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Engineering a Practical Full-Spectrum Solar Cell

A solar cell's ability to convert sunlight to electric current is limited by the bandgaps of the semiconductors from which it is made. For example, semiconductors with wide bandgaps respond to shorter wavelengths with higher energies (lower left). A semiconductor with an intermediate band has multiple bandgaps that cover the light spectrum and can respond to a range of energies (lower right). The device was able to absorb energies between 1.1 electron volts (eV) in the infrared range to 3.2 eV at the ultraviolet end of the spectrum.

Researchers led by the Materials Science Division's Wladek Walukiewicz have designed a multiband solar cell in which two distinct materials are alloyed together using a common semiconductor fabrication technique. By engineering an alloy with multiple band gaps—the energies of light that can be absorbed by a material—costly fabrication steps can be avoided. In addition, such a design also improves the power conversion efficiency of solar cells, as a larger portion of the sun's energy can be translated into electrical current.

The team created a test cell by alloying gallium arsenide, a semiconductor employed in solar cells, with gallium nitride, a wide bandgap semiconductor used in light-emitting diodes. Narrow intermediate bands generated within the wide bandgap semiconductor serve as a ladder to promote electrons without conducting charge and thereby shorting out the solar cell.
These findings reveal light from the near-infrared well into the ultraviolet region of the solar spectrum could be absorbed by the multiband junction and converted into current. These results are the first to show a transition between intermediate and conduction energy bands in these materials, unveiling a missing link in the quest for a fully operational multiband solar cell device.


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N. López, L. A. Reichertz, K. M. Yu, K. Campman, and W. Walukiewicz, "Engineering the Electronic Band Structure for Multiband Solar Cells," Physical Review Letters 106, 028701 (2011).