Controllable Electrodeposition And Photoelectrochemical Properties Of ZnO Nanosutructure Arrays

One-dimensional (1D) ZnO nanosutructure arrays and hierarchical nanosutructure arrays are widely used as photoelectrodes of dye-sensitized solar cells (DSSCs) duo to its unique structural characteristics. In this thesis, ZnO nanostructure arrays with different morphologies were controllably synthesized on different substrates by using a simple electrodeposition method at low temperature. The effects of electrodeposition factors on the preparation and photoelectrochemical properties of as-prepared ZnO nanostructures were discussed in detail.Well oriented single crystalline ZnO nanotube arrays (ZNTAs) with uniform size were successfully synthesized on FTO substrate by one-step electrodeposition method only adjusting the electrolyte pH value lower than7.0, which means keeping the two competitive reactions, namely, ZnO crystal growth and selective self-etching by H+in balance during the electrochemical deposition process. The growth mechanism of the ZNTAs was detailedly discussed and the effects of preparing conditions such as pretreatment of substrate, pH value of electrolyte, electrodeposition potential, concentration of electrolyte, reaction temperature and growth time on the electrodeposition of ZNTAs were systematically investigated. Room temperature photoluminescence and UV-vis absorption spectroscopy were further carried out on ZNTAs to investigate their optical properties and surface intrinsic defect. It was shown that the single crystalline ZnO nanotubes with average diameter smaller than200nm and wall thickness of50nm grew along [001] direction were prepared on FTO substrates when the optimum conditions were:the applied deposition potential was fixed at-1.3V for10s, then the potential was controlled at-1.0V for1800s in the electrolyte of0.005mol L-1ZnCl2and0.1mol L-1KCl with a pH value of3.70. The photoelectric conversion efficiency based on ZNTAs was also measured and an efficiency of0.06%was obtained.ZnO nanorod arrays (ZNRAs) were prepared on flexible stainless steel mesh (SSM) substrate in large-scale by electrodeposition method. The effects of preparing conditions on the electrodeposition of ZNRAs and related photoelectrochemical properties were investigated in detail. It is indicated that the controllable preparation of ZNRAs on SSM substrates was realized. And the relationship between the morphology and the property was preliminarily elucidated. When the times of the electrodeposition from one to three times and the applied potential was controlled at-1.0V for1800s by using the electrolyte of0.005mol L-1ZnCl2and0.1mol L-1KCl solution, the length of rods could be increased from0.8to2.2μm and the overall conversion efficiency of DSSCs based on ZNRAs improved to0.43%.The hierarchical ZNRAs were synthesized on SSM substrate by using a two-step electrochemical deposition, which included the electrodeposition of primary ZNRAs on the substrate, followed by the electrochemical growth of ZnO nanorod branches with an average diameter of-78nm and lenth of-500nm. It is demonstrated that coating the primary nanorod arrays with Zn(CH3COO)2colloid played a key role in synthesising the branched hierarchical ZnO nanostructure. The effects of preparing conditions on the morphologies of hierarchical ZNRAs and the optimal sensitization conditions for the photo-anode were also studied. Compared with primary ZNRAs, it is found that the power conversion efficiency of DSSCs consisting of hierarchical ZNRAs was enhanced from0.43%to0.72%. Finally, by modifying the hierarchical ZNRAs with ZnO nanoparticles and sensitizing at60℃for6h, the DSSC with an overall power conversion efficiency of1.11%was successfully obtained.