Solution-Phase Controlled Synthesis Of Cu-Based Binary And Ternary Selenide/Telluride Nanocrystals And Their Properties Investigation

Recently, Cu-based binary/ternary chalcogenides have been widely applied in solar cell, thermoelectric conversion, biomedicine and other fields due to their unique physical and chemical properties. In addition, as new functional materials, semiconductor-metal heteronanostructure possessing new properties induced by the heterointerfaces have also attracted wide attentions. It is well-known that the properties of materials are significantly influenced by their composition, structure, morphology and size. Thus, development of novel synthetic strategies to investigae the growth mechanism and to prepare the specific target product is of great significance to improve the material performances and applications. The goal of this dissertation is controllable synthesis of Cu-based binary/ternary chalcogenides nanomaterials by a hot-solution injection method, and to explore their growth mechanism and properties, the main parts of the results are summarized as follows:1. Uniform size and monodisperse Cu2-xSe nanocrystals with octahedral morphology are first prepared by a colloidal hot-solution injection method from the reaction of diphenyl diselenide with anhydrous copper chloride, in which oleylamine and 1-octadecene are used as the surfactant and solvent, respectively. The octahedral Cu2-xSe nanocrystals are confirmed to be the cubic phase through the characterizations of the X-ray diffraction, electron microscopy, and compositional analysis. The effects of reaction temperature, reaction time, and capping surfactant of oleylamine on the prepared nanocrystals have been investigated systematically. The growth mechanism of the Cu2-xSe nanocrystals is proposed. In addition, the I-V behavior of the as-synthesized octahedral Cu2-xSe nanocrystals has also been explored and it is found that these nanocrystals are promising candidates for application in photodetecting yields.2. We have developed a solution phase route for the synthesis of ternary CuFeSe2 nanocrystals. High-quality, uniform shape and size, monodisperse CuFeSe2 nanocrystals with quasi-cubic morphology have been successfully synthesized for the first time by a colloidal hot-solution injection method employing copper(Ⅱ) acetylacetonate, iron(Ⅲ) acetylacetonate and diphenyl diselenide as precursors in oleylamine and oleic acid. The characterizations of X-ray diffraction, electron microscopy, compositional analysis confirm that the resulting CuFeSe2 nanoparticles are of tetragonal with an average size of-18 nm. Moreover, the shape of the CuFeSe2 nanoparticles can be tuned from quasi-cubes to quasi-spheres by adjusting the reaction parameters. Optical and photoelectric measurements demonstrate that the as-synthesized CuFeSe2 nanocrystals have strong absorption in vis-NIR regions, suggesting their potential applications in photovoitaic devices as a promising light-absorbing material. Magnetic measurement reveals that the CuFeSe2 nanocrystals are ferromagnetic and paramagnetic at 4 and 300 K, respectively.3. Cu2SnSe3-Au heteronanostructures have been fabricated for the first time via a facile seed-mediated growth method. Optical measurement reveals that such new Cu2SnSe3-Au heteronanostructures exhibit enhanced and broadened optical absorption in vis-NIR region. Moreover, such behavior enhances the optoelectronic and photocatalytic properties of the Cu2SnSe3-Au heteronanostructures. In order to explore its mechanism in the process, we investigated the band structures between Cu2SnSe3 and Au nanocrystals firstly. Based on the energy-band theory, a mechanism of the efficient separation of electron-hole pairs has been proposed to illustrate the improved photoelectric and photocatalytic properties of the Cu2SnSe3-Au heteronanostructures as compared to the bare Cu2SnSe3. In addition, the synthetic strategy of the Cu2SnSe3-Au heteronanostructures may open a route for the synthesis of the other semiconductor-metal heteronanostructures.4. The Cu2SnTe3 nanocrystals with cubic phase have been synthesized for the first time via a solution phase method. High-quality, uniform shape and size, monodisperse Cu2SnTe3 nanocrystals have been prepared by a colloidal hot-solution injection method using tellurium dioxide, copper acetylacetonate and tetraphenyltin as precursors in oleylamine and 1-dodecanethiol. Importantly, such synthetic strategy without using the expensive, hazardous and air-sensitive alkylphosphines (such as trioctylphosphine or tributylphosphine) may open a new route for controllable synthesis of other metal telluride nanostructures. In addition, the ternary Cu2SnTe3 nanocrystals demonstrate strong absorption in vis-NIR regions and possess an optical band gap of 1.18 eV. Optoelectronic measurements suggest that the photodetector based on the Cu2SnTe3 nanocrystals exhibits excellent performance and stability.