Yong Kyun Lee

Resonant tunneling diode made of organic semiconductor superlattice

The authors studied the current-voltage characteristics of the organic superlattices of an ITO/1,3,5-tris-(3-methylphenylphenylamino) triphenylamine (m-MTDATA) (5nm)∕[m-MTDATAand4,7diphenyl-1,10-phenanthroline(Bphen)]4∕Bphen (5nm)∕LiF∕Al. The thickness of m-MTDATA was varied from 3to7nm with the fixed Bphen thickness at 3nm. The current-voltage characteristics of the organic superlattice show a peak and a valley between 3 and 8V when the thickness of m-MTDATA is 7nm, which is due to the resonant tunneling currents. It is found that there is no luminance by the resonant tunneling currents.

Synthesis of new PPV based polymer and its application to display

Abstract We have synthesized PPV derivative containing an adamantane side group, poly(1-(2-ethylhexyloxy)-4-(1-adamantaneethyloxy)-2,5-phenylenevinylene, EHAE-PPV) and fabricated the segment device using this polymeric electroluminescent material. EHAE-PPV is solution processable and shows high photoluminescence intensity, probably due to the steric effect of the adamantyl group. This polymer also has exhibited good electroluminescent properties.

High-Efficiency White Polymer Light-Emitting Diodes Based on Blended RGB Polymers

We have fabricated white polymer light-emitting devices (WPLEDs) from RGB polymer blending systems using ITO/PEDOT:PSS/blended polymers/LiF/Al structure. The highest current efficiency reached 5.34 cd/A and the maximum brightness value of 27,000 cd/m2 at 11.4 V was obtained. As the green dopant concentration increased, the spectrum deviated from the white because of more energy transfer from host to guest. As a result, the 450 nm blue peak was reduced by increasing green dopant ratio. On the other hand, 600 nm red shoulder peaks were slightly increased at the same conditions. Therefore, red-orange and green electroluminescence emissions are promoted by excitation energy and charge transfer from the blue host polymer to the dopants.

Improvement of Current Injection and Efficiency of Polymer Light-Emitting Diodes with the Octadecyltrichlorosilane-Treated PEDOT:PSS

We studied the improvement of a polymer light-emitting diode (PLED) by inserting an interlayer between a poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and an emissive layer. An octadecyltrichlorosilane (OTS) was treated on the PEDOT:PSS as the interlayer. It improved the device efficiency of the PLED from 4.4 to 5.3 cd/A, and increased the maximum luminance from 10,000 to 17,000 cd/m 2 . It increased the forward current by 20% and reduced the reverse current by 80%. Inserting the OTS layer between PEDOT:PSS and the emissive polymer reduced the injection barrier between the PEDOT:PSS and emissive layer. Therefore, the increases of the effective work function of the anode led to better hole injection and thus, higher current density.

Spontaneous Patterning of Polymer Film by Teflon Thin Film and Spin Coating for Polymer Light-Emitting Diode

We have developed a selective coating technology for large-area polymer light-emitting devices (PLEDs). This can be done by using the different surface energy on the anode electrode. Teflon thin film can be used to make a hydrophobic surface (low surface energy) on the hydrophilic surface (high surface energy) of ITO for patterning of polymer film. Contact angle of ITO surface and Teflon coated one were 3 and 130°, respectively. In order to demonstrate PLED by spontaneous patterning of polymer film we have fabricated PLED consist of 4 and 8 elements in series on the same substrate. The voltage of the devices required to achieve a particular brightness scales approximately with the number of elements in series.

Self-Assembled Monolayer Modification of PEDOT:PSS Interface to Improve the Device Performance in Blue PLED

As a result of intensive research on polymer light-emitting diodes (PLEDs) for the last several years, the device performances have been remarkably improved. Recently, several researchers reported on a PLEDs with an interlayer between poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and an emissive polymer. It improved the device efficiency as well as the device lifetime. The role of the interlayer is to block the electron from back diffusion to PEDOT:PSS and/or to reduce luminescence quenching at the PEDOT:PSS interface. We studied the improvement of the PLED by inserting an octadecyltrichlorosilane (OTS) as the interlayer between PEDOT:PSS and the emissive layer. The OTS was treated on PEDOT:PSS through the self-assembled monolayer (SAM) process. It improved the device efficiency of the PLED from 3.86 to 4.76 cd/A, and increased the operation lifetime from 270 to 340 minute comparing the non-OTS treated PLED with the OTS treated PLED for 10 min. In blue PLED, inserting the OTS layer between blue polymer and PEDOT:PSS is promoted hole injection from an anode. Therefore, the device efficiency is improved, which appears to be due to the increase of balanced recombination as a result of the accumulated electrons near the interface between emissive layer and PEDOT:PSS.

Color Variation Improvement by Introducing Double Emission Layers in WPLEDs

We have fabricated white polymeric light-emitting devices (WPLEDs) from polyfluorene-based (PFO) blue and MEH-PPV polymer blending systems. A device structure of ITO/PEDOT:PSS/Blending polymer/Blue polymer/LiF/Al was employed. This double emissive structure results in the significant improvement of white color shift phenomenon. A current efficiency of 4.67 cd/A (3,900 cd/m2, 6.4 V) and a brightness value of 17,600 cd/m2 at 9.4 V with (0.34, 0.35) CIE coordinates at 5 V and (0.29, 0.29) at 9 V were obtained.

49.2: 2 Inch AMOLED with a-Si:H TFT using PVP Gate Insulator on Plastic Substrate

We developed an 80 DPI, bottom emission AMOLED (2 inch) on transparent plastic (PES). Hydrogenated amorphous silicon (a-Si:H) on plastic using a PVP (Poly-4-vinylphenol) gate insulator was used for switching and driving TFTs. The low temperature process (<150 °C) and the island formation of inorganic layers give a stress-free AMOLED backplane on PES. The a-Si:H TFT has a field-effect mobility of 0.5 cm2/Vs, a threshold voltage of 4.7 V and subthreshold slope 1.0 V/dec.

P‐184: A High Efficiency Bilayered Red Phosphorescent OLED

We report a high efficiency red phosphorescent OLED (PHOLED) with organic bilayered structure. The structure of bilayered red PHOLEDs was ITO/ N,N″-di(naphthalene-1-yl)-N,N″-diphenyl-benzidine (NPB)/new host: Ir(piq)3/LiF/Al. A high current efficiency of 10.0 cd/A and a power efficiency of 7.8 lm/W at 500cd/m2 was demonstrated in this device. The operation driving voltage to reach 1000 cd/m2 was 4.5 V and CIE coordinate was (0.67, 033). This bilayered PHOLED fabricated by a new phosphorescent host material resulted about 3 times enhancement of power efficiency compared with that of a CBP based control device.

34.1: A 2.2-in. Top-Emission AMOLED on Flexible Metal Foil with SOG Planarization

We have developed a 2.2 inch top-emission AMOLED display on flexible metal foil with an inverted staggered TFT using P-SOG (phosphosilicate-based spin-on-glass) as a gate insulator. The gate insulator was planarized on flexible metal foil by spin coating. The p-channel poly-Si TFT on metal foil exhibited the field-effect mobility of 51.2 cm2/Vs, threshold voltage of −5.3V, and the gate voltage swing of 1.0 V/dec. Green AMOLED with 128×160 pixels was demonstrated with a LTPS AM backplane with 2 TFTs and 1 capacitor in a pixel.