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Luxembourg Researchers Refute Assumptions In Solar Cell Production

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Research led by the University of Luxembourg investigated the manufacturing
process of solar cells. The researchers proved that assumptions on chemical
processes that were commonplace among researchers and producers for the past 20
years are, in fact, inaccurate. The physicists published their findings in the
renowned scientific journal Nature Communications.


Photovoltaic solar panels convert sunlight into
electrical power. The panels absorb the incoming light which excites electrons
sending them off in a predefined direction in order to generate an electric
current that can drive motors or light a bulb. This works through the
interaction of several layers of semiconductors and metals in the solar panel.
The cells are manufactured in a complex process where several chemical elements
are deposited on a glass substrate, typically by evaporation. Thereby, a solar
cell “grows", layer by layer.


In the past, scientists discovered by accident
that the efficiency of one type of solar cell technology improves vastly if
they add sodium to the light absorbing layer. At the same time, they observed
that the sodium impacts the growth of this layer and the interaction of the other
chemical elements, namely it inhibits the mixing of gallium and indium. This
leads to less homogenous layers and thus impairs the results. Therefore, in the
past, scientists and manufacturers believed that the ideal way to produce a
solar cell was to only add the sodium after the growth process was
concluded.


By using a different approach, researchers from
the Physics and Materials Science Research Unit at the University of
Luxembourg, along with four internationals partners, now were able to show that
the truth is more nuanced. While conventionally the light-absorbing layer is
made up of thousands of individual grains, the research group chose a more
demanding fabrication strategy and grew the layer as a single grain.
“Essentially, in this work we show that if the absorber is made of only one
grain, adding a small amount of sodium helps to homogenize the distribution of
the elements," said Diego Colombara, now Marie Curie Research Fellow at the
International Iberian Nanotechnology Laboratory and the principal investigator
of the study. “This is very surprising, because more than 20 years of previous
research have consistently shown the opposite effect on absorbers made of many
grains."


The conclusion of the researchers is that
sodium has a dual effect: it homogenises the elements inside each grain but it
slows down homogenisation in the interplay between grains. “This gives us the
opportunity to rethink how we produce solar cells. In the future, these
insights might lead to improvements in the manufacturing process," concluded Dr
Phillip Dale, the head of the research group at the Laboratory for Energy
Materials (LEM) at the University of Luxembourg and an Attract fellow of the
Luxembourg National Research Fund (FNR).



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