Epitaxial growth of CH(NH 2 ) 2 PbI 3 thin films on CH 3 NH 3 PbBr 3 single crystal substrates by vapor phase deposition

Metal halide perovskites have shown high potential for opto-electronic devices due to their excellent properties: strong light absorption, long carrier lifetime, and moderate mobilities. The power conversion efficiencies of the perovskite solar cells have reached 25.5%, which are comparable to crystalline Si ones. Most of the current perovskite devices are polycrystalline thin films made by spin-coating. To further enhance the performance of perovskite devices, single crystals and epitaxial growth are necessary. Compared with spin-coating, vapor phase deposition has higher controllability. We have been focusing on the epitaxial growth of crystalline all-perovskite heterostructures using physical vapour phase deposition technique. We have tried to grow CH 3 NH 3 PbI 3 thin films on the CH 3 NH 3 PbBr 3 single crystals by co-evaporation of CH 3 NH 3 I and PbI 2 [1] . However, we obtained only Br-rich CH 3 NH 3 Pb(BrI) 3 alloy epitaxial thin films due to the ion inter-diffusion. Recently, the inter-diffusion free CH(NH 2 ) 2 PbI 3 film was reported to be grown on CH 3 NH 3 Pb(BrCl) 3 alloy substrates by solution method [2] . Inspired by this, here we report the vapor phase epitaxial growth of perovskite thin films by changing the organic cations and its effect on the ion inter-diffusion.