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A new record in solar cells

University of Delaware beats old record. Solar cells now hit 42.8 percent efficiency.

The University of Delaware has inched up the record for solar cell efficiency with a new device that can convert 42.8 percent of the light that strikes it into electricity.

That beats the old record of 40.7 percent hit in December. The Defense Advanced Research Projects Agency, or DARPA, has been funding research to get efficiency up to 50 percent.

The cell, created by Christina Honsberg and Allan Barnett of UD, splits incoming light into three buckets: high energy, low energy, and medium energy light. The light is then directed to different materials, which then extract electrons out of the photons that make up sunlight.

The device also has an optical concentrator, sort of like a lens that directs more sunlight to the solar cell than would occur naturally and thereby increasing efficiency.

Various materials (silicon, germanium, etc.) react differently to different parts of the solar spectrum. Crystalline solar cells, for instance, can currently convert 22 percent of light into electricity (without concentrators). The theoretical maximum is sans concentration. Combining different materials into multi-junction cells or adding concentrators helps get around the limitations of the materials.

Multi-junction solar cells and concentrators, however, are expensive. The initial customers for devices like this will be the military. Possible applications include portable charging packs for soldiers.

Concentrators can often add girth to solar cells, but the UD device is a little less than a centimeter thick.