Read out The best solar cells made of crystalline silicon today deliver electricity with an efficiency of around 30 percent. German and Australian physicists have now found a way to increase this yield by a third. For this purpose, the energy of only one light particle to be distributed to two photons. So far, a part of the energy of certain light particles is lost in the form of heat, this excess energy could now also be used with a photon divider for electricity production, the researchers report in the journal "Journal of Applied Physics" (Vol 92, p 1668). "A maximum conversion efficiency of 39.63 percent can be achieved, " write Peter Würfel from the University of Karlsruhe and his Australian colleagues from the University of South Wales.

Solar cells generate electricity by "shoving" electrons from the incident sunlight out of their normal orbit into the so-called conduction band. To overcome this band gap, the photons must transmit a fixed amount of energy to the electrons. However, some light particles carry at least twice as much energy as is actually necessary for this electron jump. If this energy is previously lost in the form of heat, an upstream photon splitter can transfer this energy to two light particles. Both photons could then excite electrons and produce electricity over them.

To turn their idea into a prototype, scientists propose an additional layer of aluminum arsenide or gallium phosphide. Applied to the solar cell, this material captures the high-energy photons. In this case, electrons are put into an excited state for a short time. If they fall back to their original energy level over two levels, two photons are to be created. Both then carry enough energy to generate electricity in the silicon crystal.

The best yield is theoretically possible if this photon splitter is located on the backside of the solar cell. A disadvantage here is that most semiconductor cells, such high-energy light particles can not fly through unhindered. Certain "dye-sensitized cells" offer themselves here as a solution. But even if the photon splitter is located on the front, the current efficiency could be increased to a maximum of 38.6 percent. display

Jan Oliver Löfken


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