Solution-Processed Cd-Substituted CZTS Photocathode for Efficient Solar Hydrogen Evolution from Neutral Water

Cu-kesterite has the appropriate optical properties of a photocathode in a solar water-splitting system; however, its performance is limited by poor bulk and surface transport properties. In this work, a photocathode design consisting of solution-processed Cu2Cd0.4Zn0.6SnS4 (CCZTS) photoabsorber coated with CdS/TiMo/Pt is reported to yield a photocurrent of 17 mA cm−2 at 0 VRHE, which is at least 3 times higher than pristine Cu2ZnSnS4. X-ray photoelectron spectroscopy depth profiling and UV photoelectron spectroscopy measurements reveal a deeper valence band maximum for the CCZTS absorber, which results in a “spike-like” 0.13-eV conduction band offset when integrated with CdS. Rotating dipole Hall and femtosecond transient reflectivity measurements revealed an improved mobility and carrier lifetime of the CCZTS absorber. Our investigation shows that the improved photocurrent can be attributed to the improved bulk properties of CCZTS absorber.