Preparation And Photo-electric Properties Of Ordered Nano-structure Semiconductor Films

Not only due to larger surface area, but superior photoelectric properties ZnO and TiO₂ nano-films have attracted much attention in areas such as dye-sensitized solar cells (DSSC), photocatalysis, chemical sensors, photo-electric detectors, et al. However, the charge transfer in traditional ZnO and/or TiO₂ nano-films consisted of random network nanoparticles is mainly based on inter-particle diffusion, so the efficiency of charge transport is very low; Besides, the wide-band gap nature of ZnO and TiO₂ (Eg≈3.37 eV and 3.2 eV, respectively) limits the absorbance in visible light region. For the improvement of electric transport and the light absorbance the ordered nano-structure films of ZnO and TiO₂ were prepared, and the narrow-band gap CdS (Eg≈2.4 eV) was combined with the ordered nano-structure films, thus the paper mainly includes three parts:(1) Well-aligned ZnO nanorod arrays and the composite film of ZnO/CdS were grown on indium tin oxide (ITO) substrate by chemical solution depositon method. The effects of CdS deposition time on the crystal structure, morphology, photoelectric performance of ZnO/CdS composite film were investigated via X-ray diffraction (XRD), Scanning electron microscopy (SEM), ultraviolet-visible absorption spectrum (UV-vis), photoluminescence spectrum (PL) and surface photovoltage spectrum (SPS), respectively. Our results showed that the absorbance of composite film extended to visible region compared with the bare ZnO nanorod arrays. The SPS also showed a new response region corresponding to the absorption spectrum. We also found that the SPS response intensity of composite film decreased gradually above 383 nm with the increase of CdS deposition time. However, the SPS response intensity increased below 383 nm. We interpreted this phenomenon using two distinct photo-induced charge generation and transfer mechanisms.(2) With using ZnO nanorod array as template, TiO₂ nanotube array film was synthesized successfully based on sol-gel method on ITO substrate. Then the CdS/ TiO₂ composite film was prepared by using the same way to part 1, and the morphology, structure, photoelectric properties of the samples were investigated. The results showed that the thickness of nanotube wall was 20 nm; The absorbance of composite film was enhanced and extended to visible region. The SPS showed that the photoelectric conversion properties of the composite film could be improved when enlarging the surface-to-volume ratio of the nanotubus accompanied with the suitable thickness of CdS deposition.(3) The large area-ordered and single-layer polystyrene sphere (PS) template was prepared successfully, and porous ZnO thin films are made by filling the PS template with precursor sol of ZnO. The PS template and porous ZnO were characterized by SEM,UV-vis,SPM and XRD. The results showed that the PS template was the large area-ordered and face-centered structure; The quality of porous not only depended on the template but the concentration of precursor sol; The thickness of porous ZnO film was 150 nm, and the band gap was 3.18 eV.