Researchers at the University of Cambridge have discovered a previously unknown quantum mechanism in an organic semiconductor that could significantly enhance the capture and conversion of solar energy into electricity
The finding opens the door to next-generation solar technology that’s lighter, cheaper, and potentially more sustainable than current systems.
The research revisits theories first explored nearly a hundred years ago. Historically, a type of behaviour known as Mott-Hubbard physics was thought to occur only in complex inorganic materials, such as metal oxides. These systems are critical to understanding high-temperature superconductors and other quantum phenomena.
Now, for the first time, scientists have observed this same behaviour in a class of organic semiconductors. These are carbon-based materials more commonly used in flexible electronics and OLED screens. The discovery challenges the assumptions about how organic molecules behave when exposed to light and reveals untapped potential for solar energy applications.
Unpaired electrons
A significant aspect of this discovery is a specially designed molecule known as P3TTM, an organic semiconductor with a unique property: it contains a single unpaired electron, making it a spin-radical. Unlike most organic materials, where electrons are paired and relatively inert, the unpaired electrons in P3TTM interact strongly with their neighbours when the molecules are closely packed.
This interaction leads to a stable, repeating arrangement of up-and-down electron spins, hallmarks of Mott-Hubbard behaviour. When the material absorbs light, electrons can jump from one molecule to the next, leaving behind positive charges. This process, known as charge separation, enables the flow of electricity necessary for solar cell operation.
A single material for high efficiency
What makes this breakthrough especially exciting is that these interactions enable solar energy conversion using just one type of material. Traditional organic solar cells require two materials, one to donate electrons and another to accept them, which makes them more complex and less efficient.
The new P3TTM-based solar cell achieves an almost charge collection efficiency, meaning nearly every photon of light absorbed is converted into usable electrical energy. This is possible because the process of moving an electron to a neighbouring molecule is energetically favourable, requiring no external push or additional materials.
Engineering the perfect fit
To fine-tune this behaviour, researchers carefully engineered the structure of the molecules to optimise how they stack and interact. By adjusting how tightly the molecules pack and how easily electrons can move between them, the team created a material that not only absorbs light effectively but also conducts electricity with efficiency.
This design flexibility could lead to solar panels that are ultra-light, flexible, and easy to manufacture, making them ideal for applications ranging from portable electronics to building-integrated photovoltaics.
The theoretical framework behind the findings stems from the work of physicist Sir Nevill Mott, whose research into electron behaviour earned him a Nobel Prize. With 2025 marking the 120th anniversary of Mott’s birth, the team’s work serves as a timely tribute, connecting past theory with future technology.
