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

摘要

Four organic halide salts of interest to alloyed perovskite solar cell fabrication arecharacterized using attenuated total reflectance Fourier transform infraredspectroscopy (ATR-FTIR), powder X-ray diffraction (XRD), and thermogravimetricanalysis. 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 formamidiniumbromide (FABr) are presented. The enthalpy, Δhvap, and entropy,Δsvap, of vaporization are quantified for each salt and are used to estimate theirvapor pressures in the temperature range of 150–300 °C. MAI, MABr, and FAIhave similar vapor pressures in this temperature range, whereas FABr has ahigher vapor pressure in the temperature range of 150–240 °C. These dataprovide a foundation for achieving effective control of vapor phase concentrationsfor vapor processing of alloyed perovskite solar cells.