Inhibition of Amine–Water Proton Exchange Stabilizes Perovskite Ink for Scalable Solar Cell Fabrication

Ambient air processing is desirable for the industrialfabrication of perovskite solar cells. Here, we show that perovskiteink containing methylammonium and formamidinium inN-methyl-2-pyrrolidone andN,N-dimethylformamide, a cosolventcomposition that satisfies prerequisites for upscaling solar cellfabrication, degrades within a day in ambient air. From1H NMRspectroscopic analysis, wefind that water proton exchange withmethylammonium and formamidinium facilitates the aminolysis offormamidinium by methylamine. The addition of elemental sulfurinhibits this proton exchange process via sulfur-amine reactions,resulting in a stable perovskite ink with an extrapolated half-life of6300 h. The control ink aged for 1 day does not form perovskitefilms for solar cell fabrication, while the sulfur-stabilized ink isreproducibly used to make devices with efficiencies >15% when aged for over 1 month. The stabilized ink is suitable for upscalingperovskite solar cell fabrication, with efficiencies up to 17% for blade-coated devices.