A first-principles study of interfacial vacancies in the β-CsPbI/1T-MoS heterostructure towards photocatalytic applications.

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-CsPbI and metallic TMD 1T-MoS and investigate the influence of interfacial vacancies on their interfacial properties using first-principles calculations. Using CsPbI(001)/MoS(001) interface slab models with a minimal lattice mismatch, we calculate the interface formation and interlayer binding energies, finding that the PbI-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 CsPbI to MoS, 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 CsPbI by down-shifting its conduction band minimum level and forming a shallow defect state, being favourable for enhancing the HER performance on the MoS surface. This work highlights a way to design advanced photocatalysts based on HP/TMD composites for hydrogen production using solar energy.