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.
“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).”
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