Near-Unity-Efficiency Energy Transfer From Perovskite To Monolayer Semiconductor Through Long-Range Migration And Asymmetric Interfacial Transfer

van der Waals heterostructures combining perovskites of strong light absorption with atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) hold great potential for light-harvesting and optoelectronic applications. However, current research studies integrating TMDs with low-dimensional perovskite nanomaterials generally suffer from poor carrier/energy transport and harnessing, stemming from poor interfacial interaction due to the nanostructured nature and ligands on surface/interface. To overcome the limitations, here, we report prototypical three-dimensional (3D)/2D perovskite/TMD heterostructures by combing highly smooth and ligand-free CsPbBr3 film with a WSe2 monolayer. We show that the energy transfer at interface occurs through asymmetric two-step charge-transfer process, with ultrafast hole transfer in similar to 200 fs and subsequent electron transfer in similar to 10 ps, driven by the asymmetric type I band alignment. The energy migration and transfer from CsPbBr3 film to WSe2 can be well described by a one-dimensional diffusion model with a carrier diffusion length of similar to 500 nm in CsPbBr3 film. Thanks to the long-range carrier migration and ultrafast interfacial transfer, highly efficient (>90%) energy transfer to WSe2 can be achieved with CsPbBr3 film as thick as similar to 180 nm, which can capture most of the light above its band gap. The efficient light and energy harvesting in perovskite/TMD 3D/2D heterostructures suggest great promise in optoelectronic and photonic devices.