| As an outstanding representative of the third generation semiconductor, Zinc Oxide (ZnO) has been widely used in the field of optics, electronics, magnetics and electrochemistry due to its excellent comprehensive performance, good stability and easy preparation characteristics. With a direct band gap of 3.37 eV and large exciton binding energy of 60 meV at room temperature, ZnO is a high efficient material for short wavelength optoelectronic, which can be used for short wavelength light emission and optical detection device fabrication, and is expected to achieve the room temperature or high temperature stimulated emission. ZnO has a potential application prospect in photovoltaic and photocatalytic due to its excellent electrical transport properties. ZnO has a variety of nanostructures, including one-dimensional nanorods and aligned nanorod arrays. And the properties of these ZnO nanostructures are different from the bulk ZnO. Furthermore, by surface modification and coating, they can be easily constructed as composite nanostructures, such as core/shell nanostructure, which can further control the properties of the material. The research object of this paper is one-dimensional ZnO nanorod arrays and the ZnO/ZnSe and ZnO/CdS core/shell nanorod arrays based on them. On the basis of the successful preparation of the samples, the significant optical properties for photovoltaic and photocatalytic application were studied, and a preliminary attempt was made to some of the photovoltaic application.ZnO nanorod arrays were fabricated by combination of pulsed laser deposition (PLD) and hydrothermal reactions, and their luminescent properties were studied. ZnO thin films were deposited by electron cyclotron resonance (ECR) plasma assisted pulsed laser deposition (ECR-PLD), which were then used as seed layers for aligned ZnO nanorods growing in hydrothermal solution after annealing. By screening and optimizing the preparation conditions, the ideal ZnO nanorod arrays with an average diameter of 50 nm and 1 μm length were obtained. Moreover, the ZnO nanorod arrays had regular morphology, uniform size and neat arrangement. They were c-axis preferred orientation and hexagonal wurtzite crystalline structure. The as-prepared ZnO nanorod arrays had good UV emission properties, and the related internal mechanism of luminescence was studied by variation of the temperature.The core/shell nano-heterogeneous arrays with ZnO nanorod arrays as the core and ZnSe as the shell were fabricated by ZnO nanorod surface coated with ZnSe. The function of the ZnSe shell for inhibition of radiative recombination and broadening of the light response spectrum was studied. ZnSe was deposited on the hydrothermally grown ZnO nanorods by PLD, and then the ZnO/ZnSe core/shell nano-heterogeneous were obtained. ZnO core belonged to the hexagonal wurtzite structure with preferred orientation of c-axis, while ZnSe belonged to the cubic zinc blende structure. The ZnO/ZnSe core/shell nano-heterogeneous showed the typical properties of the core/shell material of type II. The light response spectrum was significantly broadened, not only the absorption edge which related to the band gap of ZnO and ZnSe, but also the absorption of the effective band gap formed by the overlap of the band of ZnO and Znse was observed. The light emission of ZnO was greatly quenched, which reflected that the recombination of light-generated carriers in ZnO was effectively constrained due to the space charge separation of ZnO/ZnSe structure. Both the UV emission related to ZnO near band edge and the blue light related to ZnSe near band edge emission were observed, as well as the visible light resulted from the effective band gap.Similarly, ZnO/CdS core/shell nano-heterogeneous arrays were fabricated by coating CdS on the hydrothermally grown ZnO nanorods by PLD, using ZnO as the core and CdS as the shell. The ZnO core and the CdS shell were both hexagonal wurtzite. The optical properties of ZnO/CdS nano-heterogeneous exhibited the characteristics of the type Ⅱ core/shell heterogeneous material formed by ZnO and CdS. They not only showed a UV absorption edge corresponding to the band gap of ZnO and CdS, but also displayed an absorption of the effective band gap formed by the band gap overlap of ZnO and CdS. The light response spectrum was extended to the near IR band whose band gap was lower than CdS. Similarly, the recombination of the carriers in ZnO was effectively restrained due to the separation of electrons and holes attributed to the CdS coating. As a result, the light emission of the ZnO nanorods was greatly quenched. And these effects will be prominent by improving the structure of ZnO and CdS, as well as the interface of ZnO/CdS.In addition, we also attempted to research the photovoltaic application of the ZnO nanorod arrays and core/shell nano-heterojunction arrays based on ZnO. As a cathode buffer layer, the effect of ZnO films on the properties of solar cell was investigated by fabrication of prototype polymer solar cell and test of the device working performance. ZnO can effectively collect and extract the electrons and block the holes, which can reduce the recombination of electrons and holes to some extent. Moreover, as the optical spacer and oxygen barrier, ZnO buffer layer can sill enhance the stabilities and lifetimes of the devices, and finally to improve the overall device performance. To carry out the application on the nanorod arrays in polymer batteries, the emphasis was put on the optical absorption properties of the composite structure compose of ZnO nannorod arrays, ZnO/ZnSe core/shell nano-heterogeneous arrays or ZnO/CdS nano-heterogeneous arrays and P3HT:PCBM. All of these three composite structures had intensive light absorption in the ultraviolet (UV) to near nfrared wave band. Considering the excellent space charge separation properties of ZnO/ZnSe and ZnO/CdS core/shell structures, they can be expected to improve the efficiency of the polymer solar cell. |
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