The Preparation And Characteirzation Of CdS Quantum Dots Sensitized ZnO/TiO₂Core/Shell Nanorod Arrays Photoanodes

Semiconductor quantum dots （QDs） can enhance the utilization of sunlight greatlydue to a lot of their attractive advantages, such as quantum size effect and multipleexciton generation. Quantum dot sensitized solar cells （QDSSCs） based on QDs haveattracted intensive attention, because their theoretical energy conversion efficiencycan reach66%which is more than double that of conventional solar cells. Highlyordered, single-crystalline ZnO nanorod arrays （NRAs） would be the most desirablenanostructure used as the photoanodes of QDSSCs due to their efficient chargeseparation and transport properties. In this dissertation, CdS QDs sensitized ZnONRAs photoanodes were fabricated, and the effect of the CdS QDs thickness and ZnONRAs surface passivation on the photoelectrochemical performance of thephotoanodes was investigated. The main results were given as follows:（1） Vertically aligned ZnO NRAs were fabricated by a facile hydrothermal methodon fluorine-doped tin oxide （FTO） transparent conductive glass, and ZnO/CdSphotoanodes were prepared by in situ depositing CdS QDs on ZnO through asuccessive ionic layer adsorption and reaction （SILAR） method. Then, the effect ofthe SILAR precursor concentration and number cycles on the incidentphoton-to-current conversion efficiency （IPCE） was investigated. The experimentresults showed that CdS broadened the visible light area for absorption and enhancedthe utilization rate of the sun energy. Meanwhile, the charge-injection efficiency(η_inj)increased due to the formation of II-type semiconductor heterojunction at theZnO/CdS interface, leading to an improvement of IPCE. IPCE increased and thendecreased with the increase of cycle number at the precursor concentration of0.05M.Before10cycles, ZnO/CdS heterojunction interface increased with the increase ofcycle number, which raised the effective separation of the electron and hole. Inaddition, the increase of CdS QDs enhanced the light harvesting efficiency（LHE）, andIPCE increased gradually. After10cycles, IPCE began to fall with the furtherincrease of cycle number, which was caused by poor η_inj and charge-collectionefficiency(η_cc)with the additional increased amount of CdS QDs.（2） ZnO/TiO₂core/shell NRAs structure was fabricated by magnetron sputtering aTi layer on ZnO followed by post-oxidation treatment. And ZnO/TiO₂/CdSphotoanodes were prepared by in situ depositing CdS QDs through a SILAR method.Then, the effect of the TiO₂shell layer on the photoelectrochemical performance of the photoanodes was investigated. The experiment results showed that the TiO₂shelllayer can effectively passivate the surface defects of ZnO NRAs, leading to animprovement of the photocurrent, IPCE and the electron lifetime of ZnO/TiO₂/CdSphotoanodes. It can be attributed to three reasons: firstly, the TiO₂shell layerdecreased the surface traps of ZnO nanorods and hence suppressed the chargerecombination, leading to an improvement of η_cc. Secondly, the TiO₂shell layerintroduced an energy barrier between ZnO and TiO₂and prevented photoinjectedelectrons from transferring back to CdS, which also contributed to the increase of η_cc.Finally, LHE of the photoanodes were improved by the facilitated CdS QDsdeposition due to the rough surface of the TiO₂shell.