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Posted: May 23, 2017
How to obtain highly crystalline organic-inorganic perovskite films for solar cells
(Nanowerk News) Members of the Laboratory of New Materials for Solar Energetics, working at the Faculty of Material Sciences, in cooperation with their colleagues from the Faculty of Chemistry of the Lomonosov Moscow State University have elaborated a new method. It allows to obtain highly crystalline organic-inorganic perovskite films for solar cells. The project results are published in Materials Horizons ("A new formation strategy of hybrid perovskites via room temperature reactive polyiodide melts").
Scientists of the Lomonosov Moscow State University Press Service has already worked on nanowires of hybrid organic-inorganic perovskites, which are treated as a promising substance for creation of light emitting diodes, lasers and photodetectors on their basis.
However, the most promising application area for such substances is elaboration of perovskite solar cells - namely, photovoltaic devices of new generation. Efficiency of these devices has risen by several times over the last five years and now comprises even more than 22%. This is significantly higher than maximum efficiency, obtained for solar cells on the basis of polycrystalline silicon. Efficiency of the most popular solar cells, produced industrially, is 12-15%.
These are microphotos of perovskite films of various morphology obtained by the elaborated technique. (Image: Alexey Tarasov)
At the moment one could distinguish two main approaches to obtaining of such material. The first one implies coating with chemical agents from vaporous state and the second one -- solution crystallization. Projects, aimed at improving these methods, have been intensively developed in recent years. However, further perspectives of these approaches are almost exhausted. In this light elaboration of new techniques for creation of materials, used in photovoltaics, could give fresh impetus in the area development.
Alexey Tarasov, Doctor of Chemistry, the Head of the Laboratory and the Study Lead shares: "As part of the study we've found out several new compounds -- polyiodides, which are liquid at room temperature, possessing unique properties. They look like viscous liquids of dark brown color with metal gleam, obtained from two solid powders, which simply melt while blending. Liquid state of such compounds allows not to use hazard solvents and, moreover, their chemical composition contributes to formation of a necessary perovskite upon contact with a metallic lead film or other lead compounds. As a result of the chemical interaction between a lead film and polyiodide melts, a perovskite film, comprised of large interpenetrating crystals, is formed.
Upon contact of two chemical agent powders at room temperature a viscous dark liquid is formed in a matter of seconds. This is methylammonium polyiodides. (Image: Alexey Tarasov)
Polyiodide melts are deposited on lead by a so called spin coating technique. For this purpose a glass substrate, on which a lead layer is applied by thermal spraying, is fixed on a whirling rod and starts rotating. Polyiodide is spilled on the whirling glass substrate and afterwards polyiodide residue is flushed by a solvent (namely, isopropanol).
As a result you get perovskite films from 200 to 700 nm in thickness. Their stability is determined, for the first place by the material, of which they consist. The members of the Faculty of Material Sciences have shown the possibility to diversify the composition of applied polyiodides and, consequently, the possibility to select a composition with optimal stability.
Alexey Tarasov comments: "A perovskite film exhibit intense photoluminescence and large lifetimes of charge carriers that provides good functional properties. We've also revealed in our project the possibility to obtain perovskite films of various compositions, while using mixed polyiodide compounds. Researches, conducted by our laboratory in the area of perovskite photovoltaics, are funded in the framework of a Federal Target Program of the Russian Ministry of Education and Science together with the industrial partner - EuroSibEnergo Company."
The Laboratory currently continues studying properties of discovered polyiodides and elaborating on their basis a technology, allowing to obtain solar cells with high efficiency.