Favorable band alignment induced by CdxZn1−xS buffer layer in CuInS2 photocathodes for efficient solar hydrogen production

Photoelectrochemical water splitting offers a promising route for sustainable hydrogen generation. However, interfacial band alignment issues, particularly unfavorable “cliff-like” conduction band offsets (CBOs), limit the efficiency of heterojunction photocathodes like CdS/CuInS2 by promoting carrier recombination. This study addresses this critical challenge by introducing a CdxZn1−xS buffer layer, synthesized via a facile chemical bath deposition, to replace conventional CdS. The engineered CdxZn1−xS/CuInS2 heterojunction exhibits a highly advantageous “spike-like” CBO, effectively raising the energy barrier against carrier backflow and significantly suppressing interfacial recombination losses. The optimized Pt/TiO2/CdxZn1−xS/CuInS2 photocathode achieves an exceptional photocurrent density of 30.0 mA/cm2 at 0 V vs reversible hydrogen electrode (RHE) and a peak applied bias photon-to-current efficiency of 4.73% at 0.28 V vs RHE. This work demonstrates a rational band offset engineering strategy using CdxZn1−xS to unlock the high potential of CuInS2-based photocathodes for efficient solar hydrogen production.