Highly efficient light-emitting materials based on
phenylquinoline-carbazole derivative has been synthesized for
organic-light emitting diodes (OLEDs). The materials form high quality amorphous thin films by thermal evaporation
and the energy levels can be easily adjusted by the introduction of different electron donating and electron withdrawing
groups on carbazoylphenylquinoline. Non-doped deep-blue OLEDs using Et-CVz-PhQ as the emitter show bright
emission (CIE coordinates, x=0.156, y=0.093) with an external quantum efficiency of 2.45 %. Furthermore, the material
works as an excellent host material for BCzVBi to get high-performance OLEDs with excellent deep-blue CIE
coordinates (x=0.155, y=0.157), high power efficiency (5.98 lm/W), and high external quantum efficiency (5.22 %).
Cyclometalated Ir(III) μ-chloride bridged dimers were synthesized by iridium trichloride hydrate with an excess of our
developed deep-blue emitter, Et-CVz-PhQ. The Ir(III) complexes were prepared by the dimers with the corresponding
ancillary ligands. The chloride bridged diiridium complexes can be easily converted to mononuclear Ir(III) complexes by
replacing the two bridging chlorides with bidentate monoanionic ancillary ligands. Among the various types of ancillary
ligands, we firstly used picolinic acid N-oxide, including picolinic acid and acetylacetone as an ancillary ligands for
Ir(III) complexes. The PhOLEDs also shows reasonably high brightness and good luminance efficiency of 20,000 cd/m2
and 12 cd/A, respectively.
Using the Gilch polymerization method, we synthesized a new series of green electroluminescent polymer, poly[1,4-{2-
(3,3'-diheptyl-3,4-propylenedioxythiophen-2-yl)}phenylenevinylene], poly(PDOT-PV), which is a series of fully
conjugated poly(p-phenylenevinylene) derivatives with a propylenedioxythiophene (PDOT) moiety as a side-chain. We
also synthesized copolymers, poly(PDOT-PV-co-m-SiPhPV), of poly(PDOT-PV) with poly[2-(3-dimethyldodecyl-
silyphenyl)-1,4-phenylenevinylene], poly(m-SiPhPV), segments. The resulting polymers were highly soluble in common
organic solvents and could be easily spin-coated onto an indium-tin oxide coated glass substrate to obtain high quality
optical thin films. The weight-average molecular weight (Mw) and polydispersity of poly(PDOT-PV) were 22.0 ×104
and 5.3, respectively, and those of poly(PDOT-PV-co-m-SiPhPV) were in the range of (23.2-36.7) ×104 and 5.0-5.8,
respectively. The stability of the resulting polymers is adequate for the fabrication of devices, and they provide longevity
to devices because they have high glass transition temperatures (Tg). We fabricated polymer light-emitting diodes
(PLEDs) in ITO/PEDOT/light-emitting polymer/cathode configurations using either double-layer LiF/Al or triple-layer
Alq3/LiF/Al cathode structures. For PLEDs containing poly(PDOT-PV) and poly(PDOT-PV-co-m-SiPhPV), the
performance was highest using triple-layer cathodes. The turn-on voltages of PDOT-based light-emitting polymers were
in the range of 6.0-9.0 V, and the maximum brightness and luminance efficiency were 5127 cd/m2 at 18 V and 3.75 cd/A
at 9 V.
A series of bis-dimethyl-n-octylsilyl end-capped oligothiophenes consisting of two to six thiophene units have been
synthesized using palladium-catalyzed Stille coupling reactions. These oligothiophenes have been characterized by 1H-,
13C-NMR and high resolution mass spectrometry. The UV-vis spectral data indicate that these silyl end-capped
oligothiophenes have longer conjugation lengths as evidenced by the higher λmax values than the corresponding
unsubstituted thiophene oligomers. The thermal analyses indicate that the bis-silylated oligothiphenes show lower
melting point (DSi-4T = 80°C; DSi-5T = 115°C; DSi-6T = 182°C) than the corresponding dialkylated thiophene
oligomers by 100°C and hexamer DSi-6T exhibits a liquid crystalline mesophase at 143°C. The α,ω-bis(dimethyl-n-octylsilyl)oligothiophenes have a remarkably high solubility in chloroform which are comparable to the corresponding
α,ω-dihexyloligothiophenes. The remarkably increased solubility by these silyl end groups leads the bis-silylated
oligothiophenes to be applicable to solution processable devices for thin film transisitor (TFT) by utilizing a spin coating
technique. We fabricated devices by spin-coating α,ω-bis(dimethyloctylsilyl)sexithiophene DSi-6T from chlorobenzene,
toluene, chloroform onto device test structures. But the OFETs using DSi-6T solved in chloroform produced the
transistor behavior. The hexamer DSi-6T, showed promising behavior as a solution-deposited semiconductor, with
mobility up to 0.014 cm2V-1s-1.
We fabricated polymer-fullerene photovoltaic (PV) devices using various conjugated polymers, poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[4-(3,7-dimethyloctyloxy)-phenoxy]-1,4-phenylenevinyl-ene} (p-DMOP-PPV), and their copolymer system, p-DMOP-co-MEH-PPV. By comparing PV characteristics of such devices with a systematic change of the energy levels (ionization potential Ip and electron affinity Ea), we investigated the origin of open circuit voltage (Voc) of the devices. Our results indicate that the magnitude of Voc is governed by the difference between Ea of the fullerene and Ip of the polymer, which is not consistent with previous consideration of the work function difference between electrodes as in conventional metal-insulator-metal type devices.
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