Ferroionic heterostructures with reconfigurable free-energy surface and band alignment across CuInP2S6 van der Waals interface with boron nitride and graphene.

Two-dimensional ferroelectric semiconductors with nonvolatile polarization hold great promise for next-generation electronics and photovoltaics. Here, we report reconfigurable band alignment in van der Waals heterostructures based on CuInP2S6 (CIPS) combined with hexagonal boron nitride (h-BN) and graphene (GR), arising from coupled ionic displacement and ferroelectric polarization. Driven by the Cu+ ion-related energy landscape, the ferroelectric polarization order acts as a "pump" that modulates interfacial charge transfer, band alignment configurations, and carrier transport barriers in ferroionic heterostructures. In the h-BN/CIPS stack, polarization switching converts the band alignment from type-H to type-II and reduces the switching barrier to ∼230 meV across the insulating interface. In contrast, in the GR/CIPS heterostructure, it transforms an n-type Schottky barrier into a quasi-Ohmic contact while preserving bistable polarization behavior up to 370 K and producing an asymmetric switching potential with a barrier height of ∼260 meV. These findings highlight the distinct modulation of electronic structure and transport characteristics under different contact environments for ferroionic heterostructures.