Sunlight Absorber

A nanoscale pattern could lead to more efficient solar cells

Source: “Broadband 
Polarization-Independent Resonant Light Absorption Using Ultrathin Plasmonic Superabsorbers”
Harry Atwater et al.
Communications 2: 517

Results: Thin films of silver ordinarily absorb only 5 percent of visible light. By applying a pattern of nanoscale shapes to such a surface, researchers increased absorption to 70 percent. The patterned film absorbs light from the entire visible spectrum and from almost any angle.

Why it matters: The advance could lead to solar cells that are far thinner and cheaper than conventional ones, because less semiconductor material would be needed to absorb sunlight. Researchers have known that nanoscale patterns can greatly enhance light absorption by gathering light waves the way antennas gather radio waves. But these patterns typically absorb only light of certain wavelengths, allowing most of the solar spectrum to escape. That makes them impractical for use in solar cells. The researchers have demonstrated that their patterns can be used to absorb a wide range of wavelengths, opening the door for their use in photovoltaic devices.

Methods: The researchers used lithography to carve patterns of tiny wedge shapes placed end to end. The narrow end of the wedges can absorb short wavelengths at the blue end of the spectrum, and the wider end absorbs longer-wavelength red light.

Next Steps: The researchers are working to apply the nanoscale design to materials used in solar cells. In recent, unpublished experiments, they showed that the patterns can allow thin films of silicon to absorb as much light as unpatterned silicon films 25 times as thick.

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