Engineering Ultrathin CuxS Layer on Planar Sb₂S₃ Photocathode to Enhance Photoelectrochemical Transformation

Sb 2 S 3 has been extensively used as light absorber for photoelectrochemical cell. However, its p‐type nature may result in the formation of Schottky junction with substrates, thus hindering the collection of photogenerated holes. Herein, an ultrathin Cu x S layer is successfully engineered as the bottom junction for Sb 2 S 3 for the first time. Capitalizing on its impressive electrical properties and superior optical properties, the Cu x S layer exhibits a high work function of 4.90 eV, which causes the upward band bending of p‐type Sb 2 S 3 , forming a hole‐transparent structure with ohmic contact. The transparency of the ultrathin Cu x S layer enables back‐illumination of the Sb 2 S 3 /Cu x S platform, facilitating the integration of intricate catalyst layers for photoelectrochemical transformation. When modified with Pt nanoparticles, the photocurrent density reaches −5.38 mA cm −2 at 0 V vs . RHE, marking a fourfold increase compared to the photocathode without Cu x S layer. When introducing a molecular hybrid TC‐CoPc@carbon black, a remarkable average photocurrent density of −0.44 mA cm −2 at the overpotential of 0 V is obtained for CO 2 reduction reaction, while the photocurrent density is less than −0.03 mA cm −2 without Cu x S.