Dark Color ZnO Grown By Hydrothermal Method And The Modulation Of Their Optical Properties

Efficient use of solar energy is one of the most active areas of research.In the process of developing solar energy,people found that only a small part of the solar energy irradiated on the earth’s surface can be effectively utilized.Therefore,how to maximize the use of solar energy is the primary problem to realize the practical application of solar energy.As a broadband gap semiconductor material,ZnO has the potential to absorb full spectrum light energy,thus has a bright prospect to improve the efficiency of solar energy utilization.However,the absorption efficiency of ZnO in visible light is very low.Some scientists are trying to find ways to adjust its band gap,usually by doping other components,to increase the absorption of the sun in the whole spectrum.In our article,we have successfully produced black ZnO materials by traditional hydrothermal synthesis.By changing the temperature,the color of ZnO samples can be gradually changed from gray to brown,and finally to black.The morphology and optical properties of the prepared ZnO samples were systematically studied by SEM,TEM,X-ray diffractometry,UV-vis spectroscopy,and PL spectroscopy.The research results obtained are as follows:1.External conditions affecting the color of ZnO materials during hydrothermal preparation were discussed,including growth temperature,heating time,the additive amount of hydrogen peroxide and the concentration of NaOH solution.The final SEM results showed that with the increase of temperature and the prolongation of heating time,the color of ZnO samples changed from gray,brown to dark black.However,the color of ZnO samples did not change significantly with the change of the amount of H2O2 and the concentration of NaOH.Therefore,by exploring the growth conditions,we have found a way to control the color of ZnO samples.2.The results of UV-vis showed that the higher the growth temperature is,the lower the average reflectivity of ZnO samples to light in the range of 200-1000 nm is,and the lowest is 3.114%at 200 ℃.Moreover,the effect of growth temperature on the average reflectivity of ZnO samples showed a linear change basically,and the similar results are obtained in prolonging the growth time.However,the amount of hydrogen peroxide and the concentration of NaOH solution had no significant effect on the absorption of ZnO.The experimental results are in line with the change of appearance color of ZnO samples.3.From the results of SEM and XRD,we conclude that the ZnO nanorod tip structure is the main reason for its black color,and it can adjust the growth temperature to obtain ZnO samples of different colors.It can be seen that the ZnO nanorods obtained at different temperatures were all hexagonal prism structure,but with the elevation of growth temperature,the top of the ZnO nanorods changed from flat hexagonal to sharp tip.In addition,in the temperature range of 120-170 ℃,the process of tip sharpening of ZnO nanorods can be clearly observed,that is,the existence of hexagonal pyramid platform can be observed.XRD results also showed that the peak strength of(110)lattice plane increases with the improvement of temperature.However,after prolonging the growth time,the shape of the top of ZnO nanorods did not change significantly;when the dosage of hydrogen peroxide and the concentration of NaOH solution were adjusted,the top of ZnO nanorods was usually a flat hexagon,and there was no obvious change.