Bulk photovoltaic effect in MoSe$_2$ and Janus MoSSe sliding ferroelectrics

TL;DR

This study uses first-principles calculations to explore how stacking and chemical asymmetry in MoSe₂ and Janus MoSSe bilayers influence their nonlinear optical and photocurrent responses, revealing new ways to tune light-matter interactions in 2D ferroelectrics.

Contribution

It demonstrates how interlayer sliding and Janus intralayer polarization can be used to control and enhance photocurrent generation in 2D ferroelectric bilayers.

Findings

Photocurrent spectra are similar in bilayers with canceling intralayer polarizations.

Enhanced photoresponses occur when intralayer polarizations add up.

Photocurrent generation is mainly influenced by vertical chemical asymmetry.

Abstract

We present a first-principles study of the nonlinear optical properties of sliding ferroelectric bilayers based on MoSe$_2$ and Janus MoSSe. Two Janus configurations are considered: i) one bilayer where the two intralayer polarizations caused by Janus chemical asymmetry cancel each other out, yielding photocurrent spectra comparable to pristine MoSe$_2$ bilayers; ii) another bilayer where the intralayer polarizations add up, for which the photoresponses are strongly enhanced. Our results show that photocurrent generation in the polar Janus structures is predominantly governed by vertical chemical asymmetry, with limited dependence on the sliding direction. These findings highlight complementary design strategies: interlayer sliding enables sensitivity to external tuning, while the Janus intralayer polarization enhances photoresponses in the visible range. The interplay between composition and stacking therefore provides a versatile platform for tailoring light-matter interactions in 2D ferroelectric materials.