4
RUDN University chemist has found a way to improve solar cells

RUDN University chemist has found a way to improve solar cells

RUDN University chemist discovered four new stable compounds that can be obtained in the reaction of iodine with methylammonium iodide — the use of these substances will allow the production of perovskite solar panels without toxic reagents, and will save manufacturers from by-products.

Lead-based hybrid perovskites are used in modern solar cells as a light-absorbing layer. But they are unstable to moisture, and existing technologies require the use of solutions and toxic solvents. This complicates the technology and makes it potentially dangerous. The solution to the problem can be solvent-free methods, that is, the use of melts rather than solutions — for example, you can apply a polyiodide melt to a thin film of metallic lead. However, there are few reliable studies of polyiodide chemistry. RUDN chemists investigated the properties of methylammonium (CH3NH3) and iodine compounds to find variants of compounds suitable for use in the production of perovskite solar cells.

Compounds of the methylammonium iodide (MAI) and iodine system melt at room temperature and form ionic liquids — melts that are composed exclusively of ions. The use of such liquids, which can be evenly applied to large surfaces, as precursors will bring closer the industrial production of modular solar cells based on hybrid perovskites on an industrial scale.

Already studied polyiodide-based liquids melt at room temperature only in the presence of large organic cations in the composition. RUDN chemist Viktor Khrustalev explained this difference by the fact that the methylammonium cation has a large dipole moment and is capable of forming a large number of hydrogen bonds. For small cation sizes, this leads to increased entropy during melting, which in turn lowers the melting point.

Under certain conditions, crystals of various compositions begin to fall out of the liquid-MAI2, MAI2.67, MAI4 and MAI5.5. In order to determine under what conditions the melt exists, scientists performed calculations of the enthalpy and entropy of the formation of these crystals. For all compounds except MAI2, the reaction of obtaining a compound from iodine and a composition with a lower iodine content proceeded solely due to the entropy contribution. RUDN chemists explained that the increase in enthalpy during the transition to compounds with a higher iodine content is due to the weakening of the interaction of cations with anions due to the distribution of a small negative charge on a large polyiodide anion. A similar increase in entropy is due to the complexity of polyanions and the weakening of the bonds between them.

These thermodynamic data made it possible to refine and generalize the experimental values of the boundaries in which the melt can exist.

Chemists have also found that similar effects occur in similar compounds with the formamidinium cation (FA+ = HC (NH2)2) and polybromides. Moreover, the mixed composition (MABr3) 0.15 (FAI3) 0.85 exhibits the properties of an ionic liquid from −40 to 80 °C. Such a low melting point of the precursor is favorable for the production of thin films of mixed hybrid perovskites, which exhibit maximum light-absorbing properties.

The article was published in Article in The Journal of Physical Chemistry Letters.

Visiting Professors View all
03 Nov 2017
Michele Pagano is a graduate of the University of Pisa, a leading scientist, the author of more than 200 publications in international journals, and a participant in many international research projects
2105
Main Publications View all
15 Nov 2017
RUDN University scientists publish results of their scientific researches in highly-recognized in whole world and indexed in international databases journals (Web of Science, Scopus ect.). That, of course, corresponds to the high status of the University and its international recognition. Publications of June-September 2017 ( In Journals of categories Q1-Q3)
1355
Similar newsletter View all
21 Oct
RUDN University mathematician determined the conditions for the coexistence of three species in the wild

RUDN University mathematician together with colleagues from India and France for the first time studied in detail the system of coexistence of three species of living creatures in the wild. The results help to understand what parameters determine the extinction andли survivalof species, and how the number of species changes in space and time.

25
21 Oct
RUDN University Chemist Created Coordination Polymers Films with up to 99.99% antibacterial efficiency

RUDN University chemist with his colleagues from Portugal has developed two types of coating based on new coordination polymers with silver. Both compounds were successfully tested against four common pathogens.

23
21 Oct
RUDN scientists have improved titanium dental implants with graphene nanosloyers

RUDN researchers have created and tested a method for processing titanium dental implants. It turned out that theanoslos of graphene on the surface of titanium improve its interaction with stem cells,which are placed on the implant so that it better "takes root".Thanks to this method ofprocessing, stem cells are better kept on the surface, multiply and turn into the desired cells.

25
Similar newsletter View all