Six junction solar cell reaches 47 per cent efficiency

April 14, 2020 // By Nick Flaherty
NREL researchers Ryan France (left) and John Geisz fabricated a solar cell that is nearly 50% efficient. Photo by Dennis Schroeder, NREL
A six junction III-V solar cell reaches 47 per cent efficiency for space and solar concentrator applications

Scientists at the National Renewable Energy Laboratory (NREL) in the US have built a solar cell with a record efficiency approaching 50 per cent.

The six-junction solar cell now holds the world record for the highest solar conversion efficiency at 47.1 per cent, which was measured under concentrated illumination. A variation of the same cell also set the efficiency record under one-sun illumination (or normal conditions) at 39.2 per cent.

“This device really demonstrates the extraordinary potential of multijunction solar cells,” said John Geisz, a principal scientist in the High-Efficiency Crystalline Photovoltaics Group at NREL and lead author of a new paper on the record-setting cell.

The paper, “Six-junction III-V solar cells with 47.1% conversion efficiency under 143 suns concentration,” appears in the journal Nature Energy. 

To construct the device, NREL researchers relied on III-V materials. Each of the cell’s six junctions (the photoactive layers) is specially designed to capture light from a specific part of the solar spectrum. The device contains about 140 total layers of various III-V materials to support the performance of these junctions. The high cost means these III-V solar cells are most often used to power satellites where concentrated sunlight is more available.

Each junction contains a window layer, n-type emitter, unintentionally doped (UID) layer, ptype base, and back-surface field (BSF). Each junction layer is a few microns thick, using mixtures of gallium, indium,phosporus, selenium and GaAs.  

On Earth the six-junction solar cell is well-suited for use in concentrator photovoltaics, said Ryan France, co-author and a scientist in the III-V Multijunctions Group at NREL.

“One way to reduce cost is to reduce the required area,” he said, “and you can do that by using a mirror to capture the light and focus the light down to a point. Then you can get away with a hundredth or even a thousandth of the material, compared to a flat-plate

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