Tech Briefs Magazine - August 2021 - 40

Power & Energy
i.e., the sharing of electron pairs between
aluminum and carbon atoms. While electrodes
in conventional rechargeable batteries
are only two-dimensional, this technique
uses a three-dimensional - or nonplanar
- architecture and creates a deeper,
more consistent layering of aluminum
that can be finely controlled.
2 μm
This magnified image shows aluminum deposited on carbon fibers in a battery electrode. The
chemical bond makes the electrode thicker and its kinetics faster, resulting in a rechargeable battery
that is safer, less expensive, and more sustainable than lithium-ion batteries.
Flexible Organic Photovoltaics
These organic solar cells can be useful where constant, low power generation is sufficient.
Rice University, Houston, Texas
O
rganic solar cells rely on carbonbased
materials including polymers
- as opposed to hard, inorganic materials
like silicon - to capture sunlight and
translate it into current. Organics are
also thin, lightweight, semi-transparent,
and inexpensive. While commercial silicon-based
solar cells perform at about
22 percent efficiency, organics top out at
around 15 percent.
One approach to fixing the problem is
to find polymers or other organic semiconductors
that are flexible by nature. A
new approach incorporates a network of
elastic additives that make the electrically
active material less brittle with little to no
loss of current flow. Rather than make a
mesh and pour in the semiconducting
polymers, sulfur-based thiol-ene reagents
were mixed in. The molecules blend with
the polymers and then crosslink with
each other to provide flexibility. Too little
thiol-ene leaves the crystalline polymers
prone to cracking under stress, while too
much dampens the material's efficiency.
The researchers replaced 20 percent of
the active layer with the mesh. Cells
retained their efficiency and gained flexibility.
The next step was to stretch the
material. Pure P3HT (the active polythiophene-based
layer) started cracking at
about 6 percent strain. When 10 percent
thiol-ene was added, the percentage in -
creased to 14. At around 16 percent
strain, cracks were observed throughout
the material.
At strains higher than 30 percent, the
material flexed well but became useless as
a solar cell. Essentially, there was no loss in
photocurrent up to about 20 percent.
Damage under strain affected the material
even when the strain was released.
The researchers are testing different
organic photovoltaic materials while
working to make them more stretchable
with less additive for larger test cells.
For more information, contact Mike
Flexible organic photovoltaics feature a chemical additive that mitigates the material's brittle qualities
without losing efficiency. (Photo by Jeff Fitlow)
40
Cov
www.techbriefs.com
ToC
Williams at mikewilliams@rice.edu; 713348-6728.
Tech
Briefs, August 2021
The aluminum-anode batteries can be
reversibly charged and discharged one
or more orders of magnitude more
times than other aluminum rechargeable
batteries under practical conditions.
The substrates provide a large ther -
modynamic driving force that promotes
nucleation. Runaway - unsafe growth
of the metal electrode - is prevented by
forces such as surface tension that can
be massive at small scales.
For more information, contact Jeff Tyson
at jeff.tyson@cornell.edu; 607-793-5769.

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Tech Briefs Magazine - August 2021

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