Unassisted photoelectrochemical water splitting devices based on Cu(In,Ga)Se2 photoelectrode and nanostructure IrOx anode with solar-to-hydrogen efficiency over 10%
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신병하 KAIST Efforts to convert sustainable solar energy into a storable form of chemical fuels have garnered great interest. Among various technologies, photoelectrochemical (PEC) water splitting, which is capable of producing hydrogen fuel in an environmentally friendly manner, is being intensively studied. Because PEC water splitting has an operating principle similar to that of photovoltaic devices, a good photovoltaic (PV) material must be a good candidate for a photoelectrode of PEC solar water splitting. However, a single photoelectrode either cannot provide a sufficient voltage for spontaneous water splitting (for smaller bandgap photoelectrodes) or can only generate a photocurrent density that is too low to be practical (for higher bandgap photoelectrodes). Therefore, a connection of two light absorbers electrically in series (photoelectrode-photoelectrode or photoelectrode-PV configuration) is necessary for a high solar-to-hydrogen (STH) conversion efficiency. In this talk, I will present our group’s recent progress in building PEC-PV tandem devices for unassisted water splitting which consists of a Cu(In,Ga)Se2 (CIGS)-based photocathode, a halide perovskite PV cell, and a nanostructured IrOx anode. All three components of the device have been thoroughly investigated: for the CIGS photocathode, reduced graphene oxide overlayer and ZnS/CdS double buffer layers were applied, which together greatly improved the PEC performance and stability; for the halide perovskite PV, the bandgap was widened to increase the output voltage; for the anode, IrOx-coated porous nanowires were fabricated and they resulted in an exceptionally large Tafel slope and mass activity. These efforts altogether led to an unassisted PEC-PV device with STH exceeding 10%. Technical details will be discussed. |