Janus γ-GeSSe Monolayer as a High-Performance Material for Photocatalysis and Thermoelectricity

Two-dimensional Janus materials have attracted increasing attention in recent years because of their potential as materials for energy applications, such as photocatalysis and thermoelectricity (TE). Here, for the first time, we propose a monolayer Janus structure with the Mexican-hat band, gamma-GeSSe, by replacing the S atoms on one side of the synthesized gamma-GeS with Se atoms. Using first-principles calculations based on density functional theory (DFT), we show that gamma-GeSSe is mechanically, dynamically, and thermally stable. The mechanical, electronic, optical, and transport properties of monolayer Janus gamma-GeSSe are also investigated in the DFT calculations. We find that the ideal strengths of the Janus gamma-GeSSe are 6.08, 8.6, and 10.08 GPa for the armchair, zigzag, and biaxial directions, respectively. The Janus gamma- GeSSe is an indirect-gap semiconductor with a band gap of 1.131 eV. Our results show the Janus gamma-GeSSe as a photocatalysis material for water splitting with a high solar-to hydrogen efficiency of up to 28.78%. This is because the combination of features includes an intrinsic electric field, high optical absorption coefficient, and carrier mobility. In addition, with the gamma-structure, the Janus gamma-GeSSe shows an intrinsic low lattice thermal conductivity of 3.33 W/mK at room temperature, which will contribute to obtaining high TE efficiency. By using the Boltzmann transport theory, we find that the maximum TE power factor and figure of merit of the Janus gamma-GeSSe reach 55-85 mW/mK(2) and 0.7-0.9 in the temperature range from 300 to 900 K, respectively. Thus, our findings not only contribute to proposing a Janus material but also suggest that it can be used as an energy material with high-performance photocatalysis and TE.

Automated summary

A monolayer Janus structure γ-GeSSe with a Mexican-hat band gap is proposed for the first time. Gamma-GeSSe shows mechanical, dynamical, and thermal stability. The material exhibits high-performance photocatalysis and thermoelectricity due to its intrinsic electric field, high optical absorption coefficient, and carrier mobility.