Solar Cell Sets World-Record Conversion Efficiency

Researchers at DOE's National Renewable Energy Laboratory (NREL) have developed a solar cell that can convert a record 40.8 percent of the sunlight that hits it into electricity. The new NREL solar cell is a triple-junction device, which means it uses three layers of photovoltaic material stacked atop one another to catch different parts of the solar spectrum. Sunlight that isn't converted into electricity by the top layer passes into the lower layers of the solar cell, which convert more of the sunlight into electricity, boosting the cell's conversion efficiency.

The cell is unique in that it is grown in an inverted order, from the top down, and is then removed from the substrate it is grown on to produce a lightweight, flexible film. The inverted approach also allows the use of a bottom layer material with a different crystalline lattice spacing than the other materials in the cell, which makes it a "mismatched lattice" or "metamorphic" solar cell. NREL's inverted metamorphic triple-junction solar cell also won an R&D 100 Award this year. It achieved its record efficiency while exposed to sunlight concentrated by a factor of 326 — in industry parlance, "326 suns." 

In recent weeks, researchers around the world have unveiled innovative approaches to capturing sunlight. DOE's Idaho National Laboratory, for instance, has developed a method of producing plastic sheets that contain billions of "nanoantennas" — antennas on the scale of a billionth of a meter — to convert the sun's infrared rays into electricity. The nanoantennas consist of tiny gold squares or spirals set in a specially treated layer of polyethylene, a common plastic.