In-plane ferroelectric monolayer TlNbX4O and its application in bulk photovoltaic effect

Abstract

A bulk photovoltaic effect (BPVE) in materials without inversion symmetry attracts increasing interest for high-efficiency solar cells beyond the p–n junction paradigm. Herein, we report the photovoltaic effect in an experimentally feasible TlNbX4O monolayer (TlNbX4O-ML, X = Cl, Br, I) with a large ferroelectric polarization. Using first-principles calculations, we demonstrate that TlNbX4O-MLs are ferroelectric semiconductors with moderate switching barriers and higher spontaneous polarizations. Furthermore, we observe fairly giant shift current with the values of 109.6 μA/V2 for TlNbCl4O, 60 μA/V2 for TlNbBr4O, and 56.1 μA/V2 for TlNbI4O. These results unveil distinct features of the BPVE and the potential application of two-dimensional ferroelectric materials for next-generation photovoltaic devices.