Tech Briefs Magazine - April 2024 - 22

Combination of Stressors Key to Testing Perovskite
Solar Cells
High temperature and illumination is the most critical combination of stressors for understanding
how well a perovskite solar cell will perform outdoors.
National Renewable Energy Laboratory, Golden, CO
P
erovskite solar cells should be subjected
to a combination of stress
tests simultaneously to best predict how
they will function outdoors, according
to researchers at the U.S. Department
of Energy's National Renewable Energy
Laboratory (NREL).
Solar cells must endure a set of harsh
conditions - often with variable combinations
of changing stress factors - to judge
their stability, but most researchers conduct
these tests indoors with a few fixed
stressing conditions. While these tests provide
some necessary insight, understanding
which stressor applied during indoor
tests provided predictive correlations with
outdoor operation is critical.
" We must understand how well perovskite
solar cells will perform outdoors,
under real conditions, to move
this technology closer to commercialization, "
said Kai Zhu, a Senior Scientist
in the Chemistry and Nanoscience
Center at NREL. " That's why we identified
accelerated testing protocols that
can be conducted in the laboratory to
reveal how these cells would function
after six months in operation outside. "
Zhu is lead author of a newly published
paper, " Towards linking lab and
field lifetimes of perovskite solar cells, "
which appears in the journal Nature.
His co-authors from NREL are Qi Jiang,
Robert Tirawat, Ross Kerner, E. Ashley
Gaulding, Jimmy Newkirk, and Joseph
Berry. Other co-authors are from the
University of Toledo, who have collaborated
with Zhu on several other recent
papers about perovskites.
Outdoor conditions, such as humidity,
heat, and even light, put stress on
solar cells. As a result, the efficiency of
solar cells declines and power production
decreases over time. To reach the
reliability targets for commercialization
of perovskite technology, protocols
must first be established so that improvements
from different groups can
be easily validated and compared.
Researchers tend to test the stability
of perovskite solar cells by exposing
them to light and under low temperatures.
However, a broad range of testing
conditions exist, making it challenging
to compare different studies and discern
their relevance to achieving the reliability
needed for commercialization.
The team put perovskite solar cells
through a battery of tests. During the
test for operational stability, the cells
retained more than 93 percent of their
maximum efficiency after about 5,030
hours of continuous operation. The cells
were subjected to thermal cycling, with
temperatures repeatedly fluctuating between
-40 °C and 85 °C. After 1,000 cycles,
the cells showed an average of about
5 percent degradation.
The tests addressed different stressors,
such as light and heat, separately.
However, in real-world conditions,
these individual factors act simultaneously
to affect solar cell performance.
When combined, for example, light
and heat significantly accelerate performance
degradation or cause new
problems that were otherwise absent
or occurring at slower rates when testing
separately.
The researchers concluded that
high temperature and illumination
is the most critical combination of
stressors for understanding how well a
perovskite solar cell will perform outdoors.
The U.S. Department of Energy
Solar Energy Technologies Office
funded the research.
For more information, contact David
Glickson at david.glickson@nrel.gov;
303-275-4097.
Conductive Carbon Fiber Polymer Composite
The light weight and strength of carbon fiber composite with the thermal conductivity of
metal alloys.
Langley Research Center, Hampton, VA
A
22
team of inventors from NASA Langley
and NASA Ames have created a
new type of carbon fiber polymer composite
that has a high thermal conductivity.
This was achieved by incorporating
Pyrolytic Graphite Sheets (PGSs) and
Carbon Nanotubes (CNTs), which enhance
the material's ability to transfer
heat when compared to typical carbon
fiber composites.
Carbon fiber polymer composites
are frequently used in aerospace structures
because they are light, strong,
and require minimal maintenance.
However, they typically have poor thermal
conductivity, which limits their use
to applications where heat transfer is
not required. Where heat transfer is
needed, aluminum alloys are used instead,
but they have drawbacks such as
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lower strength, higher weight, and increased
maintenance needs compared
to composites. The new material developed
by NASA addresses this issue by
combining the benefits of a carbon fiber
composite with the high thermal
conductivity of metal alloys.
NASA has also improved the composite
manufacturing process to ensure better
thermal conductivity not only on the
Tech Briefs, April 2024

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Tech Briefs Magazine - April 2024

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