Development of highly efficient CuIn0.5Ga0.5Se2-based photocathode and application to overall solar driven water splitting†
A CuIn1−xGaxSe2 (CIGS) photocathode having a specific composition exhibited remarkable promotion of hydrogen evolution from water, with a half-cell solar-to-hydrogen conversion efficiency of 12.5%. CIGS thin films with various compositions (defined by x = Ga/(In + Ga)) were prepared via a three-stage method employing a vacuum evaporation system. The photocurrent from CIGS photocathode surfaces modified with CdS and Pt (Pt/CdS/CIGS) significantly increased along with x as a result of a reduction in the conduction band offset at the CIGS/CdS interface. Using an optimized aqueous electrolyte resulted in enhanced photocurrents of 28 and 18 mA cm−2 at 0 and 0.6 VRHE, respectively, under simulated AM1.5G sunlight. A tandem-type PEC cell containing the newly developed CIGS photocathode and a BiVO4 semi-transparent photoanode demonstrated stoichiometric hydrogen and oxygen evolution with a solar-to-hydrogen conversion efficiency of 3.7% without the application of an external bias voltage.