| In this paper, we aim at preparing ZnO of different morphologies as the photoanode of dye-sensitized solar cells(DSSCs). We studied the optimality reaction conditions for preparation ZnO and the influence of different reaction conditions on the growth of Zn O. On this basis, we proposed the mechanism for the formation of ZnO nanoaggregates. Besides, we studied the formation of ZnO hierarchical spheres with different sizes. Finally, we applied these ZnO spheres to DSSCs as the photoanode material, and analysed the influence of different ZnO materials on the photovoltaic properties of the DSSCs.On the base of temperature-experiment and time-experiment, we studied the optimality conditions for the hydrothermal reaction with glutamic acid as the construction agent. As a result, the optimality conditions are 150 °C and 10 h. At the same time, with the demonstration of concentration-experiment and time-experiment, we proposed the mechanism of the competition of NaOH and glutamic acid during the growth of ZnO. With the increase of the concentration of NaOH, longer and larger unit would form, and ZnO would grow into nanosheets. If the concentration of NaOH goes on increasing, ZnO would grow into nanorods. On the contrary, the existence of glutamic acid will prevent the tendency of anisotropic growth. With the increase of the concentration of glutamic acid, tiny-rods-assembled spindles would form. Further characterations of Glu-0.5-2, Glu-0.5-3, Glu-1-2 and ZnO nanoparticles(NPs) show that Glu-0.5-2 have larger specific surface area(SSA) than the others except NP, the best crystallinity and the best inner-connection.With different amino acids as the construction agents, we studied the universal rule of the influence of different amino acids on the growth of ZnO. We found the amino acids with different isoelectric point infulenced the growth of ZnO in a regular way. The increase of the concentration of NaOH or the isoelectric point of the amino acid would both result in the formation of nanosheets. On the contrary, the increase of the contration or the decrease of the isoelectric point of the amino acid would result in the formation of tiny-rods-assembled spindles.We applied Glu-0.5-2, Glu-0.5-3, Glu-1-2 and NP as the photoanode material of DSSCs. As a result, Glu-0.5-2 with larger SSA, better crystallinity inner-connection shew to be more suitable as the photoanode material. The DSSC based on Glu-0.5-2 shew the highest efficiency(4.52 %, 21 % higher than that based on NP), the smallest electron-transport-resistance and the longest electron lifetime.We also controlled the size of ZnO hierarchical spheres through changing the dosage of Polyvinyl Pyrrolidone(PVP). It turned out that, with the increase of the dosage of PVP, the average size of ZnO hierarchical spheres increased(from 400 nm to 800 nm), and the SSA decreased accordingly. We applied these hierarchical spheres into DSSCs, and it turned out that the DSSC based on sample 1(400 nm) achieved the highest efficiency. |
