ScienceDaily (Apr. 19, 2012) —
Harnessing the energy of sunlight can be as simple as tuning the optical
and electronic properties of metal oxides at the atomic level by making
an artificial crystal or super-lattice 'sandwich,' says a Binghamton
University researcher in a new study published in the journal Physical Review B.
"Metal oxides are cheap, abundant and 'green,'" said Louis Piper,
assistant professor of physics at Binghamton University. "And as the
study proved, quite versatile. With the right touch, metal oxides can be
tailored to meet all sorts of needs, which is good news for
technological applications, specifically in energy generation and flat
Here's how it works: semiconductors are an important class of
materials in between metals and insulators. They are defined by the size
of their band gap, which represents the energy required to excite an
electron from the occupied shell to an unoccupied shell where it can
conduct electricity. Visible light covers a range of 1 (infrared) to 3
(ultraviolet) electron volts. For transparent conductors, a large band
gap is required, whereas for artificial photosynthesis, a band gap
corresponding to green light is needed. Metal oxides provide a means of
tailoring the band gap.
But whilst metal oxides are very good at electron conduction, they
are very poor "hole" conductors. Holes refer to absence of electrons,
and can conduct positive charge. To maximize their technologically
potential, especially for artificial photosynthesis and invisible
electronics, hole conducting metal oxides are required.
Knowing this, Piper has begun studying layered metal oxides systems,
which can be combined to selectively 'dope' (replace a small number of
one type of atom in the material), or 'tune' (control the size of the
band gap). Recent work revealed that a super-lattice of two
hole-conducting copper oxides could cover the entire solar spectrum. The
goal is to improve the performance whilst using environmentally benign
and cheap metal alternatives.
For instance, indium oxide is one of the most widely used oxides used
in the production of coatings for flat screen displays and solar cells.
It can conduct electrons really well and is transparent. But it is also
rare and very expensive. Piper's current research is aimed towards
using much cheaper tin oxide layers to get electron and hole conduction
with optical transparency.
But according to Piper, his research shows that one glove will not fit all purposes.
"It's going to be a case of some serious detective work," said Piper.
"We're working in a world where physics and chemistry overlap. And
we've reached the theoretical limit of our calculations and fundamental
processes. Now we need to audit those calculations and see where we're
missing things. I believe we will find those missing pieces by playing
around with metal oxides."
By reinforcing metal oxides' 'good bits' and downplaying the rough
spots, Piper is convinced that the development of new and exciting types
of metal oxides that can be tailored for specific applications are well
within our reach.
"We're talking battery storage, fuel cells, touch screen technology
and all types of computer switches," said Piper "We're in the middle of a
very important gold rush and its very exciting to be part of that race
to strike it rich. But first we have to figure out what we don't know
before we can figure out what we do. One thing's for sure: metal oxides
hold the key. And I believe that we at Binghamton University can
contribute to these efforts by doing good science and taking a morally
The above story is reprinted from materials provided by Binghamton University, State University of New York, via Newswise.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
- S. Sallis, L. Piper, J. Francis, J. Tate, H. Hiramatsu, T. Kamiya, H. Hosono. Role of lone pair electrons in determining the optoelectronic properties of BiCuOSe. Physical Review B, 2012; 85 (8) DOI: 10.1103/PhysRevB.85.085207