Chalcopyrite Cu(In,Ga)(Se,S) (CIGS) semiconductors are potential candidates for use in photoelectrochemical (PEC) hydrogen generation due to their excellent optical absorption properties and high conduction band edge position. In the present research, CIGS thin film was successfully prepared on a transparent substrate (F:SnO glass) using a solution-based process and applied for a photocathode in solar water splitting, which shows control of the surface state associated with sulfurization/selenization process significantly influences on the PEC activity. A ZnS passivation surface layer was introduced, which effectively suppresses charge recombination by surface states of CIGS. The CIGS/ZnS/Pt photocathode exhibited highly enhanced PEC activity (∼24 mA·cm at -0.3 V vs RHE). The performances of our CIGS photocathode on the transparent substrate were also characterized under front/back light illumination, and the incident photon to current conversion efficiency (IPCE) drastically changed depending on the illumination directions showing decreased IPCE especially under UV region with back illumination. The slow minority carrier (electron) transportation is suggested as a limiting factor for the PEC activity of the CIGS photocathode.

Solar-chemical production is one of the most promising options for producing valuable chemicals from greenhouse gases.

Here, we successfully synthesized a TaN thin film using a simple metal-organic-precursor decomposition process followed by its conversion to nitride and studied its photoelectrochemical (PEC) properties to understand charge separation on the surface. Newly synthesized TaN photoanodes showed a significant difference in the PEC activity in relation to the annealing temperature under ammonia flow, although similar light absorption properties or electronic states were obtained. Charge separation related PEC properties were analyzed using intensity modulated photocurrent density spectroscopy (IMPS) and photocurrent measurements in the absence/presence of scavengers. The charge transfer and recombination rate constants which are related to the photogenerated charge-separation dynamics on the TaN surface were found to be more sensitively influenced by the ammonia annealing temperatures, and low temperature (700 °C) treated TaN showed a fast recombination rate constant (k). In addition, high-efficiency charge injection into the electrolyte on the surface was critically associated with the greatly enhanced photocurrent density of TaN synthesized at a higher temperature (900 °C) of ammonia annealing.