Solar cells typically convert no more than 20 percent of incoming energy
into electricity, in part because they capture only certain wavelengths
of light. Researchers at Germany’s Fraunhofer Institute for Solar
Energy Systems have developed a solar cell that converts 44.7 percent—a
new record. It consists of a lens that concentrates sunlight onto four
stacked subcells, each designed to absorb a distinct portion of the
spectrum. The team estimates it will take them another two to three
years to scale up the 5.2-millimeter prototype for use in solar-power
plants.
1. Sunlight passes through a multifaceted lens known as a Fresnel.
The lens focuses direct sunlight, delivering the power equivalent of 297
suns to the solar cell below.
2. The first subcell, made from
gallium indium phosphide, captures photons from the shortest wavelengths
of light. The subcells beneath it contain elements capable of capturing
progressively longer wavelengths.
3. Each subcell consists of
several semiconductor layers, which create an electric field. As photons
enter, they excite electrons, freeing them from the subcell.
4.
Once the freed electrons reach the top of the stack, a metal contact
funnels them toward an output terminal as a direct current.
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