Methylammonium-formamidinium reactivity in aged organometal halide perovskite inks

Abstract

Over the past 10 years, organometal halide perovskites have revolutionized the field of optoelectronics, particularly of emerging photovoltaic technologies. Today’s best perovskite solar cells use triple-cation compositions containing a mixture of formamidinium, methylammonium, and cesium to enable more reproducible and stable device performance. The common procedure uses as-prepared precursor ink to avoid an undesirable decrease in device performance, attributed recently to a chemical reaction between methylammonium and formamidinium in solution. Here we employ nuclear magnetic resonance spectroscopy to explore different experimental conditions that can significantly modify these reaction kinetics; in particular, we find that the presence of cesium as the third cation can substantially slow down methylammonium-formamidinium reactivity. Our findings allow us to draw up a protocol for extended overtime perovskite ink stabilization. Insight into the reactivity of perovskite inks under different experimental conditions Addition of methylamine to formamidinium gives trans / cis N -methylformamidinium Cs + significantly stabilizes the precursor solution by slowing down the reaction NMR is a powerful tool to predict solution modifications prior to device fabrication Halide perovskite inks are unstable over time, which negatively effects photovoltaic device performance. This is due to a reaction between the species in solution, studied here using NMR by Valenzano et al., and the kinetics of this can be tuned by adjusting the components/experimental conditions.