Researchers at Lomonosov Moscow state University have designed a new method that allows to obtain highly crystalline organic-inorganic perovskite films for solar cells.
Currently, two main approaches are used for obtaining such materials. The first one involves coating with chemical agents from a vaporous state and the second one is solution crystallization. "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", a team member explains.
Polyiodide melts are deposited on lead using a 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.
The team comments: "A perovskite film exhibits 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 the properties of discovered polyiodides and elaborating on their basis a technology, allowing to obtain solar cells with high efficiency.