New Understanding of Sodium Application in Solar Cells Offers Promise of Greater Efficiency

Researchers at the University of Luxembourg are discovering that some of the assumptions that have been made about solar cell manufacturing the last 20 years aren’t exactly correct. The discovery offers opportunities to enhance the efficiency of solar cells by designing them with the new understanding built in.

The crux of the issue has to do with the application of sodium.

Based on old assumptions, sodium was added after the growth process of the solar cells was completed. Now, researchers are coming to understand that inserting single grains of sodium strategically can maximize the effect sodium has in making solar cells more efficient.

From phys.org

Researchers refute 20-year-old assumptions in solar cell production

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.

The role of sodium in the manufacturing process

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 homogenise 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 at the University of Luxembourg and an Attract fellow of the Luxembourg National Research Fund (FNR).

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