A first-principles study of interfacial vacancies in the β-CsPbI₃/1T-MoS₂ heterostructure towards photocatalytic...

Halide perovskite (HP) composites with transition metal dichalcogenides (TMDs) have attracted attention as promising photocatalysts for hydrogen production through solar-driven water splitting but their working mechanism is yet unclear. Here, we propose novel heterostructures composed of all-inorganic HP β-CsPbI₃ and metallic TMD 1T-MoS₂ and investigate the influence of interfacial vacancies on their interfacial properties using first-principles calculations. Using CsPbI₃(001)/MoS₂(001) interface slab models with a minimal lattice mismatch, we calculate the interface formation and interlayer binding energies, finding that the PbI₂-terminated interfaces have better stability and stronger binding strength than the CsI-terminated ones and iodine vacancy enhances the binding properties. Our calculations demonstrate that photo-generated electrons are transferred from CsPbI₃ to MoS₂, inducing a dipole moment at the interface that prevents recombination of electrons and holes, and this desirable process for the hydrogen evolution reaction (HER) is enhanced by forming an I vacancy. Through analysis of the electronic density of states, we reveal that the I vacancy reduces the band gap of CsPbI₃ by down-shifting its conduction band minimum level and forming a shallow defect state, being favourable for enhancing the HER performance on the MoS₂ surface. This work highlights a way to design advanced photocatalysts based on HP/TMD composites for hydrogen production using solar energy.