Achieving Non-Degenerate Sliding Ferroelectricity via Band-Edge Pinning: A General Design Principle for Controllable Photocatalysis and Photovoltaics

Two-dimensional sliding ferroelectrics, with intrinsic charge separation and enhanced tunability, offering a promising platform for high-efficiency and switchable solar-energy conversions. However, recent systems pre­dominantly exhibit only dual degenerate polarization states with too weak intensity, limiting the optimal manipulations of photocatalysis (PCs) and photovoltaics (PVs) through sliding ferroelectricity. Here, we iden­tify two strengthened and non-degenerate sliding ferroelectric phases (AB and AC) in MoSi2N4/WSi2N4 hetero-bilayer, and uncover how it governs carrier dynamics for enhanced PC/PV activity and efficiency. First-principles calculations demonstrate strong visible-light absorption (∼ 10 ⁵ cm ⁻¹ ), excellent structural stability, and experimentally feasible interlayer sliding between the two phases. Compared to MoSi2N4 homo-bilayer, the enhanced electronegativity contrast between Mo and W atoms pins the band edges of the conduction band minimum (CBM) and the valence band minimum (VBM) to their original layers. As a result, the polariza­tion reversal no longer induces band-edge exchange, resulting in two oppositely driven of the interlayer carrier dynamics. In PCs, the acceptor-to-donor dipole in AC phase can generate stronger redox over-potentials, reduc­ing barriers requirements for spontaneous catalytic activity. Furthermore, this opposite dipole than AB phase shows inhibition effect on the interlayer photo-generated carriers recombination, enabling more free excitons for enhanced solar-to-hydrogen efficiency of 21.3%. In PVs, due to the opposite polarization-driven on charges separation, the AB-to-AC phase transition can also induce enlarged and red-shifted photocurrent, which in turn endows more photo-electronics for the superior photocatalytic behaviors. These findings establish a direct relationship between sliding ferroelectricity and PC/PV performances, and provide a general phase-engineering strategy toward next high-efficiency and controllable solar-energy conversion devices.