Acid-Catalyzed Reactions Activate DMSO as a Reagent in Perovskite Precursor Inks

• Published in: Chemistry of materials 2019-03, Vol.31 (6), p.2114-2120
• Main Authors: Hamill, J. Clay, Sorli, Jeni C, Pelczer, István, Schwartz, Jeffrey, Loo, Yueh-Lin
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.9b00019

Proton transfer from methylammonium (CH3NH3 +) to dimethylsulfoxide (DMSO), a common Lewis-base solvent, initiates the production of ammonium (NH4 +) and dimethylammonium ([CH3]2NH2 +). We propose two parallel reaction pathways initiated by this proton transfer. Using DMSO-d 6 to elucidate reaction schemes, we demonstrate that protonation is followed either by methyl group transfer between the resulting CH3NH2 and residual CH3NH3 +, or by transmethylation to CH3NH2 from DMSOH+. The former reaction yields NH4 + and (CH3)2NH2 + and is the dominant pathway at processing relevant temperatures; the latter yields (CH3)2NH2 + in addition to methylsulfonic acid and dimethylsulfide. In the preparation of hybrid organic–inorganic perovskite (HOIP) thin films for photovoltaic applications, the substitution of CH3NH3 + with NH4 + and (CH3)2NH2 + in the HOIP crystal results in deviations from the tetragonal structure expected of phase-pure CH3NH3PbI3, with a deleterious effect on the absorptivity of the resulting films. These results emphasize the importance of elucidating the under-appreciated precursor/solvent reactivity, the products of which, when incorporated into the solid state, can have profound effects on HOIP composition and structure, with a commensurate impact on macroscopic properties and device performance.