In a remarkable convergence of chemistry and quantum physics, researchers at the University of Cambridge have uncovered a light-harvesting phenomenon once thought unique to inorganic materials, thriving instead within a glowing organic semiconductor molecule. Credit: SciTechDaily.com
Cambridge scientists have uncovered a hidden quantum mechanism in an organic semiconductor that could revolutionize solar energy.
In a finding that connects modern research with ideas from a century ago, scientists have identified in an organic semiconductor a behavior that was long believed to occur only in inorganic metal oxides. The team led by the University of Cambridge reports a previously unrecognized way to convert light into electrical energy. This advance could reshape solar power and electronics by enabling lighter, cheaper, and simpler solar panels built from a single material.
The research centers on a spin-radical organic semiconductor called P3TTM. A single unpaired electron sits at its core and gives the molecule distinctive magnetic and electronic properties. The project combines the synthetic chemistry group of Professor Hugo Bronstein in the Yusuf Hamied Department of Chemistry with the semiconductor physics group led by Professor Sir Richard Friend in the Department of Physics.
They have developed this class of molecules to give very efficient luminescence, as exploited in organic LEDs, but the new study, published in Nature Materials, reveals their hidden talent: when brought into close contact, their unpaired electrons interact in a manner strikingly similar to a Mott-Hubbard insulator.
A thin film emits red light from radical doublet excited state. Credit: Biwen Li – Cavendish Laboratory, University of Cambridge
Quantum Interactions at Work
“This is the real magic,” explained Biwen Li, the lead researcher at the Cavendish Laboratory. “In most organic materials, electrons are paired up and don’t interact with their neighbors. But in our system, when the molecules pack together, the interaction between the unpaired electrons on neighboring sites encourages them to align themselves alternately up and down, a hallmark of Mott-Hubbard behavior. Upon absorbing light, one of these electrons hops onto its nearest neighbor, creating positive and negative charges which can be extracted to give a photocurrent (electricity).”
The team demonstrated this by creating a solar cell from a P3TTM film. When light hit the device, it achieved a remarkable close-to-unity charge collection efficiency, meaning almost every photon of light was converted into a usable electrical charge. In conventional molecular semiconductor solar cells, the conversion of an absorbed photon into electrons and holes (electricity) can only happen at the interface between two different materials where one acts an electron donor and the other as an electron acceptor, and this compromises overall efficiency.
Mott-Hubbard basic energy levels. Credit: Biwen Li – Cavendish Laboratory, University of Cambridge
In contrast, for these new materials, after a photon is absorbed, it is energetically “downhill” to move an electron from one molecule to an identical neighboring molecule, thus creating electrical charges. The energy required for this, often termed the “Hubbard U” is the electrostatic charging energy for double electron occupancy of the molecule that has become negatively charged.
Designing Molecules for Efficiency
Dr Petri Murto in the Yusuf Hamied Department of Chemistry developed molecular structures that allow tuning of the molecule-to-molecule contact and the energy balance governed by Mott-Hubbard physics needed to achieve charge separation. This breakthrough means that it might be possible to fabricate solar cells from a single, low-cost, lightweight material.
The discovery carries profound historical significance. The paper’s senior author, Professor Sir Richard Friend, interacted with Sir Nevill Mott early in his career. This finding emerges in the same year as the 120th anniversary of Mott’s birth, paying a fitting tribute to the legendary physicist whose work on electron interactions in disordered systems laid the groundwork for modern condensed matter physics.
“It feels like coming full circle,” said Prof. Friend. “Mott’s insights were foundational for my own career and for our understanding of semiconductors. To now see these profound quantum mechanical rules manifesting in a completely new class of organic materials, and to harness them for light harvesting, is truly special.”
“We are not just improving old designs,” said Prof. Bronstein. “We are writing a new chapter in the textbook, showing that organic materials are able to generate charges all by themselves.”
Reference: “Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors” by Biwen Li, Petri Murto, Rituparno Chowdhury, Laura Brown, Yutong Han, Giacomo Londi, David Beljonne, Hugo Bronstein and Richard H. Friend, 30 September 2025, Nature Materials.
DOI: 10.1038/s41563-025-02362-z
Funding: European Research Council
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