What could solar cells make more efficient?

More energy from sunlight : New technology should make solar cells significantly more efficient

US researchers have found a way to significantly increase the performance of solar cells. A photon (light particle) sets two electrons in motion, creating an electric current; so far it is only one electron per photon. A group led by Markus Einzinger and Marc Baldo from the Massachusetts Institute of Technology (MIT) presented their research results in the journal "Nature" (English-language summary: here).

The researchers assume that with the new principle, the currently theoretically conceivable maximum efficiency of solar cells for converting sunlight into electricity can be increased from 29.1 percent to around 35 percent.

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The process: Blue and green light rays have a shorter wavelength than others, but the individual photons have more energy. Their energy would be sufficient to detach two electrons in silicon from their atoms.

As early as 1979, the US physicist David Dexter recognized that this technology is generally possible. If the hydrocarbon tetracene is applied as the top layer on solar cells, two excitons can be obtained from one high-energy photon instead of just one. Excitons are bundles of energy that can move through material like electrons. The difficulty was to transfer these two excitons from the tetracene to the silicon in such a way that two electrons are also set in motion there. Because power losses occur again and again on the silicon surface.

Solution to the problem

A 0.8 nanometer thick intermediate layer of hafnium oxynitride largely prevents these losses. According to Baldo, this layer is crucial: "That is the reason why other researchers were unable to get this process to work," he is quoted in a press release from MIT.

"It's exciting, interesting work, but whether it is relevant for the production of solar cells remains to be seen in the future," says Jan Christoph Goldschmidt from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg. The new development is still a long way from being ready for series production. Currently, the efficiency of the solar cell manufactured by the researchers is only 5.1 percent despite the excitation of two electrons.

In general, it does not always seem to be enough just to further develop technology. In a study in the journal “Nature Energy”, Bart Sweerts from ETH Zurich and his colleagues show that China could generate more solar power if air pollution were less. Sweerts and his team analyzed sunlight data from 119 measuring stations across China. According to their analysis, the potential for solar power generation in China decreased by 13 percent from 1960 to 2015 due to air pollution. (dpa)

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