First-principles study on enhancing the photocatalytic hydrogen evolution performance in Cs₃Bi₂I₉/MoS₂ heterostructure with interfacial defect engineering

Hydrogen has been attracting continuously growing interest as a highly efficient and clean energy source for replacing fossil fuels in the future, and thus developing highly efficient photocatalytic materials for hydrogen evolution is much desirable. In this work, we study the structural, electronic and optical properties of heterostructures composed of the bismuth-based vacancy-ordered iodide double perovskite Cs₃Bi₂I₉ and a two-dimensional dichalcogenide 2H-MoS₂ monolayer without and with a vacancy defect using first-principles calculations. Our calculations demonstrate that the Cs₃Bi₂I₉/MoS₂ heterostructures are energetically stable and induce an interfacial dipole moment, which is beneficial for the prevention of charge carrier recombination. Due to the proper band-edge alignment and the smallest Gibbs free energy difference for hydrogen adsorption, the defective interface with a Cs-vacancy (V_Cs) is found to be the most promising for photocatalytic hydrogen evolution. Moreover, we find that the interfacial V_Cs defect can be formed favourably under the I-rich/Cs-poor condition, where V_I and V_S formations are suppressed. This work provides a way to develop high-performance photocatalysts based on heterostructures composed of the Bi-based halide perovskites and transition metal dichalcogenides for hydrogen evolution from solar-driven water splitting.