Dong Joon Choo

Lifetime of organic thin-film transistors with organic passivation layers

We fabricated a high-performance pentacene organic thin-film transistor (OTFT) on plastic and passivated it with polyvinylalcohol and photosensitive acryl layers. The pentacene was grown on the thin-film transistor area using a self-organized process. The OTFT after the passivation exhibited the field-effect mobility of 0.80cm2∕Vs, threshold voltage of −9.2V, and on/off current ratio of 108. The field-effect mobility and threshold voltage change exponentially with time in air. The lifetime, defined as the time required to decrease the on current by one-half, was found to be ∼11000h in ambient air. The absolute value of threshold voltage of the unpassivated OTFT increases with time in air, but it decreases with time in the passivated OTFT. This indicates that the origins for the degradation in the performances of the two OTFTs are different. H2O in unpassivated and O2 in passivated OTFT appear to be the major origin for the degradation.

High performance organic thin-film transistors with photopatterned gate dielectric

The authors have fabricated high performance pentacene organic thin-film transistor (OTFT) using photopatternable poly(4-vinylphenol) gate dielectric on plastic substrate. The dielectric layer was composed of poly(vinylphenol), 1,2,4,5-tetraacetoxymethylbenzene, and 2,4-bis(trichloro methyl)-6-aryl-1,3,5-triazine. The 1,2,4,5-tetraacetoxymethylbenzene is a cross-linking material which is synthesized by a two-step reaction. The gate dielectric was patterned by spin coating and UV exposure. The OTFT with photopatterned gate dielectric exhibited a field-effect mobility of 1.23cm2∕Vs and a threshold voltage of −6.5V and an on/off current ratio of 107, so that the OTFT can be applied to make a high performance display.

Synthesis and characterization of the first adamantane-based poly(p-phenylenevinylene) derivative: an intelligent plastic for smart electronic displays

Abstract A novel poly( p -phenylenevinylene) (PPV) derivative containing adamantane substituent—poly(2-methoxy-5-adamantaneethyloxy- p -phenylenevinylene) (MAE-PPV) is synthesized through the Gilch route. Adamantane was incorporated into this polymer because of its rigid and spherical structure, which results in reduction of interchain interaction. MAE-PPV is solution processable and shows high photoluminescence intensity. This polymer also demonstrates good electroluminescene properties.

Examination of EL and PL properties of MCHM-PPV and MEH-PPV: a study towards introduction of a new series of thin film EL devices

Abstract The effect of the side group, employed during synthesis, on the PL (photoluminescence), EL (electroluminescence) profiles and the light intensity of PPV derivatives has been investigated using MEH (methoxy-ethyl-hexyloxy) and MCHM (methoxy-cyclo-hexyl-methyloxy) as side groups. The measurements show that even the most subtle change in molecular structure of PPV has a marked improvement on the EL, PL profiles and the light emission intensity. It has been found that the PL and EL intensities of the MCHM-PPV are higher than those of MEH-PPV. MCHM-PPV also demonstrated higher light emission at lower potentials and currents.

Solvent Effect of the Passivation Layer on Performance of an Organic Thin-Film Transistor

We studied the passivation of pentacene organic thin-film transistors (OTFTs) on plastic using four kinds of organic layers: photopatternable acryl (PA), polyvinylalcohol (PVA)/dichromated polyvinylalcohol (D-PVA), PVA/D-PVA/PA, and parylene-C. The initial mobility of the OTFTs was ∼ 1.0 cm 2 /V s and the on/off current ratio was ∼10 7 . The drop in the on-current and the increase in the off-currents were significant when PA was used as a passivation layer because of the damage to the pentacene active layer by the organic solvent in PA solution. On the other hand, there was little change in the performance of the OTFT when PVA/D-PVA was used as the passivation layers on the pentacene. This was done to reduce the concentration of metal ionic impurity at the interface of the pentacene and PVA. The OTFT with the passivation layers exhibited a field-effect mobility of 0.8 cm 2 /V s and on/off current ratio of 10 7 . This means that the water soluble PVA can minimize the damage to the pentacene and prevent the penetration of the organic solvent in PA solution.

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.

63.3: High Resolution OTFT-OLED on Plastic Substrate Using Self-organized Process

A high resolution (2 inch, 80 dpi) organic thin-film transistor driven light-emitting diode has been developed on plastic substrate. The pentacene OTFT array was fabricated using self-organized process. The TFT in the array exhibited an average field-effect mobility of ∼1 cm2/Vs, an on/off current ratio of 107, and a threshold voltage of ∼ −8 V after the bank formation with parylene-C / SiNx, which is good enough to drive OLEDs. An AMOLED was driven in the bent state of 100 mm radius.

The effect of transition metals coated by the laser ablation technique on the photoluminescence of MEH-PPV(poly(2-methoxy,5-(2′-ethyl-hexyloxy)-p-phenylenevinylene))

Abstract Using transition metals including Ni, Fe and Cu as dopants and MEH-PPV (poly(2-methoxy,5-(2′-ethyl-hexyloxy)- p -phenylenevinylene)) as the organic material we studied the PL intensity of the doped polymer. It has been found that PL intensities decreased by laser ablation of metals in all cases except in the case of Fe when the laser ablation process was carried out for 30 s.

31.4: Solvent Effect on Uniformity of the Performance of Inkjet Printed Organic Thin-Film Transistors for Flexible Display

We have studied solvent effect on the uniformity of the performance of the organic thin film transistors (OTFTs) by inkjet printing using TIPS pentacene as an active layer. A 1,2,4-trichlorobenzene and cyclohexanol were used to control the viscosity for TIPS pentacene printing process. The uniformity of the performance of the TIPS pentacene TFT was greatly improved.