Lead Iodide Perovskite Thin Film Formation: The Impact of Preparation Method Studied by In Situ GIWAXS.

Lead halide perovskite materials have been successfully incorporated as the active layer into novel solar cells, the performance of which depends strongly on the structure and morphology of the perovskite thin film. This applies in particular to perovskites with a mixture of methylammonium (MA+) and formamidinium (FA+) as the A-site cation. Here, we present a thorough analysis of different mixed cation lead iodide perovskite crystallization scenarios using in situ grazing incidence wide-angle X-ray scattering (GIWAXS). We quantify the phase composition, crystallinity and orientational order of perovskite thin films for various preparation methods and the corresponding intermediate precursor phases. Specifically, we investigate one-step conversion (OSC), gas-quenching with nitrogen and antisolvent induced crystallization with three different antisolvents (chlorobenzene (CB), isopropanol (IPA), ethanol (EtOH)). We find that the average grain size is determined already during the formation of the intermediate phases and therefore it strongly depends on the preparation method. The alcoholic antisolvents introduce a more complex crystallization pathway, including new intermediate structures, and a preferred orientation, which is not necessarily retained by the perovskite thin film.