Two-dimensional (2D) Janus monolayers, distinguished by their intrinsic vertical electric fields, emerge as highly efficient and eco-friendly materials for advancing the field of hydrogen evolution reactions (HER). In this study, we explore, for the first time, the potential viability of the oxygenation phase of two-dimensional Janus transition metal dichalcogenides MoOX (X = S, Se, and Te) monolayers as an exceptionally efficient photocatalyst for hydrogen production. Based on first-principles computations, we demonstrate that all three monolayers exhibit semiconductor behavior, characterized by a band gap ranging from 0.66 to 1.55 eV. This narrow band gap renders the proposed materials highly efficient at absorbing light within the visible region. Excitingly, the introduction of an electrostatic potential difference ΔΦ has granted us the ability to surpass the conventional bandgap limit (E_g≥1.23). Consequently, all monolayers exhibit favorable band alignment with respect to the vacuum level. Moreover, the calculated solar-to-hydrogen efficiency for the envisaged monolayer exceeds the established theoretical limit. Particularly, the MoOTe monolayer emerges as an infrared-light-driven photocatalyst, demonstrating a remarkable solar-to-hydrogen efficiency limit of up to 25,21% when considering the entire solar spectrum. A thorough examination of the Gibbs free energy differences across these monolayers has revealed that the values during the oxygenation phase are significantly smaller and approach the optimum, in contrast to the parental two-dimensional Janus transition metal dichalcogenides. Our results conclusively establish that the proposed materials exhibit exceptional efficiency as photocatalysts for hydrogen evolution reactions. Notably, their efficacy is demonstrated even in the lack of co-catalysts or sacrificial agents.

Through a density functional theory-driven survey, a comprehensive investigation of two-dimensional (2D) Janus aluminum-based monochalcogenides (Al₂XY with X/Y = S, Se, and Te) has been performed within this study. To begin with, it is established that the examined phase, in which the Al-atoms are located at the two inner planes while the (S, Se, and Te)-atoms occupy the two outer planes in the unit cell, are energetically, mechanically, dynamically, and thermally stable. To address the electronic and optical properties, the hybrid function HSE06 has been employed. It is at first revealed that all three monolayers display a semiconducting nature with an indirect band gap ranging from 1.82 to 2.79 eV with a refractive index greater than 1.5, which implies that they would be transparent materials. Furthermore, the monolayers feature strong absorption spectra of around 10⁵ cm⁻¹ within the visible and ultraviolet regions, suggesting their potential use in optoelectronic devices. Concerning the photocatalytic performance, the conduction band-edge positions straddle the hydrogen evolution reaction redox level. Also, it is observed that the computed Gibbs free energy is around 1.15 eV, which is lower and comparable to some recently reported 2D-based Janus monolayers. Additionally, the thermoelectric properties are further investigated and found to offer a large thermal power as well as a high figure of merit (ZT) around 1.03. The aforementioned results strongly suggest that the 2D Janus Al-based monochalcogenide exhibits suitable characteristics as a potential material for high-performance optoelectronic and thermoelectric applications.

Owing to their ecological integrity, non-toxicity, and outstanding performances, Double-Halide perovskites have been vigorously promoted as sustainable alternatives for thermoelectric and photovoltaic applications. In this context, we have systematically explored the structural and mechanical strength characteristics of Cs₂AgGa(Cl,Br)₆ materials through the tolerance factor analyses and Born stability criteria. Subsequently, a detailed study of their electronic, optical, and thermoelectric properties has been performed. As results, both Cs₂AgGaCl₆ and Cs₂AgGaBr₆ show semiconducting nature with a direct bandgap of about 2.57 eV and 1.42 eV, respectively. Additionally, with such desirable band gaps, the optical properties were examined based on the complex dielectric function. It has been derived that both materials exhibit a very high absorption spectrum in the order of 10⁵ cm⁻¹ and a low reflectivity not exceeding more than 18% in the visible and UV region. Furthermore, the Cs₂AgGaBr₆ has been taken into account as absorber to construct the planar p-intrinsic-n structure (FTO/TiO₂/Cs₂AgGaBr₆/Spiro-OMeTAD/Au) and a high-record efficiency of 32.57% has been reached. The thermoelectric performance was also studied and revealed a very high Seebeck coefficient (thermo-power) and a sufficient figure of merit (ZT). Based on these results, we believe that the studied double-halide perovskites present outstanding performance for both optoelectronic and thermoelectric engineering devices.

