Phase-engineered Non-degenerate Sliding Ferroelectricity Enables Tunable Photovoltaics in Monolayer Janus In2S2Se

TL;DR

This paper introduces phase-engineered non-degenerate sliding ferroelectric phases in monolayer Janus In2S2Se, enabling tunable and enhanced photovoltaic effects through reversible phase transitions and polarization control.

Contribution

It demonstrates the synthesis and phase transition mechanisms of non-degenerate sliding ferroelectric phases in Janus In2S2Se, leading to tunable photovoltaic properties.

Findings

WZ' to ZB' transition increases carrier mobility and induces an indirect-to-direct band gap change.

WZ' phase exhibits superior photoelectric efficiency in visible light.

Distinct photovoltaic behaviors are achieved through phase engineering of ferroelectricity.

Abstract

Two-dimensional sliding ferroelectrics, with their enhanced efficiencies of charge separation and tunability, constitute promising platforms for next-generation photovoltaic devices. However, recent systems predominantly exhibit dual degenerate polarization states with weak intensity, hindering the optimal manipulations of photovoltaic effects through sliding ferroelectricity. Here, we address this limitation by introducing two strengthened and distinct non-degenerate sliding ferroelectric phases (WZ' and ZB') in Janus In2S2Se, which can be achieved by Se-to-S substitution in monolayer In2Se3. First-principles calculations validate the experimental synthesis of this structure and its capability for reversible phase transitions triggered by atomic layer sliding, and a series of superior photovoltaic performances are demonstrated in such unique Janus In2S2Se, accompanied by a detailed analysis of how non-degenerate sliding ferroelectricity modulates distinct photovoltaic characteristics. The WZ' to ZB' transition can increase the carrier mobility and moderate the band gap while inducing an indirect-to-direct transition, yielding a marked red-shift and enhancement of the photocurrent peak in the infrared spectrum. Conversely, the WZ' phase, benefiting from enhanced polarization, delivers superior photoelectric conversion efficiency in the visible light region. This work establishes a phase-engineered framework of how non-degenerate sliding ferroelectricity orchestrates distinct photovoltaic behaviors, and the intrinsic physical correlations may offer novel perspectives for designing and regulating innovative photovoltaic devices.