| Abstract:Type â…¡ core/shell heterostructures with ZnO naorods as core materials and low band gap semiconductor materials as shell can not only promote the effectively separation of photo-generated electron-hole pairs at the interface, but also can broaden the optical absorption covering nearly the entire visible light region. So, type â…¡ core/shell heterostructures applied to solar cells is expected to improve the photoelectric conversion efficiency.In order to improve the quality of the nanorod growth and reduce the production cost, simple liquid technology was adopted to prepare gradient ZnO/ZnxCd1-xSe core-shell composite nanorods and their application in solar cells was studied in this paper. Polystyrene nanosphere were used to build a template to control the orderly growth of ZnO nanorods. ZnxCd1-xSe shells of tunable compositions have been synthesized via a ion-exchange approach to form effective type II heterostructures. Post-annealing was used to further improve the crystallinity of the shells and ZnS was introduced as a passivation layer to suppress light corrosion and improve the stability of solar cells. The main contents include:1. Construction of the periodic template by self-assembled colloidal crystal monolayers. In order to grow more regular ZnO nanorod arrays and increase the carrier mobility, polystyrene nanosphere were used to build a template to control the orderly growth of ZnO nanorods. Three kinds of templates were formed by self-assembling at air/water interface and subsequent transferring to FTO substrate, and followed by sol curing to fill the gap of PS sphere and the final PS removal process.2. Preparation and Characterization of ZnO nanorods. Orderly ZnO nanorods prepared using periodic template by hydrothermal growth. The structure and morphology of ZnO nanorods were characterized by scanning electron microscope (SEM) and X-ray Diffraction (XRD). The best conditions for the ZnO nanrods growth was determined.3. Preparation and Characterization of ZnO/ZnxCd1-xSe core-shell nanorods. ZnO/ZnxCd1-xSe core-shell nanorods were prepared by liquid ion-exchange technology. The structure, morphology and chemical composition of composite nanorods were characterized by scanning electron microscope (SEM), X-ray Diffraction (XRD) and energy dispersive spectroscopy (EDS). The absorbance of ZnO/ZnxCd1-xSe core-shell nanorods were also measured. Comparing with ZnO nanorods, the ZnO/ZnxCd1-xSe core-shell nanorods sample have some changes in morphology and absorbance. It is no longer smooth at the surface of ZnO/ZnxCd1-xSe core-shell nanorods, which have a increased absorption in visible light region. The temperature of liquid ion exchange reaction affected the absorbance of ZnO/ZnxCd1-xSe core-shell nanorods.4. Device fabrication, JV curve measurements and efficiency analysis. ZnO/ZnxCd1-xSe core-shell nanorods on FTO was used as phtoanodes, platinized FTO used as conter electrodes and polysulfide solution used as an electrolyte to fabricate the solar cells. The influence of orderliness, density and thickness of the ZnO/ZnxCd1-xSe nanorod arrays on the photovoltaic performances was evaluated. |
