Australian scientists set a milestone in solar cell efficiency by claiming a new solar cell array which is 34.5 percent efficient at converting unfocused sunlight into electricity, edging closer to the theoretical limits of sunlight-to-electricity conversion of 53 percent by solar cells.
The new record with a 28 cm2 mini-module embedded in a prism, according to the U.S. National Renewable Energy Laboratory, is a 44 percent improvement over the previous record made by Alta Devices of the USA, which reached 24%, over a larger surface area of 800-cm2.
Mark Keevers and Martin Green of the University of New South Wales (UNSW) say the new solar cell array is far beyond most commercially available silicon photovoltaics, the types found on rooftops and in solar farms, which top out at around 16 to 18 percent efficiency.
The record-setting device combines a silicon cell on one face of a glass prism, with a triple-junction solar cell on the other. The triple-junction cell uses three layers of semiconductor materials to target different wavelengths of sunlight: indium-gallium-phosphide, indium-gallium-arsenide; and germanium. Additional wavelengths are reflected toward a fourth layer made of silicon. This causes the cell to handle much wider range of wavelengths than is possible with a silicon cell alone, leading to increased conversion efficiency.
“The cell shaped like a prism passively gathers light coming from a wide range of angles. The prism also guides the light from the triple-junction cell on one side to the silicon on the other”, Martin said.
Although the device is costlier than conventional solar cells due to the complexity of the design and the cost of the materials, the manufacturing cost may be offset by increased efficiency. Materials such as copper-zinc-tin-sulfide and perovskites well suited for photovoltaics can result in reduced costs, he added.
Further, the researchers say they are aiming for a cell with a conversion efficiency of 40 percent. They’d already achieved that with a cell that used a lens to concentrate sunlight, but this design would not require a lens.
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