| The control preparation of ZnO nanopowders and ZnO dye-sensitized solar cells have been studyed in this paper.In view of the high cost, complex experimental processes and the difficulty in products'collection in ZnO nanopowders preparation by gas phase method. In this study, ZnO nanopowders were prepared by low-cost hydrothermal and solvothermal synthesis, and by controlling of the experimental parameters to achieve on the morphology control of ZnO and the systematic research on mechanism of morphology controlling has also been done. Several typical ZnO nanopowders have been used to prepare ZnO dye-sensitized solar cells, and the performances of the solar cells were given.Main work and the main results of the paper are as follows:(1)Hydrothermal temperature has great effect on the properties of ZnO nanopowders. Only when hydrothermal temperature was 220℃and the hydrothermal time was over 18h, pure ZnOnanopowder can be obtained. The length of ZnO powders increased with the increaseing of the pH of the hydrothermal synthesis.(2) The type of alcohol had significantly effect on the morphology of ZnO nanopowders. ZnO nanoparticles with diameter～100nm were obtained by using ethanol and isopropanol as a reaction solvent. ZnO nanorods were obtained with the n-butanol, n-hexanol and 1-octanol as the reaction solvent, the grain size distribution broadened with the increasing of carbon chain of alcohol. The mechanism was also discussed in detail. The reaction solvent viscosity increased and the nucleation rate of ZnO decreased with the increasing of carbon chain of alcohol, which resulted in decrease of the initial crystal nucleus and the remaining growth units of [Zn(OH)4]2- gradually deposited on the surface of the nucleus along ZnO (0001) crystal face. At the mean time, reaction solvent viscosity and diffusion resistance of growth units of [Zn(OH)4]2- increase with the increasing of carbon chain,which lead to uneven concentration distribution around the formed nucleus and ZnO nanopowders with a wide size distribution of aspect ratio were obtained.(3)Complexing agent EDTA could increase the length of ZnO nanorods. When the concentration of EDTA was 0.05M, the length of ZnO nanorods was 60μm and diameter was 10μm. When the concentration was 0.1M, the length of ZnO nanorods was 70μm and diameter is 10μm. When the concentrationwas 0.2M, the length of ZnO nanorods was 100μm and diameter was 10μm.(4)Phosphate had great effect on the properties of ZnO nanopowders. Effect mechanism of sodium phosphate on the morphologies of the ZnO nanopowders has been discussed. The operating parameters:the hydrothermal temperature was 220℃. ZnO nanotubes with length 20μm and diameter 4μm were obtained when pure water was used as hydrothermal medium. While ZnO nanosheets with thickness about 100nm were prepared by using sodium phosphate as hydrothermal medium. ZnO nanoparticles with 100nm size were obtained by using 0.1M sodium phosphate ethanol solution or pure alcohol as reaction solution. During hydrothermal synthesis, sodium phosphate ionized completely and formed Na+and PO43-ions. The PO43- ions were adsorbed on (0001) face of ZnO crystal, and the attachment of growth units of [Zn(OH)4]2- onto the (0001) face of ZnO was hindered, which results in the formation of ZnO nanosheets with thickness about 100nm. However, sodium phosphate does not dissolve in ethanol and no PO43-were adsorbed on (0001) face during solventthermal synthesis, which results in the formation of ZnO nanoparticles.(5) Cetyltrimethyl ammonium (CTAB) bromide could regulate the morphology of ZnO effectively.During hydrothermal systhsis, it was found that the sisallike assemblies can be obtained with CTAB concentration in a range of 0.1M-0.5M. With the CTAB concentration used in the synthesis process increasing from 0.1M to 0.5M, the diameter of the nanorod broadens noticeably from 100 run up to 400 nm. Howerve, Only rod-like 1D structures with length of about 8-10μm and width of 200-400 nm were obtained without using CTAB, while with a high concentration of CTAB (0.8M), ZnO nanorods were obtained. During solvothermal systhsis, when CTAB concentration is 0.1M, ZnO nanorods with length of about 800nm, a diameter of about 200nm and aspect ratio of 4:1, were obtained. With the CTAB concentration used in the synthesis process increasing from 0.1M to 0.4M, the diameter of the nanorod broadens noticeably from 200 nm up to 500 nm and the length of the nanorod increase from 800nm to 1000nm.When the CTAB concentration was increased to 0.5M, the resulting ZnO nanopowders with uniform particle size appeared as hexagonal dipyramid. When the concentration of CTAB is 0.8M, some stepped hexagonal crystals and small micopheres coexisted in the product. Detailed views on the shell structure indicate that the ZnO microspheres are comprised of numerous flowerlike building units.(6) PEG is favor for the growth of ZnO nanorods. In solvothermal synthesis, the length and the diameter of ZnO nanorods are 14μm and 4μm when the concentration of PEG is 0.05M, the length and the diameter of ZnO nanorods are 26μm and 8μm when the concentration of PEG is 0.02M. The length and the diameter of ZnO nanorods are 3μm and 300nm when the concentration of PEG is 0.1M and the wolvent is ethanol.(7) The ZnO nanopowders with the diameter of 80nm and 100nm, the ZnO nanosheets with a thickness of 100nm and the ZnO nanorods with the length of 6μm and the diameter of 800nm were used as anode to prepare dye-sensitized solar cell. The particle morphology and the particle size has a great effects on the performance of solar cell. The photoelectric conversion efficiency of solar cell compose of ZnO nanosheets was the lowest, and the maximum one was composed of ZnO nanopowders with the particle size of 80nm. The open circuit voltage, short circuit current, photoelectric conversion efficiencies and fill factor of the obtained battery were 0.681V,10.02 mA/cm2,3.46% and 50.7, respectively, when the ZnOnanometer grain with the particle size of 80nm is used to prepare the anode of the dye-sensitized solar cell.
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