In a discovery spanning over a century of physics, researchers at the University of Cambridge have achieved a groundbreaking scientific breakthrough that could significantly simplify and reduce the cost of solar energy production. The team has observed a complex quantum phenomenon, previously thought to exist only in exotic inorganic materials, thriving within a simple, light-harvesting organic semiconductor molecule.

The research was published in Nature Materials.

The study’s foundation is a spin-radical organic semiconductor molecule called P3TTM. Unlike conventional materials, where electrons are paired, P3TTM contains a single, unpaired electron at its core, giving it unique magnetic and electronic properties.

This work is a collaboration between the synthetic chemistry team of Professor Hugo Bronstein in the Yusuf Hamied Department of Chemistry and the semiconductor physics team led by Professor Sir Richard Friend in the Department of Physics.

A Single, Organic Material Could Redefine Solar Energy

The team’s critical finding is that when these molecules are packed closely together, their unpaired electrons interact in a manner strikingly similar to a Mott-Hubbard insulator. This is the key to creating electricity from a single material.

“This is the real magic. In most organic materials, electrons are paired up and don’t interact with their neighbors,” said Biwen Li, the lead researcher at the Cavendish Laboratory. “But in our system, when the molecules pack together, the interaction between the unpaired electrons on neighbouring sites encourages them to align themselves alternately up and down, a hallmark of Mott-Hubbard behaviour.”

Li added, “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).”

This is fundamentally different from conventional molecular solar cells, which require an interface between an electron donor and an electron acceptor to convert light into usable charge. In contrast, the P3TTM film demonstrated a remarkable close-to-unity charge collection efficiency, meaning almost every photon of light was converted into electricity by the single material itself.

Dr. Petri Murto, in the Yusuf Hamied Department of Chemistry, developed the molecular structures that enabled the precise tuning of this Mott-Hubbard physics necessary for charge separation. This success suggests that solar cells could soon be fabricated from a single, low-cost, and lightweight material.

Ultimately, the Cambridge research team believes this is more than just an incremental improvement. Professor Bronstein said, “We are not just improving old designs. We are writing a new chapter in the textbook, showing that organic materials are able to generate charges all by themselves.”