The Applications Of Hierarchical ZnO Nanostructures In Energy Devices

Zn O is an important semiconductor photovoltaic material which has a small absorption in the visible range, having the characteristics of simple synthesis process, and excellent electron transportation, environmental friendly, low toxicity, good stability and low cost. Zn O has many applications, including Light emitting diodes, biosensors, piezoelectric nano-generators, nano-lasers, solar cells, photocatalysis, photolysis of water and other fields, which has been widly concerned. This article demonstrated an inexpensive and effective way to produce large area Zn O nanotree arrays by a two-step electrodeposition and hydrothermal method. Zn O nanotree was applied to polymer solar cells and water splitting. In order to find the best way to improve its water splitting performance and the polymer solar cells properties,the influence of different annealing temperature on the Zn O crystal morphology and water splitting performance was carefully studied. Then different length of the Zn O nanorod and nanotree with titanium dioxide and magnesium oxide processing were discussed, aiming to improve the power conversion efficiency of polymer solar cell. The main contents include the following three aspects:(1) We prepared the primary nanorod by electrodeposition, made the seed layer by sol-gel method on the surface of the nanorod. After calcination, the nanobranches were grown during the hydrothermal reaction. Scanning electron microscope, X-ray diffractometer, were employed to characterize the structures and properties of the Zn O nanorod and nanotree arrays. By comparing the experiments, it was found that the sol aging time played a determinant role in the growth of the nanobranches. Aging treatment can increase the colloidal particle size. After calcination, the seeds reached and even exceeded the critical size required for nucleation. Then, the nanobranches can grow with time during the hydrothermal reaction.(2) Zn O nanotree structure was treated with titanium dioxide and magnesium oxide, and then assembled into organic-inorganic hybrid solar cells.The results showed that 40 min growth of nanorod in the organic-inorganic hybrid solar cells has the best performance, and titanium dioxide treatment for 1h on the Zn O nanotree causes the improvement of VOC and Jsc.,followed by ZnO nanotree having magnesium oxide treatment. The test results showed that 80 min grown nanotree has a large Jsc 9.95 m A cm-2, and the conversion efficiency was increased 1.17 times.(3) Zn O nanotree was used in the water splitting performance test, and Mott-Schottky test, linear sweep voltammetry and Electrochemical Impedance Spectroscopy(EIS) were employed to characterize the structures and properties of the Zn O nanorod and nanotree arrays. Zn O with different temperatures annealing treatment effects its crystal and donor concentration. Annealed and non-annealed of Zn O nanotree at different temperatures have a linear sweep voltammetry test under simulated sunlight, The linear sweep voltammetry measurement shows that the photoelectrochemical(PEC) water splitting property of the Zn O nanotree photoelectrode increased with the annealing temperature, reached the maximum value at 300 oC, then decreased until 550 oC.In the Mott-Schottky, we get a donor concentration of Zn O to obtain space charge layer thickness by further calculations, The degradation of the property was due to the limitation of the space charge layer thickness caused by the small size of the branches on the Zn O nanorod surface., The improvement of the PEC water splitting property was attributed to the improved crystal quality by annealing treatment. Compared to the nanorod photoelectrode, the nanotree electrode possess a much better PEC water splitting property, as a result of much larger surface-to-volume ratios, which enjoy great advantage in PEC water splitting for efficient delivery of photogenerated carriers.In the EIS test, it shows that 300 ℃ annealed of Zn O nanotree has a low recombination probability during transmission, thereby increased the efficiency of electron transfer.