transfer in such a system would be slow.

Instead, the opposite occurred. Experiments revealed that electrons crossed the interface between the materials almost instantly, at speeds comparable to the natural vibrations of the molecules.

The role of molecular vibrations

The key to this unexpected speed lies in how molecules move. At extremely small timescales, atoms inside molecules vibrate continuously. In the Cambridge experiments, when light was absorbed by the polymer, these vibrations played an active role in driving electron motion.

Rather than diffusing randomly, the electron was propelled across the boundary in a rapid, directed burst. Scientists likened this behaviour to a molecular catapult, where vibrations effectively launch the electron from one material into another.

This vibration-driven motion also produced a distinctive signal when the electron reached the acceptor molecule. The arrival triggered a new coherent vibration in the receiving material. This vibration is rarely observed in organic systems and is a strong indicator of extremely rapid charge transfer.

Capturing events lasting only femtoseconds

To observe these ultrafast processes, the researchers used advanced laser techniques capable of measuring events on the femtosecond timescale. A femtosecond is one quadrillionth of a second, meaning that a single second contains vastly more femtoseconds than the total number of hours since the universe began.

With such tiny intervals, scientists can directly observe the interplay between electronic motion and atomic movement. The experiments showed that electron migration occurs on the same “clock” as the molecular vibrations themselves.

A new approach to designing solar materials

This discovery suggests that the ultimate speed of charge separation is not determined only by the static electronic structure of materials. It can be strongly influenced by how molecules vibrate after absorbing light.

This insight opens the door to a new design strategy for future solar energy systems. Rather than trying to suppress molecular motion, which has always been considered a source of inefficiency, researchers may be able to engineer materials whose vibrations actively assist electron transfer.

This approach could lead to more efficient organic solar cells, improved photodetectors and more effective photocatalytic systems used in clean-energy technologies such as hydrogen production. The findings also provide new insights into similar processes that occur in natural photosynthesis.

By demonstrating that molecular motion can drive ultrafast electron transfer, the study introduces a new framework for designing next-generation light-harvesting materials.