Probing and Manipulating Carrier Interlayer Diffusion in van der Waals Multilayer by Constructing Type-I Heterostructure

van der Waals multilayer heterostructures have drawn increasing attention due to the potential for achieving high-performance photonic and optoelectronic devices. However, the carrier interlayer transportation behavior in multilayer structures, which is essential for determining the device performance, remains unrevealed. Here, we report a general strategy for studying and manipulating the carrier interlayer transportation in van der Waals multilayers by constructing type-I heterostructures, with a desired narrower bandgap monolayer acting as a carrier extraction layer. For heterostructures comprised of multilayer PbI₂ and monolayer WS₂, we find similar interlayer diffusion coefficients of ∼0.039 and ∼0.032 cm² s^-1 for electrons and holes in the PbI₂ multilayer by fitting the time-resolved carrier dynamics based on the diffusion model. Because of the balanced carrier interlayer diffusion and the injection process at the heterointerface, the photoluminescence emission of the bottom WS₂ monolayer is greatly enhanced by up to 106-fold at an optimized PbI₂ thickness of the heterostructure. Our results provide valuable information on carrier interlayer transportation in van der Waals multilayer structures and pave the way for utilizing carrier behaviors to improve device performances.