Perovskite solar cells are considered promising, but their service life is limited. Staff at the Korea Institute of Energy Research (KIER) have developed a catalytic process that makes it possible to do without lithium salts - substances that accelerate wear. The results were published in the journal Advanced Science.
Perovskite is a material with the same crystal structure as calcium titanate that absorbs light well. It is often used in the top layer of tandem cells, where several layers are stacked on top of one another to make fuller use of solar energy. Perovskite cells are divided by layer order into conventional and inverted architecture.
In the conventional architecture, lithium salts and additives for better solubility are added to the layer that conducts electric charge (the hole transport layer). This increases conductivity, but at high temperature and humidity the additives evaporate, voids appear between the layers, and lithium ions penetrate uncontrollably into the cell. As a result, the service life is shortened. Until now there were no alternatives giving the same effect without lithium.
The KIER solution: lithium is used only for the necessary chemical reactions and then removed. The key component is nickel oxide powder. It strongly attracts lithium ions and separates them from the salts without additional additives. After the reactions, the powder with lithium is filtered out, and neither lithium nor the catalyst remains in the solution. A defect-free layer is made from it.
Tests showed that at 85 degrees Celsius and 85 percent relative humidity, the cells retained 95 percent of their initial efficiency after 1000 hours. The energy conversion coefficient (efficiency - the share of light converted into electricity) was 25.24 percent versus 25.21 percent for the traditional process with additives. That is, efficiency not only did not fall but turned out to be even slightly higher.
Project leader Sejin An noted that the technology could become an important milestone in solving the service-life problems of tandem perovskite cells and open the way to their commercialization. The work was carried out jointly with the group of Professor Dong Suk Kim of UNIST.
Note: this concerns laboratory samples, not finished panels for sale. For now it is only a step toward more durable solar cells.