Ammonia-assisted vapour transport deposition of formamidinium salts for perovskite thin films

Formamidinium (FA) cations commonly used in perovskite semiconductors tend to form sym-triazine when sublimed in vacuum, a process that hampers the deposition process. Here we find that ammonia, when used as a carrier gas for formamidinium halides transport, cleaves the sym-triazine ring back to formamidinium, hence enhancing the deposition efficiency.