Technological developments
Technological developments
Bismuth-based crystalline material can
boost solar cell efficiency, chip design
Physicists have discovered solar cells,” said Sang-Wook
unusual electronic properties Cheong, physics professor in
in a material that has potential the Rutger University School
to improve solar cell efficiency of Arts and Sciences and one
and computer chip design. of the paper’s five co-authors.
They determined that a crystal “While we still don’t know
made of bismuth, iron and oxy- how efficiently this material
gen can perform an electronic will ultimately perform as a
feat typically not feasible with solar cell, we do need to keep
conventional semiconductors. investigating alternate technol-
It acts as a reversible diode—es- ogies that show potential for
sentially an electronic turnstile improvement.”
that lets current flow in one The crystal that Cheong
direction under certain condi- and his colleagues investigated
tions and in the is a ferroelectric material,
opposite direction under dif- meaning that the crystal ex-
ferent conditions. Traditional hibits electrical polarisation,
semiconductor diodes are not or alignment. This polarisa-
reversible—the direction of tion, which the scientists
current flow that they allow is believe controls the crystal’s
fixed during fabrication. ability to act as a diode, is
They also discovered that known as a ‘bulk effect’—a
diodes made from this material characteristic that permeates
generate current when light the whole crystal.
falls on them, making them a
potential candidate for future
solar cells. The material ap-
pears very sensitive to light at
the blue end of the spectrum, a
property that has the potential
to increase solar cell efficiency.
Diodes made from crystals formed from bismuth, iron and oxygen generate current
“We’ve reached the upper
when light falls on them, making the material a potential candidate for future solar
cells. (Source: Micha L. Rieser)
limit of efficiency with today’s
nanotechnology researchers
purity silicon and other materials normally ends up stuck and never gets out, leading
imrpove performance of
required. Plastic solar cells are made up to inefficient devices. We are working on
plastic solar cells
of layers of different materials, each with the mayonnaise, the mustard, the butter
Researchers at Canada’s National Institute
a specific function, called a sandwich and other ‘special sauces’ that bring the
for Nanotechnology (NINT) and the
structure. Jillian Buriak, a professor of sandwich together and make each of the
University of Alberta have engineered
chemistry at the U of A, NINT principal layers work together. That makes a better
an approach that is leading to improved
investigator and member of the research sandwich, and makes a better solar cell, in
performance of plastic solar cells (hybrid
team, uses a simple analogy to describe the our case.”
organic solar cells).
approach: “Consider a clubhouse sand- After two years of research, these U
The development of inexpensive,
wich, with many different layers. One layer of A and NINT scientists have, by only
mass-produced plastic solar panels is a goal
absorbs the light, another helps to generate working on one part of the sandwich, seen
of intense interest for many of the world’s
the electricity, and others help to draw the improvements of about 30 percent in the
scientists and engineers because of the
electricity out of the device. Normally, the efficiency of the working model.
high cost and shortage of the ultra-high
layers don’t stick well, and so the electricity The team estimates it will be five to sev-
22 – Global Solar Technology – March/April 2009 www.globalsolartechnology.com
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