University of Cambridge research has found that the atomic structure of organic solar material is able to generate electron activity in the same way as man-made crystalline solar cells, a discovery that could lead to cheap production of solar energy.
Scientists used an ultrafast camera to observe a phenomenon called “coherence”, which describes the behaviour of charged electrons as light is absorbed by photosensitive nanostructures. This phenomenon is not yet clearly understood by scientists and was previously thought to occur only in so-called “perfect” inorganic structures like the silicon crystals that form conventional solar cells, which require large amounts of heat and pressure to manufacture.
“This is a very surprising result. Such quantum phenomena are usually confined to perfect crystals of inorganic semiconductors, and one does not expect to see such effects in organic molecules – which are very disordered and tend to resemble a plate of cooked spaghetti rather than a crystal,” said Dr Simon Gélinas, from Cambridge’s Cavendish Laboratory.
The Cambridge team found that in the first femtosecond (one millionth of one billionth of a second) following the absorption of light into an artificially created organic nanostructure, the charge created spread rapidly over multiple molecules rather than being localised to a single one, due to the wavelike nature of electrons, a law of quantum mechanics known as spatial coherence.
Coherence allows a charge to travel quickly over a relatively large distance in atomic terms, and split from its oppositely charged partner which, in turn, can create long-term charges – the key to efficient energy generation.
The researchers found they were able to tune this coherence, thus amplifying or reducing the charge observed, by arranging different molecule patterns within the organic nanostructure.
“Perhaps most importantly the results suggest that because the process is so fast it is also energy efficient, which could result in more energy out of the solar cell,” said Dr Akshay Rao, a co-author on the study from the Cavendish Laboratory.
Results of the study have been published in the journal Science, and researchers believe the quantum processes involved could bring organic solar power a step closer to mimicking the photosynthesis, the highly efficient ability of plants to convert sunlight into energy.
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