Size-effects on shift-current in layered CuInP$_2$S$_6$

TL;DR

This study investigates the size-dependent shift-current response in layered CuInP$_2$S$_6$, revealing a significant reduction in shift-conductivity with increasing thickness and suggesting additional mechanisms contribute to high photocurrent in 2D ferroelectrics.

Contribution

It demonstrates that the shift-current mechanism alone cannot explain the high photocurrent in 2D CuInP$_2$S$_6$, highlighting the importance of size effects and other contributing processes.

Findings

Strong size effect reduces shift-conductivity in bulk limit

Shift-current mechanism alone insufficient to explain high photocurrent

Additional mechanisms likely contribute to enhanced BPVE in 2D ferroelectrics

Abstract

Two-dimensional ferroelectrics have recently emerged as a promising avenue for next-generation optoelectronic and photovoltaic devices. Due to the intrinsic absence of inversion symmetry, 2D ferroelectrics exhibit bulk photovoltaic effect (BPVE), which relies on hot, non-thermalized photo-excited carriers to generate a photo-induced current with enhanced performances thanks to efficient charge separation mechanisms. The absence of a required p-n junction architecture makes these materials particularly attractive for nanoscale energy harvesting. Recent studies have reported enhanced BPVE in nanometer-thick CuInP$_2$S$_6$ ferroelectric embedded between two graphene wafers, driven by relatively strong polarization and reduced dimensionality. Short circuit photocurrent density values have been observed to reach up to mA/cm$^2$. In this paper, we demonstrate that the shift-current mechanism alone cannot fully account for these high conductivity values, suggesting that additional mechanisms may play a significant role. Furthermore, our work confirms the existence of a strong size effect, which drastically reduces the shift-conductivity response in the bulk limit, in agreement with experimental observations.