Electric-field and strain-tunable electronic and optical response of the van der Waals heterostructure MoS2/HfSi2N4 for green energy applications.

This study explores the van der Waals heterostructure (vdWH) MoS2/HfSi2N4 as a potential candidate material for sustainable energy applications, including optoelectronics, photovoltaics, and photocatalysis. The vdWH MoS2/HfSi2N4 exhibits a small lattice mismatch of ∼2%, indicating exceptional interlayer compatibility. Among the considered stacking configurations, all are stable, with the AE-stacking configuration being the most favorable, exhibiting the lowest binding energy of -0.23 eV. The phonon spectrum reveals the absence of imaginary frequencies across the entire Brillouin zone, confirming the dynamic stability of the heterostructure. These characteristics highlight the vigorous structural integrity, tunability, and synthetic feasibility for next-generation energy-related devices. Electronic structure calculations reveal an indirect band gap of 0.69 eV, which increases to 1.25 eV with the Heyd-Scuseria-Ernzerhof hybrid functional supported by spin-orbit coupling. The band gap exhibits strong sensitivity to an external electric field, such that it increases under positive fields of +0.1 V Å-1 and +0.2 V Å-1, while it decreases under negative fields of -0.1 V Å-1 and -0.2 V Å-1. Such tunable band structure characteristics emphasize the remarkable potential of vdWH MoS2/HfSi2N4 for integration into next-generation photovoltaic and optoelectronics devices. Furthermore, the valence band maxima (VBM) lies below the O2/H2O oxidation potential, demonstrating that the heterostructure is inherently appropriate for oxidizing H2O to O2. However, the vdWH MoS2/HfSi2N4 can perform the hydrogen evolution reaction (HER), satisfying the thermodynamic requirements for water splitting under the s-scheme with and without strain. The band gap can be further modulated through biaxial strain. Tensile strains of +1% and +2% lead to an increase in the band gap, reaching values of 1.38 eV and 1.45 eV, respectively. In contrast, compressive strains of -1% and -2% reduce the band gap to 1.01 eV and 1.19 eV. These strain-induced variations in the electronic structure have a pronounced impact on the optical response of the vdWH MoS2/HfSi2N4. Overall, the excellent electronic and optical properties position the vdWH MoS2/HfSi2N4 as a potential material for future electronic, optoelectronic, and catalytic applications.