The researchers said their new discovery could open the way to the production of simpler solar panels made from a single material.
Researchers from the University of Cambridge in the United Kingdom claim to have discovered photovoltaic properties in a glowing organic semiconductor molecule known as poly(3-triphenylmethyl-thiophene (P3TTM).
Unlike conventional organic semiconductors, which have paired electrons, organic radical semiconductors contain at least one unpaired electron per molecule, giving them an ‘open shell’ character.
“In most organic materials, electrons are coupled and do not interact with their neighbors,” says lead author Biwen Li. “But in our system, when the molecules pack together, the interaction between the unpaired electrons at adjacent locations encourages them to alternately move up and down – a hallmark of Mott-Hubbard behavior.”
Mott-Hubbard behavior occurs in materials where electron-electron interactions are particularly strong. In P3TTM, each molecule can be viewed as a house containing a single electron. When light excites an electron, it can jump to a neighboring molecule. “When absorbing light, one of these electrons moves toward its nearest neighbor, creating positive and negative charges that can be harvested as photocurrent,” the team explained.
To test this, the researchers fabricated an experimental solar cell using a P3TTM film. The device contains a PEDOT:PSS layer on indium tin oxide (ITO), a buckminsterfullerene (C60) layer, a phenyl-C61-butyric acid methyl ester (PCBM) spacer and an aluminum (Al) contact.
Under standard lighting, the solar cell achieved near unity charge collection efficiency, the team reported.
“This means that almost every photon of light was converted into a useful electrical charge,” the researchers said. “In conventional molecular semiconductor solar cells, photon-to-charge conversion typically only occurs at interfaces between two materials – one acting as an electron donor and the other as an acceptor – limiting overall efficiency.”
“In these new materials, on the other hand, after photon absorption, the energy drives an electron from one molecule to an identical neighbor, creating electric charges,” she added. “The energy required for this – known as the ‘Hubbard U’ – represents the electrostatic cost of double electron occupancy on the negatively charged molecule.”
The researchers emphasized that this breakthrough could enable the manufacturing of solar cells from a single, cheap, lightweight material.
Their findings are available in the study “Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors”, published in natural materials.
“This work provides an opportunity for the exploration of energy generation and solar-powered chemistry in both solution and solid states using only a single component,” they concluded.
Their findings are available in “Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors”, published in natural materials.
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