Investigation On High Performance Solution-Processed Organic Light-Emitting Diodes (OLEDs)

Organic light emitting devices have been extensively studied due to their desired properties, such as low thickness, light weight, low fabrication cost, low power loss,better vision, fully solid state, self-luminous, low driving voltage and compatible with flexible substrates etc. Current research work mainly focused on the development of new luminescent materials and new carrier transport materials, exploring new device manufacturing technology and device structure, studying the luminescence mechanism,to improve the carrier injection, reduce the driving voltage, improve the radiative recombination rate of electrons and holes in the light-emitting layer, and reduce the loss of light and so on.In order to improve the performance of a single material based interfacial laye,effective hybrid charge injection layer is generally prepared by doping organic and inorganic materials. The generation of charge transfer in doped organic-inorganic hybrid materials would result in obviously improved carrier injection in OLEDs. We develop an aqueous solution-processed hole injection layer, inorganic salt Mo O3 doped organic salt copper phthalocyanine-3,4’,4’’,4’’’-tetra-sulfonated acid tetra sodium salt(TS-CuPc), in organic light-emitting diodes(OLEDs) via an environmentally-friendly and easy fabrication process. The generation of charge transfer complex in TS-CuPc:Mo O3 composite films is confirmed by absorption spectra and X-ray photoemission spectroscopy(XPS) measurements, which makes it possible for fabricating near-infrared photoelectric devices.. In terms of the performance, devices based on organic-inorganic hybrid charge injection layer not only have a lower driving voltage, but also a higher efficiency compared with the single material as the chargeinjection layer. Through the temperature-dependent current-density voltage(J-V)characteristics evaluation, the enhanced hole injection in OLEDs is attributed to the decreased hole barrier at the ITO side, which is in agreement with the Schottky thermal emission mechanism. The efficient modification of ITO by TS-CuPc:Mo O3 is further confirmed by ultraviolet photoemission spectroscopy(UPS) measurements.A new red phosphorescent material Ir(dmppm)2(dmd), which is a pyrimidine-based iridium(III) complex, has been synthesized and successfully used to fabricate solution-processed red and white organic light-emitting diodes(OLEDs). Due to its excellent solubility in common organic solvents and its good compatibility with the host material, a record current efficiency of 27.2 cd A-1 so far has been achieved for partially solution-processed red OLEDs by using Ir(dmppm)2(dmd) as a dopant. Furthermore, the fabricated two-component ‘‘warm-white’’ OLEDs based on the Ir(dmppm)2(dmd) red emitter demonstrate a maximum current efficiency of 28.9 cd A-1, which can meet the call for physiologically-friendly indoor illumination to some extent. Based on the synthesis of new red phosphor material, with the advantages of high quantum efficiency,easy fabrication process, low fabrication cost, this promising phosphorescent dopant could be widely used in the fabrication of solution-processed OLEDs.