Band-aligned C3N4−xS3x/2 stabilizes CdS/CuInGaS2 photocathodes for efficient water reduction

Compared with bare CIGS films and CdS-modified CIGS films (CdS/CIGS), C3N4−xS3x/2/CdS/CIGS electrodes exhibit a reduction of 200 mV in the onset potential. They also show a doubled photocurrent at 0 V versus the RHE, and a broadband 20% enhancement of incident photon to current efficiency (IPCE) in noble-metal-free systems. Remarkably, the C3N4−xS3x/2/CdS/CIGS electrode shows ≤5% loss over 20 hours of continuous operation, whereas bare CdS/CIGS shows a rapid degradation within the first 4 hours.