Synthesis, Characteristics and Applications of Novel Functionalized Graphene and Polystyrene-Silver Core-Shell Type Composites Based on Incorparation of Amino Groups

In this dissertation, the develop of the electrically conductive particles, composite films and the graphene-based electron acceptor are studied in different strategies. This research is divided into three parts, and discussed separately. In the first part, a solution-processed metal nanoparticle/graphene composite material is developed by the incorporation of functionalized reduced graphene oxide (RGO) nanosheets, which are synthesized via diaozotization process in the presence of –SH, –SO3Na or –NH2 functional groups. In the beginning, the RGO is prepared by the oxidation of natural graphite powder and the thermal reduction of graphene oxide (GO). Both of the functionalized RGO nanosheets (RGO-SO3 and RGO-NH2) show the improved dispersibility in aqueous phase with two different functional groups –SO3Na and –NH2, respectively. After a simple in-situ reduction method, Ag nanoparticls can be distributed uniformly on the surface of functionalized RGO and utilized as conductive spacers between the graphene nanosheets. The best electrical conductivity of around 2080 S/cm at a transmittance of 88 % (at λ=550 nm) is obtained with the well-dispersed Ag@RGO-SO3 in the PEDOT:PSS matrix. By making good use of the conducting network built up by the graphene, conductive spacers (Ag NPs) and conducting polymer, we demonstrate the promising application of these nanocomposite thin film as highly conductive and transparent electrodes for organic optoelectronic devices. Second, the ternary-blend organic photovoltaic device based on an acceptor of polyaniline-functionalized graphene (p-rGO) is demonstrated. The solution-processed graphene acceptor is first functionalized via diaozotization procedure, followed by the polyaniline chain covalently grafted on the surface of graphene. To further improve the charge transport at the interface of poly (3-hexylthiophene) (P3HT) donor and p-rGO acceptor, two novel thiophene-benzothiadiazole based small molecules, Tac and Taccn, end-capped with electron-withdrawing functional groups, carboxylic acid and 2-cyanoacrylic acid, respectively, is designed. The utilization of p-rGO as the electron acceptor material in P3HT bulk heterojunction photovoltaic (BHJ) devices is first demonstrated. Afterwards, the device of ternary blend BHJ organic solar cells using Tac as bridging materials shows an improved power conversion efficiency (PCE). Moreover, in Taccn series devices, the best performance is PCE of 2.03% and a short-circuit current density of 6.14 mA/cm2. The presented graphene-based acceptor shows the significance of developments in organic solar cells, and the ternary-blend BHJ is expected to be a practical approach for the fabrication of solar cell devices. In the last part, the core-shell type conductive particles based on the incorporation of polyaniline (PANI) as the activator are designed and fabricated to apply in electrically conductive adhesives. The polystyrene (PS) core particles with crosslinked structures are first prepared by dispersion polymerization to enhance the thermal stability, followed by the synthesis of PANI layer on the core surface via chemical oxidation polymerization. The modified electroless plating process is then utilized to fabricate the PS-PANI-Ag core-shell conductive particles. A series of reaction parameters, leading to various amounts of silver content and morphological effects, are investigated, including different ratios of aniline/PS and concentration of AgNO3. The prepared PS-PANI-Ag conductive particles have excellent electrical properties with Ag shells densely packed on the surface of PS-PANI cores. Moreover, the PS-PANI-Ag conductive particle are blended with environmentally friendly dispersions, water-borne polyurethane (WPU) to form electrically conductive films with a outstanding electrical property. The presented synthetic process exhibits a noteworthy relationship between the morphologies of core-shell particles and the electrical properties, and the environmentally friendly ECAs show the significant potential for the applications of electronic fields.