background image
scientist at the CEI.
¡°We are hopeful that surface passivation strategies
like this will help improve the performance and stabil-
ity of perovskite solar cells.¡±
Ginger¡¯s and Hillhouse¡¯s teams worked together to
demonstrate that surface passivation of perovskites
sharply boosted performance to levels that would
make this material among the best for thin-film solar
cells.
They experimented with a variety of chemicals for
surface passivation before finding one, an organic
compound known by its acronym TOPO, that boosted
perovskite performance to levels approaching the best
gallium arsenide semiconductors.
¡°Our team at the UW was one of the first to iden-
tify performance-limiting defects at the surfaces of
perovskite materials, and now we are excited to have
discovered an effective way to chemically engineer
these surfaces with TOPO molecules,¡± said co-lead
author Dane deQuilettes, a postdoctoral researcher
at the Massachusetts Institute of Technology who
conducted this research as a UW chemistry doctoral
student.
¡°At first, we were really surprised to find that the
passivated materials seemed to be just as good as
gallium arsenide, which holds the solar cell efficiency
record.¡±
¡°So to double-check our results, we devised a few different approaches to con-
firm the improvements in perovskite material quality.¡±
DeQuilettes and co-lead author Ian Braly, who conducted this research as
a doctoral student in chemical engineering, showed that TOPO-treating a
perovskite semiconductor significantly impacted both its internal and external
photoluminescence quantum efficiencies - metrics used to determine how good
a semiconducting material is at utilizing an absorbed photon¡¯s energy rather
than losing it as heat. TOPO-treating the perovskite increased the internal pho-
toluminescence quantum efficiencies by tenfold - from 9.4 percent to nearly 92
percent.
¡°Our measurements observing the efficiency with which passivated hybrid
perovskites absorb and emit light show that there are no inherent material
flaws preventing further solar cell improvements,¡± said Braly. ¡°Further, by fitting
the emission spectra to a theoretical model, we showed that these materials
could generate voltages 97 percent of the theoretical maximum, (cont. pg3>>)
Thin Solar Cell Efficiency Record: 97% of Theoretical Max
¡°We think we have provided a path forward to better harness the sun¡¯s energy.¡±
more sunshine for
cannabis... Pg 6
cleaner kitchens
are safer... Pg 9
prepare for the
hunt early... Pg 11
pure prairie league
appearance... Pg 12
And then there was (more) light:
Researchers boost performance quality
of perovskites
James Urton, UW News, July 25, 2018: Solar cells are
devices that absorb photons from sunlight and convert
their energy to move electrons - enabling the produc-
tion of clean energy and providing a dependable route
to help combat climate change.
But most solar cells used widely today are thick, fragile
and stiff, which limits their application to flat surfaces
and increases the cost to make the solar cell.
¡°Thin-film solar cells¡± could be 1/100th the thickness of
a piece of paper and flexible enough to festoon surfac-
es ranging from an aerodynamically sleek car to cloth-
ing. To make thin-film solar cells, scientists are moving
beyond the ¡°classic¡± semiconductor compounds, such
as gallium arsenide or silicon, and working instead
with other light - harvesting compounds that have the
potential to be cheaper and easier to mass produce.
The compounds could be widely adopted if they could
perform as well as today¡¯s technology.
In a paper published online this spring in the journal
Nature Photonics (www.nature.com/articles/
s41566-018-0154-z), scientists at the University of
Washington report that a prototype semiconductor
thin-film has performed even better than today¡¯s best
solar cell materials at emitting light.
2018 AUG/SEP #9-4
¡°It may sound odd since solar cells absorb light and turn it into electric-
ity, but the best solar cell materials are also great at emitting light,¡± said
co-author and UW chemical engineering professor Hugh Hillhouse, who
is also a faculty member with both the UW¡¯s Clean Energy Institute and
Molecular Engineering & Sciences Institute.
¡°In fact, typically the more efficiently they emit light, the more voltage
they generate.¡±
The UW team achieved a record performance in this material, known
as a lead-halide perovskite, by chemically treating it through a process
known as ¡°surface passivation,¡± which treats imperfections and reduces
the likelihood that the absorbed photons will end up wasted rather than
converted to useful energy.
¡°One large problem with perovskite solar cells is that too much ab-
sorbed sunlight was ending up as wasted heat, not useful electricity,¡±
said co-author David Ginger, a UW professor of chemistry and chief
(An image of a back-reflector sur-
face used by the researchers to test
perovskite performance. Each quadrant
is a different surface material - gold,
titanium, palladium or a silica compound
- upon which the perovskite material
would be deposited for experiments.
source: www.washington.edu)