Fabrication and photoelectrochemical activity of hierarchically Porous TiO₂–ZnO heterojunction film

For the first time, we report the fabrication of hierarchically (macro with nested meso) porous nanocrystalline TiO₂–ZnO heterojunction film onto fluorine-doped tin oxide-coated glass substrate by colloidal crystal templating technique using poly(methyl methacrylate) (PMMA) spheres as template. Accordingly, the precursor solutions of titanium isopropoxide and zinc acetate dihydrate in the presence of Pluronic P123 were used to impregnate the individual solution into the template. Initially, nanocrystalline TiO₂ inverse opal mesoporous film was deposited using the titanium precursor. The film was cured at 450 °C in an air atmosphere. A similar process was adopted to deposit nanocrystalline ZnO inverse opal mesoporous film onto the TiO₂ to obtain hierarchically porous TiO₂–ZnO heterojunction nanocrystalline film. Morphology of the fabricated films showed a periodic arrangement of macropores, whereas the microstructural analysis confirmed the presence of nested mesopores in the film network. Chemical interaction existed between TiO₂ with ZnO forming the heterojunction film was ascertained by X-ray photoelectron spectroscopy. Light harvesting efficiency of the samples was studied, and the photoelectrochemical (PEC) performance of the hierarchically porous heterojunction films as photoanode showed about 5 times enhancement in photocurrent density compared to the pristine metal–oxide–semiconductor film under visible light exposure. The porous nanocrystalline hierarchically porous inverse opal heterojunction film could be used as an efficient photoanode in PEC cell.