The study reveals that a specially designed organic semiconductor, known as P3TTM, can replicate a physical phenomenon previously observed only in inorganic metal oxides. This finding unites principles from both organic chemistry and condensed matter physics, offering a simpler, lighter, and more affordable route to solar power generation.
P3TTM is a spin-radical organic molecule containing a single unpaired electron at its core. Developed through collaboration between Professor Hugo Bronstein's synthetic chemistry group and Professor Sir Richard Friend's semiconductor physics team, the material was initially designed for use in organic LEDs. However, new research published in Nature Materials uncovered a hidden property: when closely packed, P3TTM molecules exhibit electronic interactions similar to those found in a Mott-Hubbard insulator.
"In most organic materials, electrons exist in pairs and remain isolated," explained Biwen Li from the Cavendish Laboratory. "In P3TTM, neighboring unpaired electrons interact and align alternately up and down. When light hits the material, one of these electrons hops to its neighbor, generating positive and negative charges that can be extracted as electrical current."
When configured as a solar cell, a thin P3TTM film achieved an almost perfect charge collection efficiency - meaning nearly every photon of light was converted into usable electricity. Unlike traditional organic solar cells that require two materials to transfer electrons and holes, P3TTM can generate charge separation internally, driven by its intrinsic electronic structure governed by Mott-Hubbard physics.
Dr. Petri Murto designed molecular structures that fine-tune the energy balance between molecules, enabling efficient charge separation. This single-material solar cell concept could drastically reduce manufacturing complexity and costs while improving performance.
The discovery also carries symbolic weight. Senior author Professor Sir Richard Friend studied under Sir Nevill Mott, whose pioneering theories of electron interaction underpin this new breakthrough. "It feels like coming full circle," said Friend. "To see Mott's ideas realized in a modern organic system that can turn light into electricity is truly special."
Professor Hugo Bronstein added, "We are not just improving old designs. We are writing a new chapter in the textbook, showing that organic materials can generate charge entirely on their own."
Research Report:Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors
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