Perovskite solar cells (PSCs) are one of the world’s fastest-growing solar cell technologies. These elements are thin-layered, lightweight, flexible, and are made of low-cost materials. However, this sort of solar cell still faces a major issue: the very quick degradation of perovskite under thermal conditions.
Passivation is a simple but effective way to improve the stability of perovskite solar cells and has been considered as one of the most effective strategies for eliminating the defects of perovskite materials and their negative effects. The passivated perovskite surface becomes more resistant to external conditions such as temperature or humidity, and more stable, extending the life of the device.
KTU synthesised materials were used in mini-solar modules
KTU chemists, together with researchers from science centres in China, Italy, Lithuania, Switzerland and Luxembourg, significantly improved the stability of perovskite solar cells using the passivation method. The perovskite surface becomes chemically inactive during passivation, thereby eliminating perovskite defects that occur during manufacture. The ensuing perovskite solar cells achieve an efficiency of 23.9% with longterm operational stability (over 1000 h).
“Passivation has been applied in the past, but so far, a two-dimensional (2D) layer of perovskite has been formed on the traditional three-dimensional (3D) perovskite light absorber, making it difficult for carriers to move, especially at higher temperatures. It is critical to avoid this because the solar cells become hot,” says co-author of the invention, KTU chief researcher Dr Kasparas Rakštys.
To address this issue, an international team of researchers conducted a study that estimated the minimum energy required to form 2D perovskites. The surface of the 3D perovskite layer was passivated by different isomers of phenylenediethylammonium iodide synthesised by KTU. These isomers have the same molecular formula but different atoms in space, determining the probability of 2D perovskite formation.
Researchers from the Lausanne Federal Institute of Technology (EPFL) in Switzerland tested the technology and created perovskite solar mini-modules with an active area over 300 times larger than typical, laboratory-tested perovskite solar cells. These mini-modules achieved a record solar energy conversion efficiency of 21.4 per cent. The surface of the perovskite layer of the record-breaking mini-solar modules was coated with materials developed by KTU chemists.
“The study proved to be quite effective in preventing the negative effects of passivation on solar cells. It has been discovered that an isomer with the passivation centres nearest to each other characterises the most efficient passivation. Because of spatial interference, this affects the production of 2D perovskites. Spatial interference is also used as a tool to prevent or slow down negative reactions,” says the KTU researcher.
The invention appeared in one of the most prestigious journals
The findings were published in Nature Communications, one of the world’s most respected scientific journals.
At the moment, KTU researchers are working with colleagues from other countries to produce functional, hole-transporting materials and new perovskite compositions: “International cooperation in science is vital because it is impossible to cover all sectors working in such an interdisciplinary subject as chemistry, physics, and materials science.”
After graduating from MSc in Applied Chemistry at KTU, Dr Rakštys did his PhD in Switzerland, and later an internship in Australia. Today he is working at KTU.
“After spending over 6 years in prestigious foreign research institutions, I decided to realise my scientific ideas in Lithuania, and thus contribute to the successful growth and popularisation of Lithuanian science. I believe that working in your own country can provide more meaning, inspiration and self-realisation. The financial support provided by the MJJ Foundation has contributed significantly to this decision,” says Dr Rakštys.
Researchers at KTU synthesise, test, and aim to apply new materials for the production of more efficient and stable solar cells: “This is a very appealing area because perovskite solar cells are currently one of the fastest-growing technologies, and their successful commercialisation could contribute to climate change solutions,” says Dr Rakštys.
This is not the first time that KTU scientists have set a world record in solar technologies. KTU chemists, together with physicists at Berlin’s Helmholtz-Zentrum (HZB) Research Institute in Berlin, have improved the efficiency of tandem silicon-perovskite solar cells, which now stands at 29.8 per cent. It is a world record for this type of solar element.
