The sliding of van der Waals (vdW) bilayers can induce electric polarization in certain nonpolar two-dimensional (2D) materials. However, this mechanism does not apply to 2D materials with Bravais lattice symmetry (e.g., graphene), where the atomic structure and lattice symmetry have the same point group, preserving inversion symmetry across all stacking configurations. To overcome this limitation, multilayered vdW structures can be exploited for their diverse structural symmetries. In this work, we present a general theory for multilayer stacking ferroelectricity (MSF), which systematically analyzes whether and how different types of polarization can emerge in vdW multilayers composed of 2D materials with Bravais lattice symmetry. This theory clarifies the symmetry evolution during stacking and unifies previous work on sliding ferroelectrics, including tetralayer graphene. Guided by the MSF theory, we design a ferroelectric trilayer ${\mathrm{C}}_3\mathrm{N}$ that exhibits multidirectional in-plane polarization, inducing a strong bulk photovoltaic effect (BPVE) coupled with the ferroelectric order, which is absent in both monolayer and bilayer. These findings highlight the importance of the MSF theory in the design of 2D ferroelectrics for ferroelectric photovoltaic applications.

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• Electric polarization
• 2-dimensional systems
• Ferroelectrics
• Multilayer thin films
• First-principles calculations
• Group theory