Wednesday, 31 July 2013

Researchers overcome technical hurdles in quest for inexpensive, durable electronics and solar cells

Researchers overcome technical
hurdles in quest for inexpensive,
durable electronics and solar cells

Light is emitted from excited argon
gas atoms flowing through the glass
tube of a plasma reactor. The plasma
is a reactive environment used to
produce silicon nanocrystals that can
be applied to inexpensive, next-
generation electronics. Credit:
University of Minnesota
Electronic touch pads that cost just a
few dollars and solar cells that cost
the same as roof shingles are one
step closer to reality today.
Researchers in the University of
Minnesota's College of Science and
Engineering and the National
Renewable Energy Laboratory in
Golden, Colo., have overcome
technical hurdles in the quest for
inexpensive, durable electronics and
solar cells made with non-toxic
chemicals. The research was
published in the most recent issue of
Nature Communications , an
international online research journal.
"Imagine a world where every child
in a developing country could learn
reading and math from a touch pad
that costs less than $10 or home
solar cells that finally cost less than
fossil fuels," said Uwe Kortshagen, a
University of Minnesota mechanical
engineering professor and one of the
co-authors of the paper.
The research team discovered a novel
technology to produce a specialized
type of ink from non-toxic
nanometer-sized crystals of silicon,
often called " electronic ink." This
"electronic ink" could produce
inexpensive electronic devices with
techniques that essentially print it
onto inexpensive sheets of plastic.
"This process for producing
electronics is almost like screen
printing a number on a softball
jersey," said Lance Wheeler, a
University of Minnesota mechanical
engineering Ph.D. student and lead
author of the research.
But it's not quite that easy. Wheeler,
Kortshagen and the rest of the
research team developed a method
to solve fundamental problems of
silicon electronic inks.
First, there is the ubiquitous need of
organic "soap-like" molecules, called
ligands , that are needed to produce
inks with a good shelf life, but these
molecules cause detrimental residues
in the films after printing. This leads
to films with electrical properties too
poor for electronic devices. Second,
nanoparticles are often deliberately
implanted with impurities, a process
called "doping," to enhance their
electrical properties.
In this new paper, researchers
explain a new method to use an
ionized gas, called nonthermal
plasma, to not only produce silicon
nanocrystals, but also to cover their
surfaces with a layer of chlorine
atoms. This surface layer of chlorine
induces an interaction with many
widely used solvents that allows
production of stable silicon inks with
excellent shelf life without the need
for organic ligand molecules. In
addition, the researchers discovered
that these solvents lead to doping of
films printed from their silicon inks,
which gave them an electrical
conductivity 1,000 times larger than
un-doped silicon nanoparticle films.
The researchers have a provisional
patent on their findings.
"What this research means is that we
are one step closer to producing
more pure and more stable electronic
ink with non- toxic chemicals ,"
Kortshagen said. "The bigger goal
here is to find a way that this
research can benefit everyone and
make a real difference."
More information: "Hypervalent
Surface Interactions for Colloidal
Stability and Doping of Silicon
Nanocrystals," Nature
Communications , http://
www.nature.com/
ncomms/2013/130729/ncomms3197/
full/ncomms3197.html
Provided by University of Minnesota

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