Controllable Syntheses And Properties Of Optoelectronic Nanomaterials For Solution-processed Devices

Optoelectronic devices, closely related to our daily life, can be widely used in many fields, such as computers, mobile phones, and home appliances. With the development of society, the conventional optoelectronic devices need to be updated and upgraded,because they cannot meet the demand of the society. At present, the solution-processed nanocrystal optoelectronic devices have many advantages, such as facile process, low cost, and consistent with low consumption of current social. In addition, the solution process can also prepare the large-area, flexible, and scalable photoelectric device to meet the need in unique fields, such as, electronic skins, smart windows, robot skins, and flexible displays. This thesis mainly focuses on the control syntheses and photoelectric properties of nanomaterials. Then, the nanomaterials were assembled into various optoelectronic devices by solution-based processes. The work summarized as follows,1) Transparent conducting oxide(TCO) nanocrystal(NC) ink assembled films. In recent years,the hot-injection method has become very popular for the synthesis of monodisperse TCO NCs, but the injection mode is difficult to scale-up, and very sensitive to the injection parameters. Herein, we report a facile, easily scale up, and universal one-pot method for the synthesis of a wide range of TCO NC, and the NC can be dispersed in various solvents serving as inks with stability for more than one year. When compared with the conventional hot-injection method for the synthesis of oxide NCs, a cheaper alcohol, namely DDL, instead of the expenxive 1,16-hexadecanediol, was used. The proposed approach is general for various TCOs as well as other oxide(e.g., CoO, MnO, Fe3O4, CdO) NC inks.The TCO NCs are highly crystalline, with a uniform morphology and a narrow size distribution, as well as an effective doping control and a high colloidal stability over one year, making them suitable as inks to print smooth, crack-free, highly transparent, and conductive films. The as-prepared ITO NC electrodes have a resistivity of 110 Ω/sq and a transparency of 88% under optimal treatment, and have a potential application in various solution process optoelectronics. Shaped ITO NCs were anisotropically grown into bipods(triangle), tripods, and tetrapods from spherical particle by adjusting the content of long-chain alcohol(1-dodecanol). Interestingly, such anisotropic ITO NCs exhibit shape-dependent localized surface plasmon resonances(LSPR). The resonance for the spherical ITO nanocrystal located at 1606 nm is highly symmetrical. A new peak located low energy band emerges and the peak intensity increases along with the increasingly anisotropic shape.Therefore, the synthesis of anisotropic shape nanocrystals and the plasmonic tunability can be used tounderstand interaction between shape and LSPR, which may broaden the application of TCO nanocrystals.2) Highly stable, conductive Cu@Cu-Ni nanowire elastomer composite electrodes. A scale-up one-pot method was developed to synthesize Cu NWs with Cu-Ni alloying shells via one-pot heating of CuCl2 and Ni(acac)2 in oleylamine. The nanowires with the highly crystalline alloyed shells, clear and abrupt interfaces, a length more than 50 μm, and smooth surfaces favor their stability and optical-electronic properties. We further demonstrate new conductive elastomer composites through embedding Cu@Cu-Ni NWs into polydimethylsiloxane(PDMS) to achieve high performances with transparency of 80% and resistance of 62.4 Ω/sq, which are even better than the typical PET/ITO(current commercial flexible electrodes). Meantime, the Cu@Cu-Ni nanowire elastomers have highly stability against oxidation, bending, stretching, and twisting. Significantly, the stable lifetime is estimated to exceed 1200 days in the natural environment and can meet the demand of industry. The Cu@Cu-Ni nanowire elastomer composites can well drive OLEDs under various bending(twisting and stretch). All nanowire and fully solution based PLEDs were prepared with structure of Cu nanowire/PEDOT: PSS/Polymer/PFN/Ag nanowire exhibiting highly flexibility. Because of high work function of Cu(4.7 eV), Cu nanowire is more suitable to be as anode than Ag nanowires(4.2eV).3) Solution process flexible Ag2 S nanocrystal resistive random access memory. Herein, we synthesized the high quality and monodisperse ~ 10 nm Ag2 S nanocrystals by a simple one-pot method. The as-obtained nanocrystals are of high crystallinity, uniform morphology, monodisperse size and colloidal stability for one year. Ag2 S nanocrystals can be dispersed in various solvent serving as inks. These merits lead inks ready to assemble into large area films via spin coating, drop coating,and liquid-liquid interface method. The flexible bipolar memory based Ag2 S nanocrystals/ploymer(polymetylmethacrylate, PMMA) organic/inorganic hybrid materials with low operating voltage(+1.03 V/-1.06 V), long retention time(>104 s), good endurance(>100 cycles), and excellent flexibility. Such process of Ag2 S nanocrystals/polymer organic/inorganic hybrid devices compatible with ink-jet printing, and roll-to-roll production, have a potential application in flexible electronics-based memory.4) Epitaxial ZnO nanowire-on-nanoplate structures as efficient and transferable field emitters.Here, we demonstrated a new strategy that utilizes hexagonal ZnO nanoplates as homogeneous nanoscale substrates for the epitaxial growth of ZnO nanowires, which results in very sharp and highly ordered interfaces and thus improves the FE performance. Owing to the free-standing nature of wire-on-plate(WOP) nanostructures, as well as their capability to self-assemble vertically, the productis demonstrated to be easily exfoliated and transferred onto other substrates, including flexible ones.After transferring the WOP dispersions by dip-coating, the turn-on field, threshold field, and field enhancement factor of the novel emitters could reach 4.8 V/μm, 8.1 V/μm, and 1004, respectively.These results suggest that the newly prepared ZnO nanostructures are highly promising as materials for transferable and flexible electronic devices.