Effect of the energy band bending on surface by Cu-poor layer of Cu(In, Ga)Se₂-related photoelectrode for water splitting

To achieve the field of photoelectrochemical water splitting, the modulating of the valence band maximum (VBM) grading on the surface of Cu(In, Ga)Se₂ (CIGS) photoelectrodes via the deposition of additional In and Se (forming Cu-poor-CIGS layer) following CIGS growth was investigated. The resulting downshift of the Fermi level was likely to occur around the surface of the CIGS films for modulating the VBM grading, increasing the onset potential of the CIGS-related photoelectrodes. Moreover, a hole-blocking layer was obtained via modulated VBM grading of the CIGS-related photoelectrode, which increased the photocurrent density of the CIGS-related photoelectrode. Subsequently, a Cu-poor-CIGS/CIGS interface was formed for modulating the VBM grading using Cu-poor-CIGS, which contributed to increasing the photocurrent density owing to the enhancement of charge separation by the depletion layer in the Cu-poor-CIGS/CIGS interface. This study shows that water splitting can be effectively improved by modulating the VBM grading on the surface of CIGS-related photoelectrodes.