Corrosion-preventing technique improves perovskite solar cells

Long sought after for its superconducting, electronic, and ferroelectric properties as well as applications in areas such as nanotechnology, perovskite has become one of the most attractive materials for the next generation of solar cells. But while perovskite solar cells are poised to take over that top position among photovoltaic technologies—because they’re inexpensive to manufacture, lightweight, flexible, and thin—challenges do still exist. Now, researchers are working to overcome them.

Perovskite materials in such solar cells can degrade quickly under various environmental conditions, including high temperatures and even UV light. Essentially, they’re currently unstable. Researchers at Kaunas University of Technology (KTU; Lithuania), in conjunction with scientists from Lausanne Federal Institute of Technology (EPFL; Switzerland) and other research organizations around the world, have discovered that passivation (a metal finishing process that prevents corrosion) of an active solar cell layer can boost the cell’s efficiency and significantly improve its stability.

Current techniques involve post-treatment of the surface by alkylammonium halides; this does achieve better efficiency and stability of perovskite solar cells and devices, but it requires an additional 2D perovskite layer on top of the primary perovskite absorber layer post-treatment. The 2D layer acts as a shield from high temperatures, humidity, etc.

“Passivation has been applied previously, but so far, a two-dimensional layer of perovskite is being formed on the traditional three-dimensional perovskite light absorber, making it difficult for carriers to move, especially at higher temperatures,” says study co-author Dr. Kasparas Rakštys, a professor and lead researcher at KTU. “This is a very appealing area because perovskite solar cells are currently one of the fastest-growing technologies, and their successful commercialization could contribute to climate change solutions.”

In the study, published in Nature Communications, passivation was shown to eliminate both shallow- and deep-level defects in perovskite material that can occur during the manufacturing process. Specifically, passivation causes a perovskite surface to become chemically inactive, making it more resistant to environmental conditions surrounding them. According to the researchers, the perovskite solar cells “ultimately achieve[d] an efficiency of 23.9% with long-term operational stability (over 1000 h).”

The 3D perovskite layer’s surface was “passivated by different isomers of phenylethylammonium iodide” as part of the study. The researchers note that “these isomers have the same molecular formula but different arrangements of atoms in space, determining the probability of 2D perovskite formation.” The EPFL team, in testing the perovskite materials via mini modules, demonstrated a 21.4% solar energy conversion efficiency with the perovskite solar cells.

“It has been discovered that an isomer with the passivation groups closest to each other lead to the most efficient passivation due to the steric hindrance that avoids 2D perovskite formation,” Rakštys says.

In previous work with solar cell technology, KTU researchers, alongside physicists from Helmholtz-Zentrum (Berlin), were able to improve the efficiency of tandem silicon-perovskite solar cells to 29.8%. And now, they are studying functional, hole-transporting materials and new perovskite compositions to further advance perovskite solar cells and other devices.