Design Synthesis And Photoluminescence,Photoelectric Conversion Properties Of ZnS,ZnO,TiO₂ Micro-nanostructures

In-doped ZnO/GeO₂ core-shell nanostructures, ZnO, ZnS, In₂O₃ micro-nano materials grown on metal (alloy) substrates, and sea urchin-like TiO₂, ZnO micro-nano structures were prepared by the design synthesis. Their formation mechanisms have been analyzed in this thesis. The morphologies and microstructures of the as-prepared materials have been investigated by using of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The room temperature photoluminescence of the products has been studied and analyzed. In addition, the preparation process of the dye sensitized solar cells (DSCs) has also discussed. The as-synthesized TiO₂, ZnO micro-nano structures have been used to fabricate "sandwich" type DSCs devices and the photoelectric conversion performance of them is investigated. The following is the main contents of this dissertation.(1) In-doped ZnO/GeO₂ core-shell nanostructures have been successfully synthesized by one step thermal evaporation of a mixed powder of ZnO, In₂O₃, and GeO₂. The doped ZnO/GeO₂ core-shell nanostructures have a rod-like single-crystalline In-doped ZnO core and an amorphous GeO₂ shell. The doped ZnO/GeO₂ core-shell rods can be assembled into the bird's nest by self-assembly. Detailed analyses indicate that the In-doped ZnO core grows along the <01-11> direction through a vapor-liquid-solid mechanism, where the In-Ge alloy catalyzes the growth of the In-doped ZnO core wich is protected by GeO₂. The room temperature photoluminescence spectrum of the sample is composed of two bands, including a weak violet peak centered at 405 nm (3.06 eV) and a strong green emission centered at 510 nm (2.43 eV), which can be attributed to the Ge-O vacancies and the singly ionized oxygen vacancies.(2) ZnS nanowires with "Z" type bending have been prepared by vapor phase method, where the brass (Cu-Zn alloy) foils with high Zn content were used as the substrate.The growth of the as-synthesized ZnS nanowires follows VLS growth mechanism, where Cu-Zn droplets from the thermal decomposition of alloy substrate are used as the catalyst. Room temperature photoluminescence spectrum showed that the emission spectrum of one-dimensional ZnS nanostructures consist of a center at 2.57eV (482 nm) blue emission peak, a center located at 2.88eV (430 nm) purple peak and a new center at 3.12eV (397 nm) peak.(3) A complex one-dimensional nanostructure-film-metal substrate architecture, which is composed of ZnS nanorods, island-like ZnS film and Zn foil, has been formed via a liquid-phase epitaxial growth mode. The room-temperature photoluminescence spectrum shows that the complex ZnS nanostructures have a strong blue emission band centered at about 423 nm and a weak broad green emission band centered at about 515 nm.(4) Modulated ZnO hierarchical nanostructures have been successfully synthesized by vapor phase method, where Zn foils are used as the substrate.The ZnO hierarchical nanostructures consist of large quantities of high dense nanowires strewn with some small balls which connected with wires by short rods. The composition detection results show that the ball is metallic Zn, which confirms that Zn serves as the catalyst for VLS growth of the ZnO hierarchical nanostructures. The photoluminescence spectrum of the modulated ZnO hierarchical nanostructures includes a weak ultraviolet peak centered at 380 nm and a strong green emission centered at 500 nm.(5) In₂O₃ micro-nano structures have been synthesized by a direct heating mode, where Cu-In alloy foils are used as the substrate. In₂O₃ micro-nano structures have the genetic characteristics. Analysis revealed that Cu-In alloy surface melted and then oxided, which led to the formation of In₂O₃ micro-nano structures.(6) Sea urchin-like TiO₂ micro-nano structures have been synthesized through a simple solvothermal method. The micro-nano structures are composed of TiO₂ microspheres and TiO₂ nanoneedle arrays on the spherical surface. Characterization showed that the nano-needle has a good performance on the crystallization, grows along <110> direction.(7) The as-prepared sea urchin-like TiO₂ micro-nano structures are used as a light anode for dye-sensitized solar cells (DSCs) to form a "sandwich" DSCs device. The short-circuit current density (JSC) of as-prepared battery is 3.83mA/cm², open circuit voltage (VOC) is 0.66V, the fill factor is 49.2%, and the total battery photoelectric conversion efficiency is 1.24%. In addition, TiO₂ nanoneedle/P25 composite film is also used as the anode of the DSCs to discover the effect of TiO₂ nano-needles.(8) Sea urchin-like ZnO micro-nano structures have been directly prepared on FTO conducting glass through a simple heat treatment method. Then, the sea urchin-like nano-structures are treated by the hydrothermal ripening, so that the morphology evolution of one-dimensional structure on the spherical surface occurred. The micro-nano structures are composed of microspheres and the quasi-one-dimensional array structures on the surface of the microspheres. The room temperature photoluminescence spectrum shows that: the photoluminescence spectrum of the sample consists of a center located at 381nm weak UV emission peak and a center at 510nm strong yellow-green emission peak before the ripening. PL spectrum has an only obvious center at 383nm ultraviolet emission peak after the treatment process.(9) The as-prepared sea urchin-like ZnO micro-nano structures have been used as the light anode of "sandwich" type dye-sensitized solar cell. The test of the photoelectric conversion characteristics of the cell which fabaricated by ZnO micro-nano structures before ripening shows that its JSC is 2.60mA/cm², VOC is 0.668V, FF is 49.5%,ηis 0.86%. However, the performance of the cell built by ZnO micro-nano structures after hydrothermal ripening treatment is significantly improved.