Abnormal thin film structures in vapor-phase deposited methylammonium lead iodide perovskite

The authors report on the observation of abnormal growth features in methylammonium lead iodide thin films synthesized by vapor-phase deposition with high methylammonium iodide (MAI) flux. The morphological and crystallographic impact of varying flux of MAI is characterized using scanning electron microscopy and x-ray diffractometry. It was found that increasing organic flux results in large, angular, yet hollow nonuniformities growing within the film. Diffraction patterns show good perovskite crystallinity across all samples, but show texture development with the (220) diffraction peak growing in intensity relative to the (004) peak as organic content increases. A possible mechanism for the growth of these features is discussed. These results highlight some potential critical pitfalls for perovskite thin film deposition by coevaporation and emphasize the importance of microscopy-based characterization. (C) 2016 American Vacuum Society.