First-principles prediction of SiS-Al ₂ SO and blueP-Al ₂ SO vdW heterostructures for high-efficiency photocatalytic water splitting with 23.67% solar-to-hydrogen conversion

The increasing demand for renewable energy solutions underscores the importance of photocatalytic water splitting as a sustainable technology. In this study, we employ first-principles density functional theory (DFT) to investigate the structural, electronic, optical, and photocatalytic properties of SiS-Al₂SO and P-Al₂SO van der Waals (vdW) heterostructures. We systematically evaluate multiple stacking configurations to determine the most stable interface structures. Our analysis shows that the stacking-a and stacking-c arrangements demonstrate the lowest binding energies for the SiS-Al₂SO and P-Al₂SO systems (model-I and II), confirming their superior thermodynamic stability. The HSE06 hybrid functional, including vdW corrections, confirms that model-I exhibits a direct bandgap, whereas model-II possesses an indirect bandgap. Our electronic structure analysis reveals that both heterostructures exhibit type-II band alignment, enabling efficient charge separation. Complementary charge density difference and electrostatic potential analyses confirm the presence of built-in interfacial electric fields, which further enhance carrier separation while effectively suppressing recombination. Phonon dispersion and <i>ab initio</i> molecular dynamic (AIMD) simulations confirm the dynamic and thermal stability of both models. Optical characterization, as determined by dielectric function and absorption spectrum analyses, reveals strong light absorption at energies above 2 eV. This prominent optical response, combined with their favorable electronic properties, positions these heterostructures as promising materials for optoelectronic devices and photocatalytic applications. Furthermore, the favorable band edge alignment with respect to water redox potentials and calculated solar-to-hydrogen (STH) efficiencies 22.58% for SiS-Al₂SO model-II and 23.67% for P-Al₂SO model-II suggest excellent potential for photocatalytic water-splitting. These results highlight the promise of SiS-Al₂SO and P-Al₂SO heterostructures as next-generation materials for sustainable hydrogen production.