Organic Solar Cells Could Receive Big Boost By Regulating Electron Spin, Research Finds

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Organic solar cells could receive a big boost to their efficiency through the manipulation of the “spin” of the electrons that they generate, according to new research from the University of Cambridge and the University of Washington.

Organic solar cells are a relatively new class of solar cell that works by mimicking the natural process of plant photosynthesis. They have a number of notable advantages over conventional photovoltaics, but current designs simply don’t possess the efficiency necessary to directly compete with commercial silicon solar cells. As it currently stands, organic solar cells max out at efficiencies of around 10-12%, while silicon-based cells max out at about 20-25%. A substantial difference.

But now, researchers have discovered a means of greatly improving organic solar cells — by manipulating the “spin” of the electrons in the solar cells, their performance can be greatly increased. The researchers think that this is “a vital breakthrough in the pursuit of cheap, high performing solar power technologies.”

"This is the laser set-up used to to make the actual measurements reported in the paper." Image Credit: Dr Akshay Rao

The University of Cambridge has details and background:

Organic solar cells replicate photosynthesis using large, carbon-based molecules to harvest sunlight instead of the inorganic semiconductors used in commercial, silicon-based solar cells. These organic cells can be very thin, light and highly flexible, as well as printed from inks similar to newspapers — allowing for much faster and cheaper production processes than current solar cells.

But consistency has been a major issue. Scientists have, until now, struggled to understand why some of the molecules worked unexpectedly well, while others perform indifferently.

Researchers from Cambridge’s Cavendish Laboratory developed sensitive laser-based techniques to track the motion and interaction of electrons in these cells. To their surprise, the team found that the performance differences between materials could be attributed to the quantum property of ‘spin’.

‘Spin’ is a property of particles related to their angular momentum, with electrons coming in two flavours, ‘spin-up’ or ‘spin-down’. Electrons in solar cells can be lost through a process called ‘recombination’, where electrons lose their energy — or “excitation” state — and fall back into an empty state known as the “hole”.

What the researchers then discovered was that, by organizing the electrons spin in certain ways, the energy collapse from “recombination” could be completely blocked, and thereby notably increase the current coming from the cell.

“This discovery is very exciting, as we can now harness spin physics to improve solar cells, something we had previously not thought possible. We should see new materials and solar cells that make use of this very soon,” stated Dr Akshay Rao, a Research Fellow at the Cavendish Laboratory and Corpus Christi College, Cambridge, who led the study with colleagues Philip Chow and Dr Simon Gélinas.

The researchers think that, in addition to the obvious applications in the solar energy field, the new findings and design concepts that have come out of their work could also be applied to Organic Light Emitting diodes, potentially leading to more energy-efficient displays for cell phones, tablets, TVs, etc.

The new findings were just published in the journal Nature.

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James Ayre

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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