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Copper nanowires for new solar cells
By looking at a piece of material in cross-section, a re-
search team led by Parag Banerjee, Washington Univer-
sity, St. Louis, discovered how copper sprouts grasslike
nanowires that could one day be made into solar cells. The
team worked with copper foil, a simple material similar
to household aluminum foil. When most metals are
heated, they form a thick metal oxide film. However, a few
metals, such as copper, iron, and zinc, grow grasslike
structures known as nanowires, which are long, cylindri-
cal structures a few hundred nanometers wide by many
microns tall. Researchers set out to determine how the
nanowires grow.
Raman spectroscopy was used to reveal an underlying
thick filmmade up of two different copper oxides (CuO and
Cu2 O) with narrow, vertical columns of grains running
through them. In between these columns, grain boundaries
acted as arteries through which the copper from the underly-
ing layer was being pushed through when heat was applied,
creating the nanowires. For more information: Parag Banerjee,
314.935.3537, , .
Dual carbon battery is energy dense and sustainable
Power Japan Plus, San Francisco, launched a new battery technology—the Ryden dual
carbon battery that offers energy density comparable to a lithium ion battery, but over a
much longer functional lifetime with drastically improved safety and sustainability. The
new battery makes use of a unique chemistry, with both the anode and cathode made of
carbon. It charges 20 times faster than lithium-ion batteries and is more powerful than
other advanced batteries, operating above four volts. The battery allows for consolidation
of the supply chain by using only one active material. Additionally, manufacturing of the
Ryden battery is under no threat of supply disruption or price spikes from rare metals, such
as rare earths or heavy metals. It is said to be the first high-performance battery that meets
consumer lifecycle demand, rated for more than 3000 charge/discharge cycles. It also elim-
inates the unstable active material used in other high performance batteries, greatly re-
ducing fire and explosion hazards. The Ryden battery can be charged and discharged with
no damage to the battery and is 100% recyclable. .
Better battery design reduces fire risk
As news reports of lithium-ion battery (LIB) fires in Boeing Dreamliner planes and
Tesla electric cars remind us, these batteries—which are in everyday devices like tablets and
smartphones—have their downsides. Scientists designed a safer kind of lithium battery
component that is far less likely to catch fire and still promises effective performance. Lyn-
den Archer, Geoffrey Coates, and colleagues at Cornell University, Ithaca, N.Y., explain
that the danger of LIBs originates with their electrolytes, which usually contain a flamma-
ble liquid. To minimize this fire hazard, more stable, solid electrolytes are being developed.
However, although solid electrolytes are less likely to fuel a fire, their ability to transport
ions has fallen short, especially at room temperature. The Coates team set out to tackle
both issues and develop a safer, high-performance battery component, while Archer’s team
studied the electrochemical characteristics of the materials. Their efforts have led to a new
family of solid polymer electrolytes that is both good at conducting lithium ions at room
temperature and minimizing the risk of fire. Not only are these materials safer than their
liquid counterparts in LIBs, they could also be used in high-energy lithium-metal batter-
ies, such as promising lithium-sulfur and lithium-air batteries. For more information: Lyn-
den Archer, 607.254.8825, , .
ADVANCED MATERIALS & PROCESSES • AUGUST 2014 12
ENERGY TRENDS
briefs
Semprius Inc., Durham, N.C., in
collaboration with researchers at
the University of Illinois at
Urbana-Champaign and Solar
Junction, San Jose, Calif.,
manufactured the first four-
junction, four-terminal stacked
solar cell using its proprietary
printing process. The stacked solar
cell is comprised of a three-
junction microcell stacked on top
of a single-junction germanium
microcell using a high-speed micro
transfer printing method, enabling
simultaneous formation of
thousands of stacked microcells
with very high yields. By using four
junctions, light is captured across
a broader portion of the solar
spectrum and efficiencies much
higher than conventional silicon
and thin-film single-junction solar
cells are achieved. Initial trials
yielded solar cells with efficiencies
up to 43.9%. .
AML Superconductivity and
Magnetics, Palm Bay, Fla., and
Argonne National Laboratory, Ill.,
announced that one of the world’s
most sophisticated super-
conducting magnet systems
passed a landmark reliability test.
The successful test is the latest in
a series of recent AML milestones
that promises to accelerate the
mainstreaming of super-
conductivity into high-impact
applications.
,
A team led by researchers at
Oxford University, UK,
demonstrated that the lead in solar
cells based on lead halide
perovskites can be replaced with
tin. Perovskite solar cells promise
to be inexpensive and easy to
mass produce and have already
achieved 17% efficiency at turning
sunlight into electricity. The
prototype lead-free material
degrades in the presence of
oxygen and moisture, but
researchers are confident that
further work will enable
manufacturing of stable cells that
can operate in air for long periods
of time. .
Schematic illustration of the
cross-section and phases
observed during copper
oxidation. Center photo shows
copper being pushed upward
through the grain boundaries to
become nanowires.