Hwan-Sool Oh

Role of CsF on electron injection into a conjugated polymer

We studied electron injection from Al and Au cathodes into the conjugated polymer poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH–PPV). When a thin CsF layer is inserted between MEH–PPV and Al, a substantial enhancement in electron injection is observed. Insertion of the same layer between MEH–PPV and Au does not have a similar effect, indicating that the enhancement mechanism is specific to CsF and Al. Thin Cs layers enhance electron injection regardless of the cathode metal. A mechanism that explains these observations is proposed.

5 V Input Level Shifter Circuit for IGZO Thin-Film Transistors

A 5V input level shifter circuit based on depletion-mode In-Ga-Zn-O thin-film transistors (TFT) worked up to 100 kHz. By employing metal-insulator-semiconductor (MIS) active capacitor, we enhanced the bootstrapping effect and reduced the rise time of the output signal. SPICE simulation results showed that the proposed level shifter worked for wide threshold voltage range from !2V to D1V and the fabricated circuit exhibited the propagation delay tplh and tphl of 0.6 μsec and 0.3 μsec respectively.

Fabrication of a White Organic Light Emitting Diode By Synthesizing a Novel Non-conjugated Blue Emitting Material PPPMA-co-DTPM Copolymer

To fabricate a single layer white organic light emitting diode (OLED), a novel non-conjugated blue emitting material PPPMA-co-DTPM copolymer was synthesized containing a perylene moiety unit with hole transporting and blue emitting ability and a triazine moiety unit with electron transporting ability. The devices were fabricated using PPPMA-co-DTPM copolymer by varying the doping concentrations of each red, green and blue fluorescent dye, by molecular-dispersing into Toluene solvent with spin coating method. In case of ITO/PPPMA-co-DTPM:TPB structure, as they were molecular-dispersing into 30 mg/ml Toluene solvent, nearly-pure white light was obtained both (0.325, 0.339) in the CIE coordinates at 18 V and (0.335, 0.345) at 15 V. The turn-on voltage was 3 V, the light-emitting turn-on voltage was 4 V, and the maximum external quantum efficiency was at 24.5 V. Also, in case of using 40 mg/ml Toluene solvent, the CIE coordinate was (0.345, 0.342) at 20 V.

A shift register for depletion-mode oxide TFTs with very low power consumption

The shift register comprised of metal-oxide thin-film transistors (TFTs) is apt to exhibit anomalously high power consumption because the oxide TFT often has depletion-mode characteristic. We have developed a new shift register circuit in which one of the pull-down TFTs is controlled by capacitive coupling with the clock signal and the input carry signal. Employing this structure, the TFTs with non-zero VDS are always turned off with negative VGS. As a result, unnecessary current through the TFTs is eliminated and the power consumption of the new circuit decreases to the half of our previous one when the threshold voltage of the TFT is 5V.

Analysis of the Characteristics of a White OLED using the Newly Synthesized Blue Emitting Material nitro-DPVT by Varying the Doping Concentrations of Fluorescent Dye and the Thickness of the NPB Layer

A stacked white organic light-emitting diode (OLED) having a blue/orange emitting layer was fabricated by synthesizing nitro-DPVT, a new derivative of the blue-emitting material DPVBi on the market. The white-emission of the two-wavelength type was successfully obtained by using both nitro-DPVT for blue~emitting material, orange emission as a host material and Rubrene for orange emission as a guest material. The basic structure of the fabricated white OLED is glass/ITO/NPB/nitro-DPVT/nitro-DPVT:. To evaluate the. characteristics of the devices, firstly, we varied the doping concentrations of fluorescent dye Rubrene from 0.5 % to 0.8 % to 1.3 % to 1.5 % to 3.0 % by weight. A nearly pure white-emission was obtained in CIE coordinates of (0.3259, 0.3395) when the doping concentration of Rubrene was 1.3 % at an applied voltage of 18 V. Secondly, we varied the thickness of the NPB layer from by fixing doping with of Rubrene at 1.3 %. A nearly pure white-emission was also obtained in CIE coordinates of (0.3304, 0.3473) when the NPB layer was thick at an applied voltage of 16 V. The two devices started to operate at 4 V and to emit light at 4.5 V. The external quantum efficiency was above 0.4 % when almost all of the current was injected.

A Study on the Characteristic Analysis of ITO and the Fabrication of Organic Light Emitting Diodes by Variation of Plasma Condition

In this experiment, OLEDs(Organic Light Emitting Diodes) was fabricated to confirm effect of Plasma treatment which increase the hole injection characteristic from anode. Device structure was . We used DPVBi (4, 4 - Bis (2,2-diphenylethen-1-yls) - Biphenyl) as a blue emitting material. To optimize the process condition of plasma treatment, we used 2 gases of the oxygen and nitrogen gas under 120 mTorr with 100 W, 200 W, and 400 W plasma power. The current efficiency of plasma is more efficient than that of plasma. At , we obtained the maximum current efficiency of 6.45 cd/A using gas with 200 W plasma power.

A Study on the fabrication and Characteristic Analysis of Organic Light Emitting Device using Inorganic Metal Multi-layer

IMML(Inorganic metal multi-layer) was used as cathode in the OLED devices to reduce the reflectance or ITO and increase the contrast ratio. Device structure was . and DCJTB (4 - (dicyanomethylene) - 2 - ( 1 - propyls) 6 - methy 4H - pyrans) as host material lot red emission and red emitting guest material. IMML made three different layer: thin aluminum layer, aluminum layer doped with silicon monoxide, thick aluminum layer. The red OLED device with IMML showed the average reflectance of , and then normal OLED with or without polarizer showed the average reflectance of , at visible range from 380 nm to 780 nm. The brightness of OLED with IMML at 13 V was 5557 , and that of normal OLED with polarizer was 4872 . IMML could be the substitution for polarizer with same reflection, low cost, easy process in flat panel display market.