Interfacial electric field-driven direct Z-scheme charge transfer in CuCl/SnX (X = S, Se) heterojunctions: First-principles prediction of superior optical absorption, high STH efficiency, and photocatalytic water splitting

Solar-driven hydrogen production is a promising route toward clean energy, yet its efficiency is often limited by poor light absorption and rapid charge recombination. To overcome these challenges, two-dimensional CuCl/SnS and CuCl/SnSe van der Waals heterostructures are designed and systematically investigated. The formation of an intrinsic interfacial electric field enhances charge separation and prolongs carrier lifetimes, leading to improved photocatalytic performance. First-principles HSE06 calculations, together with binding energy, elastic modulus, and ab-initio molecular dynamics analyses, confirm the thermodynamic stability of the heterostructures and reveal a Z-scheme charge transfer mechanism with band edges well aligned for overall water splitting. Moreover, the heterojunctions exhibit significantly enhanced visible-light absorption with a pronounced red shift compared to their individual components. Both heterostructures demonstrate exceptional carrier mobility (∼10³ cm² V⁻¹ s⁻¹) and high solar-to-hydrogen conversion efficiencies of 34.43% for CuCl/SnS and 22.71% for CuCl/SnSe. Near-optimal hydrogen adsorption free energies indicate favorable HER kinetics. Collectively, these results highlight the strong promise of these heterostructures for efficient solar-driven photocatalysis.