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

Abstract

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, γ-GeSSe, by replacing the S atoms on one side of the synthesized γ-GeS with Se atoms. Using first-principles calculations based on density functional theory (DFT), we show that γ-GeSSe is mechanically, dynamically, and thermally stable. The mechanical, electronic, optical, and transport properties of monolayer Janus γ-GeSSe are also investigated in the DFT calculations. We find that the ideal strengths of the Janus γ-GeSSe are 6.08, 8.6, and 10.08 GPa for the armchair, zigzag, and biaxial directions, respectively. The Janus γ-GeSSe is an indirect-gap semiconductor with a band gap of 1.131 eV. Our results show the Janus γ-GeSSe as a photocatalysis material for water splitting with a high solar-tohydrogen 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 γ-structure, the Janus γ-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 γ-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.

Two-dimensional SPdAZ2 (A = Si, Ge; Z = N, P, As) monolayers with an intrinsic electric field for high-performance photocatalysis

“…Due to the smallest band gap of the SPdSiAs 2 monolayer, it has the highest STH efficiency, up to 36.65%. Such a high theoretical STH efficiency of SPdAZ 2 monolayers is higher than that of 2D γ-GeSSe (28.78%), 83 Pd 4 S 3 Se 3 (30.1%) 84 and In 2 Te 3 (32.1%) 33 monolayers. Therefore, the SPdAZ 2 monolayers exhibit great potential for achieving economic production of hydrogen from photocatalytic water splitting.…”

“…As mentioned above, high light absorption abilities of these monolayers are beneficial for high STH efficiencies, which can be calculated according to previous studies. 33,83,84 Before calculating the STH efficiencies, one first needs to obtain the overpotentials χ (H 2 ) and χ (O 2 ) of the HER and OER, respectively, which characterize the redox capabilities of carriers. χ (H 2 ) and χ (O 2 ) could be obtained by calculating the difference between the CBM and H + /H 2 , and VBM and H 2 O/O 2 potential, respectively, whose values are given in Table 4.…”

Investigating the Optoelectronic and Thermoelectric Properties of CdTe Systems in Different Phases: A First-Principles Study

“…Another transport parameter that is used to examine the material proficiency is the figure of merit ( ZT ). To evaluate the effectiveness of thermoelectric nature in these studied phases, the dimensionless figure of merit ( ZT ) is computed and is expressed as follows: , Z T = 0.25em S 2 σ κ normall + κ normale T …”

Strong out-of-plane piezoelectricity and Rashba-type spin splitting in asymmetric structures: first-principles study for Janus γ-Sn2OX (X = S, Se, Te) monolayers

“…By replacing the top layer of S atoms with a layer of Se atoms, Thanh et al proposed the Janus g-Ge 2 SSe monolayer based on the synthesized g-GeS structure. 19 The Janus g-Ge 2 SSe has been theoretically predicted to be structurally stable 19 and can be experimentally synthesized since Janus MoSSe has actually been successfully synthesized before. 20 Due to the breaking of mirror symmetry, 2D Janus nanomaterials possess novel physical characteristics in comparison to their pristine symmetric structure, such as the out-of-plane piezoelectric effect.…”