Russian scientists have explained the key mechanisms of interaction of hybrid perovskites with solvents. Based on the results obtained, they proposed new approaches to obtaining a light-absorbing layer for solar cells based on perovskites. The results of the work were published in the journal Chemistry of Materials.
To date, thin-film solar cells based on hybrid perovskites have already achieved an efficiency of 23.2%, surpassing traditional solar cells based on silicon. Moreover, the light-absorbing perovskite layer in such devices can be obtained by simpler and cheaper solution methods. Two solvents are usually used to apply thin films of perovskite from solutions: dimethyl sulfoxide and dimethylformamide. However, earlier studies showed that crystallization from these solvents formed intermediate compounds – crystal solvates. They can impair the morphology and functional properties of the perovskite layer.
In a new work, the scientists investigated the crystallization of perovskite from a solvent with unusual properties – gamma-butyrolactone (GBL). It exhibits the so-called retrograde solubility, that is, as the temperature rises, the solubility of perovskite in it decreases. Researchers have widely used this feature to obtain single crystals, and attempts to obtain a thin film often ended with the formation of individual crystallites on the substrate. For a long time, the reasons for this unusual behavior of perovskite solutions in GBL were unknown. It was believed that the interaction between perovskite and GBL is so weak that it does not even form solvates, that is, molecular complexes from the solvent and the solute. However, scientists have found that there are at least three types of GBL perovskite crystal solvates, and some of them have a unique cluster structure. It became clear that the equilibrium in perovskite solutions in GBL is much more complicated than previously thought.
“We have found that at room temperature perovskite dissolves to form such clusters, and when heated, they decompose to small complexes,” said team leader Alexei Tarasov. – This leads to supersaturation and precipitation of perovskite from solution in the form of single crystals. We showed that it was the precipitation of the cluster adduct instead of perovskite that prevented the production of thin films from this solvent, and based on an understanding of the processes occurring during the dissolution of perovskite in GBL, we proposed approaches that direct the crystallization of perovskite bypassing the formation of clusters, which made it possible for the first time to obtain high-quality films from it. This is an excellent example of the practical application of fundamental chemical knowledge to solve applied material science problems – exactly what is commonly called fundamental materials science throughout the world
. ”Source: indicator.ru