Perovskite tandem solar cells achieve over 29% efficiency with simple salt tweak

Researchers in Lithuania have increased tandem perovskite solar cell efficiency to more than 29 percent after modifying an ultra-thin molecular layer that transfers positive charge carriers within the device. Kaunas University of Technology (KTU) scientists and their international partners created a more stable interface between different layers of the solar cells. This reduced the corrosion and made it possible for the cells to maintain higher efficiency and performance. Kasparas Rakštys, PhD, a researcher at KTU, pointed out that these layers must be perfectly interconnected for the device to operate efficiently. “Simply put, a solar cell can be imagined as a multi-layered sandwich in which each layer is made of a different material and performs a specific function,” he added. The solution involved altering the molecular group responsible for bonding with the metal oxide layer. Instead of its conventional acidic form, they turned it into an ionic salt. With this new method, perovskite tandem solar cells achieved a power conversion efficiency of more than 29 percent. Protecting the interface Perovskite solar cells are thin-film photovoltaic (PV) devices that use a perovskite material as the active layer. They’re considered a promising energy technology as they’re lightweight, flexible, and relatively cheap to manufacture. However, their performance can deteriorate when exposed to moisture, oxygen, and heat. A solar cell consists of several layers that must work together to collect and transport electrical charges. Problems at the interfaces between these layers can significantly affect the performance of the cell. Until recently, scientists relied on charge-transporting self-assembled monolayers (SAMs). Initially introduced in 2018, these are thin layers of molecules that act like molecular glue. They transport positive charge carriers, known as holes, toward an electrode. Nonetheless, Rakštys noted that a particular problem emerged over time. “Due to their acidic nature, these molecules can gradually corrode adjacent layers, creating defects at the interface that hinder charge transport,” he stressed. “As a result, the solar cell becomes less efficient and its operational lifetime is reduced.” That’s why the researchers decided to modify the part of the SAM molecule that attaches to the metal oxide contact layer. As reported, they chemically converted the molecules into neutral ionic salts. A molecular quick fix “In this study, we simply neutralized the acidic molecules by converting them into chemically neutral salts, creating a non-aggressive interface that allows the solar cell to operate much more stably and efficiently,” Rakštys stated, adding that the approach offers several technological benefits. The resulting salt molecules bind just as strongly to metal oxide surfaces. They are additionally water-soluble, which means that the layer can be deposited without relying on toxic solvents. Despite being only a few nanometers thick, the modified layer can have a great effect on how efficiently charges travel through the device. To test whether the solution could be applied in practice, the researchers worked together with partners in China. They showed that it does work on large-area modules. It produced a uniform, high-quality coating that’s suitable for more practical testing The method was also tested in perovskite tandem solar cells, which use different light-absorbing layers to capture a broader portion of the solar spectrum. “Using our new approach, we achieved a power conversion efficiency greater than 29 percent in perovskite tandem solar cells – one of the highest values reported to date,” Rakštys concluded. He and his team now believe that the technology could eventually lead to more versatile solar devices, like cells added to building facades, windows, and textiles. They have already applied for a patent and are moving toward commercial use.The study has been published in the journal Nature Communications.Get the latest in engineering, tech, space & science - delivered daily to your inbox.Based in Skopje, North Macedonia. Her work has appeared in Daily Mail, Mirror, Daily Star, Yahoo, NationalWorld, Newsweek, Press Gazette and others. She covers stories on batteries, wind energy, sustainable shipping and new discoveries. When she's not chasing the next big science story, she's traveling, exploring new cultures, or enjoying good food with even better wine.