Investigation Of Preparation、characterization And Solar Cells Application Of 3D Micro-nanostructured ZnO Hierarchical Materials

Zine oxide (ZnO), as an n-type semiconductor material with a direct wide-band gap (3.37eV) and considerable excitation binding energy (60 meV) at room temperature, has been extensively studied and applied in piezoelectric transducers, photocatalysts, solarcells, nanolasers, and gas sensors owing to its outstanding optical and electrical properties. On the other side, ZnO is chemically and thermally stable, as well as biosafe and environment friendly. Therefore, micro/nanostructured ZnO have been regarded as fascinating micro/nanomaterials. An increasing number of researchers have expressed keen interest in assembling 1D or 2D nanostructures to form 3D micro/nanostructured materials with special morphologies. These structures may be used as an interesting alternative with higher specific surface area and porosity than those of simple nano structured arrays, which not only possess the outstanding qualities of 3D structures but also specific properties of ID or 2D structures. In this work, we demonstrated a simple hydrothermal method and solvothermal route with mild conditions to grow 3D sea urchin-like hierarchical ZnO films assembled from 1D nanoneedles, 1D nanorods or 2D nanosheets on FTO-glass substrates by using a one step, ammonia-based system. The main rearch work and results were as following:(1) On the basis of previous work, ordered sea urchin-like ZnO nanostructures assembled from 1D nanoneedle array were fabricated via a simple hydrothermal process at relatively mild conditions by one step. The results demonstrated that the optimum reaction time of this 3D micro/nanostructurea was 9 h, and showed the effect of the reaction time on the morphologies of ZnO micro/nanostructures and UV-vis absorption spectra. The sea urchin-like ZnO samples were shown to be typical wurtzite structures with higher crystallinity and were assembled by a central nucleu and many needle-like ZnO which grew radially from the nucleu. Compared with ZnO nanorod arrays, the sea urchin-like ZnO nanostructures showed preferable photoelectric properties as the anode of Dye-sensitized solar cells, which the η was increased 77.6%. This can be attributed to special geometric morphologies.(2) Many kinds of different morphology of ZnO were prepared by solvothermal route in C2H5OH-H2O system with FTO conductive glasses as the base. In the reaction process,3D ZnO micro/nano-sphere assembled from 2D nanosheet was first successfully prepared by adjusting the process parameters. The results demonstrated that the optimum condition of pivotal craftwork of this 3D structures was as follows: alcohol-to-water mole ratio is 1:1, the dosage of NaBH4 is 12 mmol, the reaction temperature is 120℃ and the reaction time is 6 h. Among them, the addition of adjuvant NaBH4 has a induced effect on the specific growth orientation of ZnO nanocrystals. And this kind of 3D ZnO was showed the optimal photoelectric properties. The short circuit current density, open circuit voltage and the photoelectric conversion efficiency are 6.76 mA/cm2,0.692 V,2.09%, respectively.(3) Ordered 3D sea urchin-like hierarchical ZnO micro/nano-sphere assembled from 1D nanorod array was synthesized in a mixture of Zn(CH3COO)2·2H2O, NaBHH4 and NH3H2O (25%) aqueous solution via a simple hydrothermal method by one step. The results demonstrated the effect of the NaBH4, reaction time and reaction temperature on the morphologies of ZnO micro/nanostructures and photoelectric properties. And the optimum condition of synthesis of sea urchin-like hierarchical ZnO micro/nano-sphere was as follows:the dosage of NaBH4 is 48 mmol, the reaction temperature is 120℃, the reaction time is 3 h. Meanwhile, the crystal growth mechanism of 3D sea urchin-like hierarchical ZnO micro/nano-sphere was proposed by tracking the kinds of reaction factors. Among these different morphology of ZnO, the ordered 3D sea urchin-like hierarchical ZnO micro/nano-sphere showed preferable photoelectric properties as the anode of Dye-sensitized solar cells, which attributed to the high porisity, the bigger surface area promoting absorbing more dye. In the growth orientation of nanorods (0001) crystal plane, more effective charge carriers were transmitted and the photoelectric properties was better.