Computational design of new two-dimensional materials constitutes an effective and promising approach in the development and exploration of a wide range of emerging applications such as optoelectronics, photocatalysis, energy storage, and conversion. Within the framework of this work, we systematically investigated for the first time, the structural, stability, optoelectronic, and pho-tocatalytic properties of new predicted Al(Ga, In)STe monolayers derived from Janus Aluminium mono-chalcogenides through Density Functional Theory and Ab-Initio molecular dynamic simulations. After a full optimization of both struc-tures, their dynamics and thermal stability was confirmed through the calculations of phonon spectrum and ab-initio molecular dynamics at a chosen temperature, respectively. Subsequently, the electronic and optical properties were explored and findings revealed that both monolayers exhibit a semiconducting characteristic with a direct and indirect electronic band gap of about 2.23 and 2.69 eV using HSE06 hybrid functional for AlGaSTe and AlInSTe monolayers, re-spectively. Furthermore, the optical absorption indicates a strong absorption of light in the range between 3 and 18 eV. More noticeably, Both Janus monolayers considered exhibiting a promising optical absorption in the visible wavelength region with an absorption coefficient greater than 10⁵ cm⁻¹. In addition, the photocatalytic properties of these structures were investigated by plotting the band edge positions straddle the reduction potential of H₂ and the oxidation potential H₂O. Based on our results, we conclude that both monolayers offer good thermodynamic stability allowing them to be processed experimentally and can be used as very appropriate candidates for optoelectronics and photocatalytic applications.

Halide-based double perovskites have recently been promoted as high-performing semiconductors for photovoltaic and thermoelectricity applications owing to their outstanding efficiency, non-toxicity and ecological stability. In the framework of this research, we have systematically investigated the structural, mechanical, electronic, optical, and thermoelectric properties of Rb₂InSb(Cl,Br)₆ double halide perovskites. Based on Born stability and tolerance factor criteria, we have found that Rb₂InSb(Cl,Br)₆ are mechanically and structurally stable. Furthermore, we have performed a comprehensive evaluation of the electronic, optoelectronic, and thermoelectric characteristics. From the electronic band structure results, Rb₂InSbCl₆ and Rb₂InSbBr₆ exhibit direct semiconducting band gaps of 1.41 ​eV and 0.53 ​eV, respectively. The optical parameters of Rb₂InSb(Cl,Br)₆ reveal that our active structures have a higher dielectric constant, with maximum absorption in the visible range reaching over 5.68 ​× ​10⁵ ​cm⁻¹ and high optical conductivity (2.19 fs⁻¹ for Rb₂InSbCl₆ and 2.14 fs⁻¹ for Rb₂InSbCl₆). Moreover, the maximum limited spectroscopic efficiency reaches an impressive value of approximately 28.0% for Rb₂InSbBr₆ and 33.7% for Rb₂InSbCl₆. The thermoelectric properties were accurately calculated using the BoltzTraP simulation package. The obtained results reveal a significant electrical conductivity, a strong Seebeck coefficient (S ​≈ ​2756 μVK⁻¹ ​at 300 ​K), and an average figure of merit close to one for both structures (ZT ​≈ ​1). Our findings suggest the versatility of these materials and could be used for a wide range of applications, including commercial solar cells and thermoelectricity.

Hydrogen production via solar light-driven water dissociation has been regarded as an artificial and effective process to overcome the environmental problem as well as solving the current energy crisis. In this regard, numerous works have mainly been devoted to developing the appropriate photocatalyst which satisfies the conditions for water splitting and understanding the photocatalysis process. In this study, we propose for the first time the potential application of the two-dimensional Janus aluminum oxysulfide Al₂OS as an efficient photocatalyst material for hydrogen-production H₂ through the first-principles calculations. Janus Al₂OS monolayer has been designed from the parental binary aluminum sulfide AlS by substituting one sub-layer of sulfide atoms (S) to oxygen atoms (O). The electronic properties of the pristine AlS and the derived Janus Al₂OS were computed using GGA-PBE and HSE06 functionals. According to the band structure, AlS monolayer shows a semiconductor behavior with an indirect bandgap of 2.14 eV whereas, the Janus Al₂OS exhibits a direct bandgap of 1.579 eV. Motivated by the desirable bandgap of the Janus Al₂OS, the absorption-coefficient of Janus Al₂OS shows strong visible light harvesting compared to the parental AlS. Furthermore, the photocatalytic performance of Al₂OS has been investigated. Our calculations demonstrate that the band edge position of Al₂OS is suitable for the hydrogen evolution reaction (HER). More importantly, based on the reaction coordinate, it was found that the Gibbs free-energy ΔG_H^∗ of Al₂OS is 0.97 eV which is smaller than of the two-dimensional Janus Ga₂XY (X, Y = S, Se, Te with X ≠ Y) reported recently. Moreover, this value decreases from 0.97 eV to 0.69 eV under 0.5 V/Å of an external electrical field. Our results indicate that Janus Al₂OS fulfills the fundamental requirements for efficient photo-catalyst under visible light and provides new guidance for hydrogen-production via water splitting.

