g-ZnO/Si₉C₁₅: a S-scheme heterojunction with high carrier mobility for photo-electro catalysis of water splitting

The g-ZnO/Si₉C₁₅ heterojunction is designed, and its stability, electronic properties and photo-electro catalytic properties, and the impact of biaxial strain on the electronic and photocatalytic properties are investigated. The g-ZnO/Si₉C₁₅ heterojunction has a staggered (type-II) band structure (band gap is 1.770 eV), following the S-scheme mechanism. A high electron mobility of 5.113 × 10³ cm² V^-1 s^-1 and hole mobility of 3.324 × 10⁴ cm² V^-1 s^-1 are obtained in the zigzag and armchair directions, respectively. Suitable oxidation and reduction potentials are obtained such that photocatalytic water decomposition can occur at pH = 0-14, and the corrected solar to hydrogen (STH) efficiency is up to 35.4%. The absorption of visible light is enhanced, and the power conversion efficiency (PCE) is 15.1%. The electro-catalytic hydrogen evolution reaction (HER) is more likely to occur at the Si₉C₁₅ interface with a low over-voltage of 0.190 V. Under biaxial strain, due to the controllable band structure, the corrected STH efficiency and PCE increase to 42.7% and 16.7%, respectively. The heterojunction shows potential value in the field of high-efficiency solar devices and catalytic materials for water splitting.