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

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 mu A/V-2 for TlNbCl4O, 60 mu A/V-2 for TlNbBr4O, and 56.1 mu A/V-2 for TlNbI4O. These results unveil distinct features of the BPVE and the potential application of two-dimensional ferroelectric materials for next-generation photovoltaic devices.

Automated summary

We report the photovoltaic effect in a feasible TlNbX4O monolayer with large ferroelectric polarization, demonstrating its potential application in high-efficiency solar cells. The TlNbX4O monolayers are identified as ferroelectric semiconductors with moderate switching barriers and higher spontaneous polarizations. Giant shift currents are observed for TlNbCl4O, TlNbBr4O, and TlNbI4O, indicating distinct features of the bulk photovoltaic effect.