Hiromitsu Ogawa

Starburst molecules based on π-electron systems as materials for organic electroluminescent devices

Abstract Novel families of starburst molecules based on π-electron systems, which readily form morphologically and thermally stable, uniform amorphous films by vacuum deposition, have been found to function as excellent materials for organic electroluminescent (EL) devices. The multilayer organic EL devices consisting of double hole-transport layers and an emitting layer have been shown to exhibit high performances.

Exciplex formation at the organic solid-state interface: Yellow emission in organic light-emitting diodes using green-fluorescent tris(8-quinolinolato)aluminum and hole-transporting molecular materials with low ionization potentials

The bilayer organic light-emitting diodes using green-fluorescent tris(8-quinolinolato)aluminum (Alq3) as an emitting material and hole-transport materials with low ionization potentials, 1,3,5-tris(3-methylphenylphenylamino)triphenylamine and 4,4′,4″-tris[bis(4-tert-buthylbiphenyl4-yl)amino]triphenylamine, emitted bright yellow light instead of green light. The yellow emission is attributed to exciplex formation at the solid interface between Alq3 and the hole-transport material. The exciplex formation was evidenced by the measurement of the photoluminescence spectra and lifetimes of the mixture of an equimolar amount of Alq3 and each of the hole-transport materials. The emission color can be tuned by varying the applied voltage.

Organic light-emitting diodes using a novel family of amorphous molecular materials containing an oligothiophene moiety as colour-tunable emitting materials

A novel family of amorphous molecular materials containing an oligothiophene moiety with varying conjugation length function as thermally and morphologically stable, colour-tunable emitting materials for organic light-emitting diodes (LEDs). Tuning of the emission colour from light blue to orange is achieved by varying the conjugation length of the oligothiophene moiety. Double-layer organic LEDs that use this novel class of amorphous molecular materials as an emitting layer and tris(quinolin-8-olato)aluminium or 1,3,5-tris[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene as an electron-transport layer exhibit high performances.

A novel yellow-emitting material, 5,5′′-bis{4-[bis(4-methylphenyl)amino] phenyl}-2,2′:5′,2′′-terthiophene, for organic electroluminescent devices

A novel amorphous molecular material, 5,5′′-bis{4-[bis(4-methylphenyl)amino]phenyl}2,2′:5′,2′′-terthiophene (BMA-3T), has been found to function as a yellow-emitting material in organic electroluminescent (EL) devices. Both the single layer EL device using BMA-3T alone and the double layer EL device consisting of an emitting layer of BMA-3T and an electron-transport layer of tris(8-quinolinolato)aluminum sandwiched between indium-tin-oxide (ITO) and an alloy of magnesium and silver (∼10:1) electrodes emitted a bright yellow light resulting from BMA-3T. The double layer EL device showed much better performances than the single layer EL device, exhibiting a maximum luminance of ∼13 000 cd m−2 at a driving voltage of 18 V, and a luminous efficiency of 1.1 lm W−1 at a luminance of 300 cd m−2.

Tri(p-terphenyl-4-yl)amine as a novel blue-emitting material for organic electroluminescent devices

Abstract A novel amorphous molecular material, tri( p -terphenyl-4-yl)amine ( p -TTA), was found to function as a morphologically and thermally stable blue-emitting material for organic electroluminescent (EL) devices. A double-layer EL device consisting of an emitting layer of p -TTA and a hole-transport layer of 1,3,5-tris[ N -(4-diphenylaminophenyl)phenylamino] benzene sandwiched between an alloy of magnesium and silver (about 10:1) and indium-tin-oxide (ITO) electrodes emitted bright blue light resulting from p -TTA. The EL device exhibited a maximum luminance of about 350 cd m −2 at a driving voltage of 13 V. The external quantum efficiency was estimated to be 0.4%.

Fabrication and performances of a double-layer organic electroluminescent device using a novel starburst molecule, 1,3,5-tris[N-(4-diphenylaminophenyl)phenylamino]benzene, as a hole-transport material and tris(8-quinolinolato)aluminum as an emitting material

A double-layer organic electroluminescent (EL) device was fabricated using a novel starburst molecule, 1,3,5-tris[N-(4-diphenylaminophenyl)phenylamino]benzene (p-DPA-TDAB), as a hole transport material and tris(8-quinolinolato) aluminum (Alq/sub 3/) as an emitting material, and its performance characteristics were investigated. It was found that p-DPA-TDAB, which forms a stable amorphous glass with a glass-transition temperature of 108/spl deg/C, functions as a good hole-transport material and that the EL device is thermally stable, operating at a temperature of 120/spl deg/C.

Exciplex Emission in an Organic Electroluminescent Device Using Electron-transporting 1,3,5-Tris(4-tert−butylphenyl-1,3,4-oxadiazolyl)benzene and Hole-transporting N,N′−bis(3-methylphenyl)-N,N′−diphenyl-[1,l′-biphenyl]-4,4′-diamine

Abstract Exciplex formation at the organic solid-state interface in an organic electroluminescent device has been studied. A new multilayer device consisting of the electron-transport layer of 1,3,5-tris(4-tert−butylphenyl-1,3,4-oxiadiazolyl)benzene (TPOB) and double hole-transport layers of 4,4′,4′-tris(3-methylphenylphenylamino)triphenylamine (m−MTDATA) and N,N′−bis-(3-methylphenyl)-N,N′−diphenyl-[1,l′-biphenyl]-4,4′-diamine (TPD) sandwiched between the electrodes of an alloy of magnesium and silver and indium tin oxide (ITO) emitted bright bluish-green light resulting from the exciplex formed at the interface between TPOB and TPD. The exciplex formation is evidenced by the measurement of the photoluminescence spectra of spin-coated films of TPOB, TPD, and a mixture of TPOB and TPD and their photoluminescence lifetimes.