Fabrication, characterization and photoelectrochemical properties of CdS/CdSe nanofilm co-sensitized ZnO nanorod arrays on Zn foil substrate.

The photoelectrochemical (PEC) performance of ZnO is restricted by its low light absorption ability and high recombination rate of photogenerated carriers. In order to overcome these drawbacks, ZnO/CdS/CdSe heterostructures are prepared on Zn foil substrate using facile three-step methods containing hydrothermal growth, successive ionic layer adsorption reaction (SILAR) and modified chemical bath deposition (CBD). The effects of process parameters containing the number of SILAR cycles of CdS, sensitization sequence of CdS and CdSe, and precursors of CdSe on PEC performance of ZnO/CdS/CdSe heterostructures, and ZnO NRAs on PEC performance of CdS/CdSe co-sensitizer have been scrutinized. Through CdS and CdSe co-sensitization, a layer of CdS/CdSe nanofilm is conformally deposited on ZnO nanorod arrays (NRAs) observed by transmission electron microscopy (TEM). Both the visible-light absorption ability and separation efficiency of photogenerated carriers of ZnO NRAs are significantly enhanced evidenced by UV-vis diffuse reflectance absorption spectra, photoluminescence (PL) spectra and electrochemical impedance spectra. Due to the synergistic effect of ZnO NRAs and CdS/CdSe co-sensitizer, the ZnO/CdS/CdSe heterostructures with five SILAR cycles and one modified CBD cycle (ZnO-CdS5-CdSe) show efficient PEC properties with photocurrent density of 6.244 mA/cm at -0.2 V vs Ag/AgCl under light illumination of 100 mW/cm, which are 57.28 and 4.73 times higher than those of pristine ZnO NRAs and CdS/CdSe clusters, respectively. Moreover, the photoconversion efficiency and incident photon to current conversion efficiency (IPCE) of the ZnO-CdS5-CdSe photoanode reach 4.381% and 80.92%, respectively. The heterostructures based on Zn foil substrate in this study can be a promising candidate for practical PEC application and other applications such as photocatalytic degradation and solar cell due to its low manufacturing cost, large-scale production and efficient PEC ability.