<p>This study focuses on the theoretical calculation of van der Waals heterojunctions for ultraviolet-visible (UV-Vis) broadband photodetection, systematically investigating the geometric, electronic, and optical properties of the MoS₂/Pd₃P₂S₈ heterostructure via first-principles calculations. Three stacking configurations were compared, and Stacking I (A1) was identified to possess the lowest binding energy, thereby exhibiting the highest structural stability. Electronic structure calculations reveal that the heterostructure is an indirect semiconductor with a band gap of 1.79&#xa0;eV and features a type-II band alignment—an essential characteristic that facilitates the spatial separation of photogenerated electron-hole pairs, laying a foundation for efficient photodetection. Analysis of the interlayer spacing shows an equilibrium distance of 3.03&#xa0;Å, and the band gap of the heterostructure can be tuned by adjusting this interlayer spacing. Furthermore, biaxial strain was demonstrated to be an effective means of modulating the band gap and band structure: the type-II band alignment is maintained under compressive strain, while a transition to type-I alignment occurs when the tensile strain exceeds 1%, and the heterostructure exhibits metallic characteristics at a tensile strain of 9%. Optical property studies indicate that the MoS₂/Pd₃P₂S₈ heterostructure achieves a significant enhancement in light absorption within the UV-Vis broadband range, especially in the UV region where its absorption coefficient outperforms those of its individual constituent materials. These findings confirm that the MoS₂/Pd₃P₂S₈ van der Waals heterojunction holds great potential for applications in UV-Vis broadband photodetection and tunable optoelectronic devices.</p>