Mu-gyeom Kim

Hole-injecting conducting-polymer compositions for highly efficient and stable organic light-emitting diodes

This letter introduces conducting polymer compositions which can be used for hole-injection layer in organic light-emitting diodes. The compositions are composed of poly (3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonic acid (PSS) and a perfluorinated ionomer. The films based on these compositions showed much higher workfunction (∼5.3–5.7eV) than conventional PEDOT/PSS (∼5.0–5.2eV). When we fabricated blue polymer light-emitting diodes by using these compositions as a hole-injection layer, the luminescent efficiency was improved and the device lifetime was also enhanced relative to the device using the commercially available PEDOT/PSS. These compositions including perfluorinated ionomers can be one of the promising candidates for a hole-injection layer in organic light-emitting devices.

Hole-transporting interlayers for improving the device lifetime in the polymer light-emitting diodes

The authors report the effect of thermal treatment of hole-transporting interlayers between a polymeric hole injection layer and an emitting layer (EML) on the luminous efficiency and the lifetime performance in blue polymer light-emitting diodes. As the thermal annealing temperature of the interlayer increased, the hole mobility of the interlayer tended to decrease, which results in reducing the hole current injected into the EML in the devices. Hence, the device luminous efficiency decreased due to lower electron-hole balance. Nevertheless, the device lifetime increased, which can be attributed to the formation of the thicker interlayer and the better defined interlayer/EML interface.

Electron injection enhancement by a Cs-salt interlayer in ambipolar organic field-effect transistors and complementary circuits

Here we report the effects of a Cs-salt based charge injection interlayer on the characteristics of top-gate/bottom-contact (TG/BC) ambipolar polymer OFETs with poly(thienylenevinylene-co-phthalimide)s functionalized at the imide nitrogen with dodecyl (PTVPhI-C12). P-channel dominant PTVPhI-C12 ambipolar OFETs showed both an improved electron injection and blocked hole injection properties by insertion of a thermally deposited thin CsF interlayer between Au source/drain electrodes and the organic semiconductor. X-ray and UV photoelectron spectroscopy results exhibited that the work-function of the Au electrode progressively changed from −4.5 eV to −3.9 eV and the Fermi levels of PTVPhI-C12 concomitantly moved towards the LUMO level of the conjugated polymer with an increase of CsF thickness from 0 nm to 1.5 nm, respectively. Both the shifting of Au work-function and the molecular doping of PTVPhI-C12 by insertion of CsF provide an order of magnitude improved n-channel properties in p-channel dominant ambipolar PTVPhI-C12 OFETs. In the end, the characteristics of the PTVPhI-C12 complementary inverter were improved (gain > 23) by a selective deposition and optimization of the CsF interlayer thickness on the n-channel region of ambipolar CMOS inverters.

A Study of Parasitic Series Resistance Components in In–Ga–Zn–Oxide (a-IGZO) Thin-Film Transistors

We extracted the effective channel length and parasitic series resistance in a-IGZO inverted-staggered etch-stop (ES) TFTs. When there is an overlap between the drain or source electrode and the FET channel, the resistance of the channel underneath the overlapping regions is very low compared with other channel region resistance. As a result, the effective channel length is smaller than the physical length. The aforementioned definition of effective channel length in terms of device geometric parameters seems to be specific for ES a-IGZO TFTs.

A 3.0-in. 308-ppi WVGA AMOLED with a top-emission white OLED and color filter

— A 3.0-in. 308-ppi WVGA top-emission AMOLED display with a white OLED and color filters, driven by LTPS TFTs demonstrating a color gamut of >90% and a Δ(u′,v′) of <0.02 is reported. A white-emission source with a unique device structure was developed using all fluorescent materials and yielded efficiencies of 8.45% and 16 cd/A at 4000 nits with CIE color coordinates of (0.30, 0.32).

54.4: Highly Efficient and Wide Color Gamut White OLED Architecture for Display Application

Highly efficient WOLEDs, with the efficiencies of 19 cd/A, 16 cd/A, and 33 cd/A and CIE color coordinates of (0.25, 0.35), (0.30, 0.32), and (0.30, 0.32) respectively, have been developed. The broad white emitting TE-WOLEDs for high resolution display have been realized by controlling the microcavity between the cathode and anode. 96 % of NTSCx,y ratio was achieved from the TE-WOLED with the optical path control layer (OPCL) and new green color filter (CF).

P-228: Degradation of White Light Emitting OLEDs

We firstly report the degradation analysis of multilayer structured WOLED by using spectroscopic and microscopic analytical methods. Our analytical results demonstrated that the interface between cathode and electron-transporting layer is responsible for the intrinsic long-term degradation of WOLEDs.

Electric Field–Induced Ordering of the Worm-Like Micelles: Application to the Low-Dielectric-Constant Materials

We propose a new method to form solid, silicon-containing, substrate-supported films with ordered cylindrical pores. Such films may be used as low-dielectric-constant interlayers in microelectronics. First, liquid films are obtained in a plane-parallel glass capillary, using a precursor solution of the worm-like micelles as a template. An ac electric field of the order of 104 V/cm is applied to orient the micelles in one direction. Further on, after solidification of the precursor solution under the field and its calcination in a vacuum furnace, solid dielectric films are formed. These films possess high mechanical modulus and are expected to have low dielectric constants.

Failure Mode Investigation for Blue Polymer EL Device

We report the failure mode observed in polymer EL blue device. Such modes were analyzed by non-destructive and destructive ways. As a non-destructive way, investigation of mobility changes of hole and electron, measuring transient EL corresponding to life curve, had been done. We also observed compositional and morphological variation using TEM-EDX, STM, FT-IR, TOF-SIMS and reverse engineering method as a destructive way. Electron mobility has a higher dependency on life curve, which fact could be reflected on the formation of insoluble layer inside emitting layer on anode side. And such insoluble layer showed relatively ordered surface morphology, and might be a cross-linked layer through C-O-C bond cleavage process while EL operation. But, contrary to sulfur migration mechanism into insoluble layer insisted by CDT, we did confirm no obvious difference of sulfur composition between insoluble and emitting layers. Rather, theres some degree of Ba diffusion into emitting layer from decomposition of BaF 2 , but, which dose not have a major effect on device degradation.