Two-dimensional materials provide new opportunities for the next generation of effective and ultrathin photovoltaic solar cells. Herein, we propose Janus monolayers of Tin monochalcogenides, especially Janus Sn₂SSe (type TA) and SnGeS₂ (type TB) nanosheets, as strong absorber candidates for solar energy conversion, referring to their excellent electronic and optical properties. Interestingly, based on the first-principles computations, both Janus Sn₂SSe and SnGeS₂ monolayers possess semiconductor character with indirect and moderate band gaps of 1.60 and 1.61eV, respectively. Accordingly, the considered systems, Sn₂SSe and SnGeS₂ single-layers, have high absorption coefficient, reaching up to 49.7 and 62.5μm⁻¹, high optical conductivity of about 4513 and 3559Ω⁻¹cm⁻¹, as well as low reflectivity never exceed 34.6 and 38.5% in visible region, respectively. Additionally, the maximum photovoltaic efficiency of single-junction solar cells based on SnGeS₂ and Sn₂SSe nanosheets can reach as high as 27.47% and 28.12%, respectively. The present outstanding results would motivate both theoretical and experimental researchers to deepen the study of the potential applications of two-dimensional Janus materials based on Tin monochalcogenides in solar cell technology.

During the last decade, Inorganic Halide Double Perovskite materials have attracted widespread interest as a promising eco-friendly and non-toxic alternative to lead based hybrid halide organic–inorganic perovskites materials, with outstanding Stability, Structural and electronic properties. In this study, First-Principles density functional theory (DFT) calculations were performed on the structural, stability, electronic and optical properties of the transition metal-based double perovskites materials Cs₂InGaX₆ (X = Cl, Br, or I). Our results reveal that all these materials exhibit excellent thermodynamic and structural stability owing to their negative formation energies and Goldsmith's factors. It is also observed that Cs₂InGaCl₆, Cs₂InGaBr₆, and Cs₂InGaI₆ materials exhibit band gaps calculated by different functional (GGA-PBE and TB-mpj) in visible-range between 0.89 and 3.24 eV. Furthermore, the computed optical properties reveal strong absorption in UV, visible, and IR range with high optical conductivity and low reflectivity. These obtained results predict that the three transition metal-based double perovskites materials carries promising application in nano-electronic and optoelectronic device applications and can be considered as photovoltaic absorber materials.

The massive consumption of traditional fossil fuel like oil, coal and natural gas has led to serious environmental issues, which drove the search for cleaner renewable energy sources. One such option is photocatalytic water splitting that has attracted much attention as a viable process for the large scale production of hydrogen as a renewable fuel. Within this perspective, we methodically studied the structural, optoelectronic, and photocatalytic properties of two-dimensional aluminum monochalcogenide monolayers with the chemical formula AlX (X = O, S, Se, and Te) based on the framework of Density Functional Theory (DFT). All considered structures are full relaxed and their thermodynamic stabilities are confirmed by computing the phonon spectrum and Ab Initio Molecular Dynamics (AIMD) simulations. The electronic characteristics are also performed on the basis of both exchange correlation functional GGA-PBE and HSE06 in order to obtain the accurate electronic band gap. According to our calculations, all the four monolayers posses indirect band gaps ranging between 1.937 and 2.46 eV. Furthermore, based on desirable electronic band gaps, the optical performance features were further explored including complex refractive index, absorption coefficient and energy loss function by means of the complex dielectric function. It is found that all the four materials present a high absorption coefficient in the visible and Ultra-Violet regions. Finally, the band edge positions of our monolayers straddle the reduction potential of H₂ and the oxidation potential H₂O. Also, it was found that the Gibbs free energy of 2D AlO monolayer is 0.02 eV at certain applied external electric field and very close to ideal catalysts which suggest that the AlO monolayer is better candidate for hydrogen production. Our findings demonstrate that AlX monolayers are suitable materials for optoelectronics and hydrogen production via photocatalytic water splitting.

In the present study, the combination of the First-principles density functional theory (DFT) calculations and Monte Carlo (MC) methods are investigated on the structural, magneto-electronic and magneto-caloric properties of the anti-perovskite carbides Mn₃XC with X = Sn, Zn. Firstly, the electronic band structure and total/partial density of state of both Mn₃SnC and Mn₃ZnC are computed and compared to other theoretical and experimental works. Our results reveal that both Mn₃SnC and Mn₃ZnC structures exhibit a metallic behavior and the valence (VB) and conduction (CB) bands overlap considerably. Additionally, the magnetic and magneto-caloric properties including heat capacity (C), the entropy change (ΔS), adiabatic temperature (ΔT) and the refrigerant capacity (RC) were studied under the magnetic field ranging between 0 and 5 T for both anti-perovskites. Our findings suggest that both anti-perovskite carbide (Mn3SnC and Mn3ZnC) can act as an effective substrate for magnetic refrigeration.