Berkeley researchers Kin Man Yu and Wladek Walukiewicz
(Photo: Berkeley Lab)
Scientists from the U.S. Department of Energy’s Lawrence
Berkeley National Laboratory have come a step closer to the
development of a commercially-viable full-spectrum solar cell.
Traditionally, due to their limited band gap (energy range),
semiconductors used in solar cells have only been able to
respond to a certain segment of the solar spectrum – this
segment varies, according to the semiconductor. Some cells have
been created that respond to everything from low-energy infrared
through visible light to high-energy ultraviolet, but these have
been costly to produce and thus unfit for common use. The new
cell, however, responds to almost the entire spectrum, and can
be made using one of the semiconductor industry’s most common
manufacturing processes.
Given that no one semiconductor alloy can respond to all
wavelengths, the approach used in the past has been to stack
layers of different semiconductors – each one with a different
band gap – and wire them in series. Nine years ago, by
adjusting the amounts of indium and gallium in the alloy indium
gallium nitride, Berkeley’s Wladek Walukiewicz and Kin Man Yu
were able to tweak its band gap to respond to different
wavelengths. Using this technology, they were able to create a
full-spectrum solar cell by stacking different versions of the
same alloy, but the production process was quite complex.
In 2004 they took a different approach, creating a single
alloy of highly mismatched semiconductors based on a common
alloy, zinc (plus manganese) and tellurium. They were able to
add a third band gap, between those of the zinc and tellurium,
by doping the alloy with oxygen. This once again resulted in a
full-spectrum solar cell, but the method of creating it was once
again too complicated and expensive.
Their latest creation is another multiband semiconductor
alloy, gallium arsenide nitride, which has a composition similar
to that of the commonly-used gallium arsenide. In this case, the
third band is created by replacing some of the arsenic atoms
with nitrogen. Unlike their previous efforts, this solar cell
material can be produced via one of the most common methods of
fabricating compound semiconductors – metalorganic chemical
vapor deposition.
When exposed to sunlight, a test cell made with the new
semiconductor was shown to respond strongly to all parts of the
spectrum, making this a significant step in towards more
efficient solar cells that can be mass produced by conventional
methods.
The research was recently published in the journal
Physical Review Letters.
Via
Berkeley Lab.
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