Perovskite/Graphene Sandwiches—Halide Perovskite Heterostructures with Blocked Anion Diffusion

Halide perovskites exhibit notoriously fast anion diffusion. This intrinsic material property has hindered advancements in the growth of halide perovskite heterostructures APbX₃/APbX’₃ (where X and X’ are different halide species), as the halides quickly diffuse across the heterojunction forming an alloy. This inability to grow heterostructures severely limits the utility of halide perovskites as semiconductors, as they are not at parity with the complex heterostructures accessible with traditional semiconducting materials. Here we present the growth of such halide perovskite heterostructures by depositing single layer graphene in between two perovskite layers, CsPbBr₃ and CsPbI₃. The heterostructure shown, CsPbBr₃/Graphene/CsPbI₃, shows no anion diffusion after being stored in ambient conditions over long periods of time. In contrast, CsPbBr₃/CsPbI₃ deposited sequentially rapidly form alloys of CsPb(Br_3-xI_x). A suite of characterizations convincingly demonstrate that the heterojunction formed is sharp and no apparent halide diffusion occurs. DFT calculations, UPS, and TA spectroscopy show there is a type I band alignment between the perovskites in this system and that the graphene has little effect on the interactions of the two perovskite materials. Furthermore, the deposition process for integrating graphene with halide perovskites is extremely facile and does not require expensive laboratory equipment. As such, we believe this can enable numerous advances in halide perovskite research, across many research groups, including more advanced heterostructure architectures, graphene enhanced perovskite device stability, and fundamental studies on halide perovskite/2D materials research.