Jieun Ghim

Effect of light irradiation on the characteristics of organic field-effect transistors

The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene (6-T) and pentacene was examined. Organic phototransistors (OPTs) in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage (Vth) or the switch-on voltage (VO), is the result of a slow release of accumulated ...

Effect of rubbed polyimide layer on the field-effect mobility in pentacene thin-film transistors

We investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number. In case of pentacene thin films deposited on rubbed PI at room temperature (RT), compared to unrubbed, the field-effect mobilities were improved by two- to threefold in contrast to the cases of elevated temperature. From the results of crystalline in-plane orientation and thin-film versus bulk-phase ratio, we proposed that pentacence crystalline orientation on a rubbed PI layer could be more favorable at RT, whereas the heating energy might weaken the interaction energy between pentacene molecules and aligned PI layer.

Synthesis of novel arylamine containing perfluorocyclobutane and its electrochromic properties

A new electrochromic oligomer based on an arylamine compound containing a perfluorocyclobutane (PFCB) ring has been synthesized via 2 + 2 cyclodimerization. A new N,N,N′,N′-tetraphenyl-biphenyl-4,4′-diamine (TPD) with PFCB (TPD-PFCB) showed high thermal stability with a decomposition temperature (Td) of 435 °C. Cyclic voltammograms of TPD-PFCB films coated onto an indium–tin oxide substrate showed two reversible redox steps during a potential scan between 0.7 and 1.2 V. The spectroelectrochemical series of TPD-PFCB films exhibited color change from colorless to yellow and then to greenish blue during the oxidation reaction of TPD-PFCB. This oligomer exhibited a high electrochromic coloration efficiency (602 cm2/C) and a comparable response speed (coloring and bleaching time at 700 nm were 0.71 and 0.12 s, respectively).

Effects of Copper Oxide/Gold Electrode as the Source-Drain Electrodes in Organic Thin-Film Transistors

This study examines bilayer source-drain electrodes for organic thin-film transistors (OTFTs). Between the pentacene layer and the Au layer, a p-type metal oxide layer was inserted. p-Type metal oxide was prepared by thermally evaporating copper oxide (CuO). To compare the effect of the CuO layer, a device with a single Au layer as the source-drain electrode was fabricated. The field-effect mobility of the device with the CuO (10 nm)/Au (50 nm) bilayer electrodes was 0.34 (±0.04) cm 2 /V s, and it was higher than the device with a single Au layer electrode [0.16 (±0.03) cm 2 /V s].

Perfluorocyclobutane containing polymeric gate dielectric for organic thin film transistors with high on/off ratio

A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10−3cm2∕Vs and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD=−50V.