All-Nanoparticle Self-assembly ZnO/TiO2Heterojunction Thin Films with Remarkably Enhanced Photoelectrochemical Activity

The multilaminated ZnO/TiO2heterojunction films were successfully deposited on conductive substrates including fluorine-doped tin oxide (FTO) glass and flexible indium tin oxide coated poly(ethylene terephthalate) via the layer-by-layer (LBL) self assembly method from the oxide colloids without using any polyelectrolytes. The positively charged ZnO nanoparticles and the negatively charged TiO2nanoparticles were directly used as the components in the consecutive deposition process to prepare the heterojunction thin films by varying the thicknesses. Moreover, the crystal growth of both oxides could be efficiently inhibited by the good connection between ZnO and TiO2nanoparticles even after calcination at 500 °C, especially for ZnO which was able to keep the crystallite size under 25 nm. The as-prepared films were used as the working electrodes in the three-electrode photoelectrochemical cells. Because the well-contacted nanoscale heterojunctions were formed during the LBL self-assembling process, the ZnO/TiO2all-nanoparticle films deposited on both substrates showed remarkably enhanced photoelectrochemical properties compared to that of the well-established TiO2LBL thin films with similar thicknesses. The photocurrent response collected from the ZnO/TiO2electrode on the FTO glass substrate was about five times higher than that collected from the TiO2electrode. Owing to the absence of the insulating layer of dried polyelectrolytes, the ZnO/TiO2all-nanoparticle heterojunction films were expected to be used in the photoelectrochemical device before calcination.