Methylammonium-formamidinium reactivity in aged organometal halide perovskite inks
Vitantonio Valenzano, Andrea Cesari, Federica Balzano, Antonella Milella, Francesco Fracassi, Andrea Listorti, Giuseppe Gigli, Aurora Rizzo, Gloria Uccello‐Barretta, Silvia Colella
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.