Controllable Preparation And Property Study Of Ordered CdS Nanostructure

To date, one-dimensional (1D) inorganic nanocrystals have been widelyinvestigated and various nanostructures have been synthesized. However, compared to1D nanostructures, complex three-dimensional (3D) architectures have just beenrealized recently. Meanwhile, ordered 1D inorganic nanocrystals have beenrecognized as potential building blocks for the fabrication and integration of futuregeneration optoelectronic devices. Particularly, inorganic nanocrystal arrays showmuch promising as photovoltaic materials for their high transport mobility and largesurface area. Cadmium sulfide (CdS), as an excellent inorganic semiconductormaterial, has been widely applied in many fileds like nano-catalysts, biotechnology,optics, electronics, etc.. This thesis focuses on developing simple and effectivemethods to synthesize CdS nanocrystals with advanced hierarchy as well as tofabricate ordered CdS nanoarrays on various substrates. The application of thesenanocrystals and nanoarrays hybridized with polymers is also investigated anddiscussed.In chapter 1, the progress on the synthesis of CdS nanocrystals and CdSnanostructured arrays was summarized, and the application of nanocrystals inoptoelectronic fields was discussed.Large-scale and shape-controlled synthesis of 3D flowerlike and branched CdSnanocrystals by hydrothermal process was described in Chapter 2. During thehydrothermal process, cadmium nitrate and thiourea were taken as precursors, andhexamethylenetetramine (HMT) as an organic capping agent. The reaction conditionsinfluencing the synthesis of these 3D CdS nanocrystals like initial precursors' ratio,reaction time, reaction temperature and capping reagent were studied. Themorphology, structure and phase composition of CdS nanostructures were examinedby X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM),energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy(TEM), high-resolution TEM and Raman spectra. The room-temperature photoluminescence (PL) of the obtained CdS nanocrystals was studied. The formationmechanism of the 3D CdS nanocrystals with flower-like structure was proposed basedon the experimental results.Chapter 3 demonstrated a facile two-step approach to fabricate highly-ordered CdSnanorod arrays on transparent conductive substrates by combining electrochemicaldeposition and hydrothermal processes. During the electrochemical depositionprocess, 0.055 mol/L CdCl₂ and 0.019 mol/L sublimed sulfur dissolving in dimethylsulfoxide were used as electrolyte. After electrochemical deposition, the obtained CdSnanoparticle layer was taken as seeds to fabricate CdS nanorod arrays byhydrothermal process. The reaction conditions were optimized by studying theparameters that influence the reaction, such as initial precursors' ratio, reaction time,reaction temperature, etc. Furthermore, the temperature-dependent photoluminescencewas studied. Organic-inorganic hybrid solar cells were fabricated using theas-prepared CdS nanoarrays and poly[2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) (device configuration: ITO/CdS arrays/MEH-PPV/Au). Their photovoltaic behavious were investigated.In Chapter 4, CdS nanorod arrays with a higher aspect ratio than those described inChapter 3 were fabricated using simple one-step approach. Glutathione, a kind ofpeptide, was employed to assist the growth of these nanorod arrays duringhydrothermal process. Several reaction parameters such as reaction time, reactiontemperature and capping reagent, the amount of glutathione were investigated. Theresults showed that glutathione played a key role in the formation of these CdSnanorod arrays. The growth mechanism of the CdS nanorod arrays was also proposedbased on the results. Organic-inorganic hybrids solar cells were fabricated based onthe as-prepared CdS nanoarrays and polymer semiconductors (device configuration:ITO/CdS nanorod arrays-MEH-PPV/Au; or ITO/CdS nanorod arrays-P3HT/Au).Their photovoltaic behavious were compared.In Chapter 5, the method developed in Chapter 3 was introduced to fabricate PbSmicrostructures. Highly symmetric octahedral and truncated-octahedral PbSmicrostructures were fabricated by electrochemical deposition. PbCl₂ and sublimed sulfur dissolving in dimethyl sulfoxide were used as electrolyte for theelectrochemical deposition. These octahedra PbS microcrystals were then employedas seeds for the further overgrowth of PbS microcrystals with a Maya-pyramid(M-pyramid) structure by hydrothermal approach. The formation mechanism of theoctahedron and M-pyramid PdS microcrystals was proposed.