Hybrid perovksites are a material class with uses in various optoelectronic devices. However, some of the compositions with the best optoelectronic properties are also the least stable to temperature, humidity or light. Here Sheng Xu and colleagues report an method of deposition of mixed-cation hybrid perovskite films that serve as lattice-mismatched substrates for an α-FAPbI3 film, enabling a tunable strain gradient within the film. The chemical heteroepitaxial thin-film growth method can give strains of up to 2.4 per cent, while also stabilizing the metastable α-FAPbI3 phase. In the absence of any stabilizing influence, these phases are only stable to phase transformation for a day, whereas in the strained system the authors report stability over several hundred days.
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