Ma, ChunqingT. Eickemeyer, FelixLee, Sun-HoKang, Dong-HoKwon, Seok JoonGratzel, MichaelPark, Nam-Gyu2023-04-102023-04-102023-04-102023-01-1310.1126/science.adf3349https://infoscience.epfl.ch/handle/20.500.14299/196775WOS:000933946800004A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI3) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, the degradation mechanisms are revealed; a strong water adhesion following an elongated lead-iodine (Pb-I) bond distance is observed, which leads to a d-phase transition on the (100) facet. Through engineering, a higher surface fraction of the (111) facet can be achieved, and the (111)-dominated crystalline FAPbI3 films show exceptional stability against moisture. Our findings elucidate unknown facet-dependent degradation mechanisms and kinetics.Multidisciplinary SciencesScience & Technology - Other Topicssurfacesfilmstext::journal::journal article::research article