Achieving non-degenerate sliding ferroelectricity via band-edge pinning: an instructive design principle for controllable photocatalysis and photovoltaics

Abstract

Two-dimensional sliding ferroelectrics provide an ideal platform for solar-energy conversion because the intrinsic charge separation and enhanced tunability. However, most existing systems exhibit only dual-degenerate polarization states with insufficient polarization strength, limiting robust control of photovoltaic and photocatalytic responses. Here we predict two enhanced, non-degenerate sliding-ferroelectric phases, AB and AC, in a MoSi₂N₄/WSi₂N₄ heterobilayer, and uncover how they drive distinct interlayer carrier dynamics for controllable solar-energy conversion behaviors. First-principles calculations demonstrate their strong visible-light absorption (~ 10⁵cm⁻¹), high structural stability, and experimentally accessible interlayer sliding. Unlike the MoSi₂N₄ homobilayer, the enhanced electronegativity contrast between Mo and W pins the band edges to their original layers, preventing CBM/VBM exchange under polarization reversal and generating opposite driven of the interlayer carrier dynamics between the two phases. In photocatalysis, the AC phase provides stronger redox driving forces, whereas the AB phase more effectively suppresses interlayer electron-hole recombination and yields higher solar-to-hydrogen efficiency. In photovoltaics, the AB-to-AC transition induces an enhanced and red-shifted photocurrent. These findings establish a direct relationship between non-degenerate sliding ferroelectricity and photovoltaic/photocatalytic responses, thereby providing an instructive phase-engineering strategy toward next high-efficiency and controllable solar-energy conversion devices.