Photocatalytic water splitting and excitonic effects of novel SiS2/SiSe2 heterojunction

Energy crisis and environmental pollution require efficient photocatalysts for hydrogen production through hydrolysis and good photoabsorbers for solar energy conversion. Therefore, we designed a SiS2/SiSe2 van der Waals heterojunction (vdWH) monolayer as a photocatalyst and photoabsorber. Based on first-principles calculations combined with semi-empirical maximally localized Wannier function tight-binding (MLWF-TB) method, it is revealed that SiS2/SiSe2 vdWH is a semiconductor with an indirect band gap characterized by staggered band alignment, which facilitates the separation of electrons and holes , inhibiting electron-hole recombination. Additionally, the excitonic effects play a significant role in describing the linear optical response in these systems, resulting in an exciton binding energy closer to 300 meV and a small optical anisotropy surge. The solar harvesting analysis shows a solar harvesting efficiency closer to 20 % in the vdWH, showcasing performance enhancement when compared with the isolated monolayers. Our theoretical findings shed light on the design of novel nonmetal-based photocatalysts for water splitting and provide useful guidelines for future experiments.