NREL Claims Close To 50% Efficiency For 6 Junction Solar Cell

• NREL has come out with a research in which it claims to have achieved 47.1% efficiency level for a six-junction solar cell
• It used about 140 layers of various III-V materials and each of the junctions was designed to capture light from a specific part of the solar spectrum
• Possible to go beyond 50% efficiency, but the challenge is to reduce the resistive barriers inside the cell that impede the flow of current

The US National Renewable Energy Laboratory (NREL) claims to have fabricated a 47.1% efficiency level for a six-junction solar cell. This is the 'highest' solar conversion efficiency measured under concentrated illumination, it said. At the same time, a variation of the same cell by NREL led to the efficiency 'record' under one-sun illumination at 39.2%.

Till now, the team explains, four-junction III-V concentrator solar cells have demonstrated the highest solar conversion efficiencies. NREL now has gone a step ahead with a six-junction cell.

The team built the solar cell using about 140 layers of various III-V materials and each of the 6 junctions also referred to as photoactive layers, was specially designed to capture light from a specific part of the solar spectrum. These layers, 3 times narrower than a human hair, support the performance of these junctions. Mostly III-V solar cells are used to power satellites and on earth these are used in concentrator photovoltaics.

Concentrating the light helps boosts efficiency of the cell. "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. Single-junction flat-plate terrestrial solar cells have a limit to about 30% solar-to-electricity conversion efficiency but when using multiple junctions and concentrated light, higher efficiencies are possible, as per the researchers.

Researchers believe exceeding 50% efficiency level is very achievable. However, 100% is not possible due to 'fundamental limits' imposed by thermodynamics. Currently, the main impediment to topping 50% efficiency is to reduce the resistive barriers inside the cell that impede the flow of current.

Their research titled Six-junction III-V solar cells with 47.1% conversion efficiency under 143 suns concentration has been published by Nature Energy international journal.