Effect of monolithic photovoltaic-photoelectrochemical-integrated Cu(In, Ga)Se₂-related co-planar device on water splitting reaction

This study presents the fabrication of a photovoltaic-photoelectrochemical-integrated (PV-PEC) (Cu(In, Ga)Se₂ (CIGS)-related co-planar device (integrated CIGS co-planar water splitting device) that resulted in an onset potential (V _onset) of over 1.23 V to achieve photoelectrochemical water splitting without external bias. Therefore, the utility of this device was indicated for unassisted water splitting reaction. Moreover, the effects of the open-circuit voltage of the CIGS solar cell part on the photocurrent density and V _onset of the fabricated water splitting device were investigated. These results suggest that the applying the reverse bias owing to V _oc of the CIGS solar cell part influences the space charge layer at the surface of the CIGS photoelectrode. This effect leads to the formation of an inversion layer, suppressing surface recombination on the CIGS photoelectrode and contributing to an increase in the photocurrent density. The results represent a preliminary step toward realizing potential applications of the CIGS PV-PEC device for the unassisted water splitting reaction.