A team of researchers from Kaunas University of Technology (KTU), Lithuania, along with ones from Helmholtz Zentrum Berlin (HZB) science institute, Germany, have designed a novel approach to the selective layer formation in perovskite solar cells. The molecule, synthesized by the KTU chemists, assembles itself into a monolayer, which can cover a variety of surfaces and function as a hole transporting material in a perovskite solar cell. This results in a reduction of the amount of materials used in the process, thus reducing costs.

The molecule in this work assembles itself into a monolayer and can evenly cover any oxide surface (including textured surfaces of the silicon solar cells used in tandem architectures. "It's not polymer, but smaller molecules, and the monolayer formed from them is very thin. This, and the fact that the monolayer is being formed through dipping the surface into the solution makes this method much cheaper than the existing alternatives. Also, the synthesis of our compound is a much shorter process than that of the polymer usually used in production of perovskite solar cells", says Ernestas Kasparavičius, PhD student at KTU Faculty of Chemical Technology.

The synthesized material needed testing, so the team from HZB in Berlin, Germany, headed by Dr Steve Albrecht, in collaboration with KTU doctoral student Artiom Magomedov, decided to use this new material as a hole transporting layer in perovskite solar cells.

"In our laboratory in Kaunas we studied use of the self-organizing molecules to form the electrode layer as thin as 1-2 nm, evenly covering all the surface. During my internship in Berlin I was able to apply our material and to produce a first functioning solar element with just a monolayer-thick selective contact", says Magomedov, young researcher at KTU Faculty of Chemical Technology.

Professor Vytautas Getautis, who is the head of the research group behind the invention and the PhD research supervisor of Magomedov, emphasizes the input of the young scientists: "Usually it is so that the seasoned researchers are generating ideas and the youngsters are implementing them. However, in this case the young researchers have both generated the idea and realized it in solar element production".

Using self-assembling monolayer techniques, not only is extremely low material consumption achieved, but also high efficiency - the element's power conversion efficiency was close to 18%, which is exceptionally high for a new technology. Also, when self-assembling monolayer is used as a hole transporting layer in perovskite cells, no additives are needed to improve the performance of the cells. This might significantly improve the life span of the elements. Following their initial success, scientists at KTU are synthesizing new materials for monolayer formation. Initial tests of the optimized materials at HZB have reportedly already led to over 21% efficiency solar cells.



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