Graphene oxide (GO) has great potential in organic optoelectronic devices as a hole injection material. However, it is difficult to achieve high quantum efficiency for organic light-emitting didoes(OLED) using GO alone because there is a big energy level mismatch and large roughness between GO and light emission layer. In this work, a composite hole transport material combining GO with water soluble copper phthalocyanine (TSCuPc) was adopted to achieve energy level matching between ITO anodes and emission layers, and further to realize both high hole injection efficiency and high hole transport efficiency. It is shown in our results that the effective HOMO energy level of GO varies with its atomic layer thickness, therefore good energy level matching between GO with ITO anodes and low energy barrier for holes injection can be achieved by adjusting GO layer thickness. Combining TSCuPc having appropriate thickness with GO can significantly reduce the roughness of hole injection interface and improve the directional migration rate of holes from the anode to the emitting layer, which thereby enabled the devices to achieve higher injection currents at the same operating voltage. Compared with the devices using GO alone or TSCuPc alone as the hole transport layer, the OLEDs with the composite hole layer of GO and TSCuPc obtained a higher current-luminance conversion efficiency and 2.2Voflow turn-on voltage, which indicates that the composite hole transport layer of GO and TSCuPc is effective to improve the quantum efficiency of OLEDs. The property of adjustable HOMO level of GO and the property of strong charge coupling between GO and organic molecules are beneficial to construct high efficient composite hole transport materials.
A novel sensor for detecting particulate matter 2.5 (PM2.5, particles with a diameter smaller than 2.5 μm) concentration in environment air is presented by using modal interference in a photonic crystal fiber (PCF). The sensor is composed of a single mode-multimode-PCF-multimode-single mode optical fiber, and the corresponding polypyrrole (PPy) sensing nanofilm with a light-inducing characteristic is synthesized onto the outside surface of a PCF in-situ by an interfacial ploymerization method. The experimental result shows that the thickness of the sensing film is within the range of 100~150 nm by a scanning electron microscope. When the sensor is placed in PM2.5 air flow, the PM2.5 particles are absorbed onto the surface of a PPy sensing film due to a light-inducing electrostatic effect, resulting in the refractive index (RI) change of a sensing film. For PM2.5 air flow with a concentration of 55 μg/m3 and a sampling time of 30 min, the characteristic wavelength of the interference spectra has a blue shift with 1 nm. After turning off the light source, the characteristic wavelength of the sensor is back to the initial value owing to no light-inducing electrostatic effect and the PM2.5 particles desorbing. The sensor has a good reversibility.
A photonic crystal fiber sensor was prepared for refractive index sensing. Based on modal interferometer theory, the
relationships between the refractive index of glycerine solution and resonant wavelength shift of the sensor are
analyzed by numerical simulation. A fiber optical device was designed to operate the sensing experiment. The
sensing experiment shows that the resonant wavelength blued-shift for the sensor with refractive index in the range of
1.33~1.41 happens when increasing glycerine solution from 0.0% to 50.0% (v/v). The experimental results are
approximately consistent with theory.
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