Ma Dongge

High Current Transfer Ratio Organic Optocoupler Based on Tandem Organic Light-Emitting Diode as the Input Unit

An organic optocoupler (OOC) is fabricated with a tandem organic light-emitting diode (OLED) as the light source (input unit) and an organic photodiode (OPD) as the detector (output unit). It is found that using the tandem OLED as the input unit can significantly increase the current transfer ratio of the organic optocoupler. When the tandem OLED operates under 8 V and the OPD operates under −4 V, the current transfer ratio of the optocoupler reaches 5.4%. Simultaneously, the ION/IOFF ratio of the optocoupler reaches 105, which can be attributed to the small leakage current of the OPD, and the high efficiency of the OPD and the tandem OLED.

Nonvolatile Memory Effect in Organic Thin-Film Transistor Based on Aluminum Nanoparticle Floating Gate

A nonvolatile memory effect was observed in an organic thin-film transistor by introducing a Boating gate structure. The Boating gate was composed of an Al film in a thickness of nanometers, which was thermally deposited on a SiO2 insulator and exposed to air to spontaneously oxidize. It can be seen that the transistors exhibit significant hysteresis behaviors and storage circles in current-voltage characteristics in the dark and under illumination, indicating that the transistors may act as a nonvolatile memory element. The operational mechanism is discussed in the cases of dark and illumination via charge trapping by the Al floating gate.

Improved Performance by a Double-Insulator Layer in Organic Thin-Film Transistors

Organic thin film transistors based on pentacene are fabricated by the method of full evaporation. The thickness of insulator film can be controlled accurately, which influences the device operation voltage markedly. Compared to the devices with a single-insulator layer, the electric performance of devices by using a double-insulator as the gate dielectric has good improvement. It is found that the gate leakage current can be reduced over one order of magnitude, and the on-state current can be enhanced over one order of magnitude. The devices with double-insulator layer exhibit field-effect mobility as large as 0.14 cm(2)/Vs and near the zero threshold voltage. The results demonstrate that using proper double insulator as the gate dielectrics is an effective method to fabricate OTFTs with high electrical performance.

Nonvolatile Memory Devices Based on Gold Nanoparticle and Poly (N-Vinylcarbazole) Composite

A rewritable polymer memory device based on gold nanoparticle doped poly (N-vinylcarbazole) (PVK), which can be easily fabricated by simple spin coating, has been described. An electrical bistable phenomenon is observed in the current-voltage characteristics of this device, and it is found that the electrical bistability is repeatable by proper writing voltage and erasing voltage. The unique behaviour of the devices provides an interesting approach such that doping nanoparticles in polymer can be used to realize high performance nonvolatile polymer memory devices.

Low-Threshold Conjugated Polymer Distributed Feedback Lasers on InP Substrate

We demonstrate a low threshold polymer solid state thin-film distributed feedback (DFB) laser on an InP substrate with the DFB structure. The used gain medium is conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) doped polystyrene (PS) and formed by drop-coating method. The second order Bragg scattering region on the InP substrate gave rise to strong feedback, thus a lasing emission at 638.9 nm with a line width of 1.2 nm is realized when pumped by a 532nm frequency-doubled Nd:YAG pulsed laser. The devices show a laser threshold as low as 7 nJ/pulse.

Performance Improvement of Organic Thin Film Transistors Based on Gate Insulator Polymethyl-Methacrylate-co-Glyciclyl-Methacrylate

Organic thin transistors (OTFTs) on indium tin oxide glass substrates are prepared with polymethyl-methacrylate-co-glyciclyl-methacrylate (PMMA-GMA) as the gate insulator layer and copper phthalocyanine as the organic semiconductor layer. By controlling the thickness, the average roughness of surface is reduced and the OTFT performance is improved with leak current decreasing to 10−11 A and on/off ratio of 104. Under the condition of drain-source voltage −20 V, a threshold voltage of −3.5 V is obtained. The experimental results show that PMMA-GMA is a promising insulator material with a dielectric constant in a range of 3.9–5.0.

Synthesis and properties of pyridine-containing bipolar host materials for blue phosphorescent OLEDs

Pyridine derivatives are usually used as electron transport moiety in bipolar host materials or electron transport materials due to their good electron transport ability and high triplet energy. Two new pyridine-containing bipolar materials, named DTPAPPy and DCzPPy, were designed and synthesized by incorporating electron-donating triphenylamine or carbazole and electron-accepting pyridine into one molecular. They showed relatively high triplet energy of 2.64 eV for DTPAPPy and 2.70 eV for DCzPPy, respectively. The blue phosphorescent OLEDs hosted by DTPAPPy and DCzPPy achieved maximum current efficiencies of 15.4 and 25.3 cd/A, respectively.

Fabrication of an integrated pixel with an organic light-emitting diode driven by copper phthalocyanine organic thin film transistors

An organic integrated pixel with organic light-emitting diodes (OLEDs) driven by organic thin film transistors (OTFTs) is fabricated by a greatly simplified processing. The OTFTs are based on copper phthalocyanine as the active medium and fabricated on indium-tin-oxide (ITO) glass with top-gate structure, thus an organic integrated pixel is easily made by integrating OLED with OTFT. The OTFTs show field-effect mobility of 0.4 cm2/Vs and on/off ratio of 103 order. The OLED is driven well and emits the brightness as large as 2100 cd/m2 at a current density of 14.6 μA/cm2 at −19.7 V gate voltage. This simple device structure is promising in the future large-area flexible OLED displays.

Electrical Characteristics of Copper Phthalocyanine Thin-Film Transistors with Polyamide-6/Polytetrafluoroethylene Gate Insulator ∗

Polyamide-6(PA 6)/polytetrafluoroethylene is studied as a potential gate dielectric for flexible organic thin film transistors. The same method used for the formation of organic semiconductor and gate dielectric films greatly simplifies the fabrication process of devices. The fabricated transistors show good electrical characteristics. Ambipolar behaviour is observed even when the device is operated in air.

Electrical characterization of copper phthalocyanine thin-film transistors with fluoride gate insulator

Different fluoride materials are used as gate dielectrics to fabricate copper phthalocyanine (CuPc) thin film. transistors (OTFTs). The fabricated devices exhibit good electrical characteristics and the mobility is found to be dependent on the gate voltage from 10(-3) to 10(-1) cm(2) V(-1)s(-1). The observed noticeable electron injection at the drain electrode is of great significance in achieving ambipolar OTFTs. The same method for formation of organic semiconductors and gate dielectric films greatly simplifies the fabrication process. This provides a convenient way to produce high-performance OTFTs on a large scale and should be useful for integration in organic displays.