The physicists published their findings in the renowned scientific journal Nature Communications.
Photovoltaic solar panels convert sunlight into electrical energy. The panels absorb incoming light, which excites electrons that are sent in a predefined direction to generate an electric current that can control motors or power a light bulb. This works through the interaction of several layers of semiconductors and metals within the solar panel. The cells are manufactured in a complex process where various chemical elements are deposited onto a glass substrate, usually by evaporation. In this way, a solar cell "grows," layer by layer.
In the past, scientists accidentally discovered that the efficiency of a certain type of solar cell technology greatly improved when sodium was added to the light-absorbing layer. However, they also observed that sodium affected the growth of this layer and the interaction of the other chemical elements, specifically inhibiting the mixing of gallium and indium. This resulted in less homogeneous layers and, consequently, negatively impacted performance. Therefore, scientists and manufacturers previously believed that the ideal way to produce a solar cell was to add sodium only after the growth process was complete.
Using a different approach, researchers from the Research Unit in Physics and Materials Science at the University of Luxembourg, along with four international partners, have shown that the truth is more nuanced. While conventionally, the light-absorbing layer is composed of thousands of individual grains, the research group chose a more demanding manufacturing strategy and grew the layer as a single grain. "Essentially, in this work we demonstrated that if the absorber is made of a single grain, adding a small amount of sodium helps to homogenize the distribution of the elements," says Diego Colombara, now a Marie Curie researcher at the International Iberian Laboratory of Nanotechnology and principal investigator of the study. "This is very surprising, because for more than 20 years previous research has consistently shown the opposite effect in absorbers made of many grains.".
The researchers concluded that sodium has a dual effect: it homogenizes the elements within each grain but slows down homogenization in the interaction between grains. "This gives us an opportunity to rethink how we produce solar cells. In the future, these insights could lead to improvements in the manufacturing process," concluded Dr. Phillip Dale, head of the research group at the Energy Materials Laboratory (LEM) at the University of Luxembourg and a member of the Luxembourg National Research Fund (FNR).

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