Methylammonium Polyiodides: Remarkable Phase Diversity of the Simplest and Low-Melting Alkylammonium Polyiodide System

Andrey A Petrov; Sergey A Fateev; Yan V Zubavichus; Pavel V Dorovatovskii; Victor N Khrustalev; Irina A Zvereva; Andrey V Petrov; Eugene A Goodilin; Alexey B Tarasov

doi:10.1021/acs.jpclett.9b02360

Methylammonium Polyiodides: Remarkable Phase Diversity of the Simplest and Low-Melting Alkylammonium Polyiodide System

J Phys Chem Lett. 2019 Oct 3;10(19):5776-5780. doi: 10.1021/acs.jpclett.9b02360. Epub 2019 Sep 17.

Authors

Affiliations

¹ Laboratory of New Materials for Solar Energetics, Department of Materials Science , Lomonosov Moscow State University , 1 Lenin Hills, 119991 Moscow , Russia.
² Federal Research Center Boreskov Institute of Catalysis , Lavrentiev Ave. 5 , 630090 Novosibirsk , Russia.
³ National Research Centre "Kurchatov Institute" , 1 Acad. Kurchatov Sq. , 123182 Moscow , Russia.
⁴ Inorganic Chemistry Department , Peoples' Friendship University of Russia (RUDN University) , 6 Miklukho-Maklay Str. , 117198 Moscow , Russia.
⁵ N.D. Zelinsky Institute of Organic Chemistry RAS , 47 Leninsky Prosp. , 119991 Moscow , Russia.
⁶ Institute of Chemistry , Saint-Petersburg State University , 26 Universitetskii prospect , 198504 Saint-Petersburg , Russia.
⁷ Department of Chemistry , Lomonosov Moscow State University , 1 Lenin Hills, 119991 Moscow , Russia.

PMID: 31510748
DOI: 10.1021/acs.jpclett.9b02360

Abstract

Newly discovered methylammonium polyiodides (MAI_x) are unique precursors for innovative solvent-free technologies in perovskite photovoltaics because MAI_x are liquids at room temperature and demonstrate high chemical reactivity. We investigated the features of an MAI-I₂ system and built up a first phase diagram in wide temperature and composition ranges using data from differential scanning calorimetry, single-crystal X-ray diffraction, and visual thermal analysis. The phase diagram has been found to differ drastically from that of any related systems owing to the unique propensity of methylammonium toward forming a diversity of polyiodides with complicated crystal structures, namely, MAI₂, MAI_2.67, MAI₄, and MAI_5.5, found in this system for the first time. The performed density functional theory calculations revealed the crucial role of entropy contributing to the formation of higher methylammonium polyiodides, in good agreement with experimental data.