Thermal and Structural Characterization of Methylammonium‐ and Formamidinium‐Halide Salts

Four organic halide salts of interest to alloyed perovskite solar cell fabrication are characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), powder X‐ray diffraction (XRD), and thermogravimetric analysis. The chemical and crystal structures of methylammonium iodide (MAI), methylammonium bromide (MABr), and formamidinium iodide (FAI) are confirmed, and the experimental ATR‐FTIR spectrum and XRD pattern of formamidinium bromide (FABr) are presented. The enthalpy, ΔH vap, and entropy, ΔS vap, of vaporization are quantified for each salt and are used to estimate their vapor pressures in the temperature range of 150–300 °C. MAI, MABr, and FAI have similar vapor pressures in this temperature range, whereas FABr has a higher vapor pressure in the temperature range of 150–240 °C. These data provide a foundation for achieving effective control of vapor phase concentrations for vapor processing of alloyed perovskite solar cells.