Enhancing the Photocatalytic Hydrogen Evolution Performance of the CsPbI₃/MoS₂ Heterostructure with Interfacial Defect Engineering

Developing highly efficient photocatalysts for the hydrogen evolution reaction (HER) by solar-driven water splitting is a great challenge. Here, we study the atomistic origin of interface properties and the HER performance of all-inorganic iodide perovskite β-CsPbI₃/2H-MoS₂ heterostructures with interfacial vacancy defects using first-principles calculations. Both CsI/MoS₂ and PbI₂/MoS₂ heterostructures have strong binding and dipole moment, which are enhanced by interfacial iodine vacancies (V_I). Because of the nature of type II heterojunctions, photogenerated electrons on the CsPbI₃ side are promptly transferred to the MoS₂ side where HER occurs, and sulfur vacancies (V_S) spoil this process, acting as surface traps. The formation energies of various defects are calculated by applying atomistic thermodynamics, identifying the growth conditions for promoting V_I and suppressing V_S formation. The HER performance is enhanced by forming interfaces with lower ΔG_H values for hydrogen adsorption on the MoS₂ side, suggesting PbI₂/MoS₂ with V_I to be the most promising photocatalyst.