Assumptions on the production of solar cells that were commonplace for the past 20 years have been proven to be inaccurate by Luxembourg researchers.
Researchers from the University of Luxembourg have investigated the manufacturing process of solar cells and proven that common assumptions on chemical processes are, in fact, inaccurate. The physicists published their findings in the renowned scientific journal Nature Communications.
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 international partners, have now been 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.
Diego Colombara, now Marie Curie Research Fellow at the International Iberian Nanotechnology Laboratory and the principal investigator of the study, stated that: “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. 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).