Mechanism from quantum mechanics is seen to reduce losses in internal energy transfer

Researchers at the University of Toronto have demonstrated how efficient solar cells based on organic polymers can become reality. "One of the greatest obstacles for organic solar cells has been that we could scarcely control what happened after light absorption," says Elisabetta Collini, chemist in Toronto. Together with her colleague Greg Scholes, she developed an approach to actually direct the energy transfer in conjugated polymers effectively. This promises a higher energy yield for organic solar cells.

Previous strong losses due to hopping in the transfer of absorbed energy

Conjugated polymers are long organic molecules that have been known as good candidates for implementing more efficient organic solar cells. One problem is that the absorption of light at the surface of a solar cell is only a first step on the path to current production. "The absorbed light must first travel to an interface, where it is transformed into usable positive and negative charges," describes Wichard J. D. Beenken, physicist at the Technical University of Illmenau. If this transfer along the polymer chain occurs in hops via repeated absorption and reemission, this is not really effective. Each such hop means a drop in energy and thus reduces the achievable voltage, while the probability of random radiation rises and negatively affects the amount of current.

In their experiments, the scientists in Toronto demonstrated a different transfer mechanism. "We found that the ultrafast movement of energy through and between molecules happens by a quantum-mechanical mechanism rather than through random hopping, even at room temperature," describes Scholes. "This is extraordinary and will greatly influence future work in the field because everyone thought that these kinds of quantum effects could only operate in complex systems at very low temperatures," he said. The quantum state migrates only along individual molecule chains whose chemical structure Scholes sees as the significant factor for the quantum coherent energy transfer.

Faster, less loss, more effective

If the results of the research in Toronto can be transferred into practice, then according to Beenkens this would mean huge advantages particularly for solar cells. "This would be a continuous energy flow along a polymer", comments Beenken. This variant is faster and suffers less loss than the hopping behavior. The cumulative effectiveness is higher because there is no energy-consuming absorption and reemission, and the faster transfer also minimizes the risk of random radiation of the captured light. "This means higher voltage and current," says Beenken. Whether the technological implementation of the Canadian approach succeeds remains to be seen. To be effective, this requires the complete redesign of organic solar cells with respect to the arrangement of the polymer chains and the interface, says Beenken.

Source: Pressetext.at (translated)