Blue organic light-emitting diodes that harness thermally activated delayed fluorescence are realized with an external quantum efficiency of 19.5% and reduced roll-off at high luminance.

Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence

Functional π-Gelators and Their Applications

On the basis of theoretical models and calculations, several alternating polymeric structures have been investigated to develop optimized poly(2,7-carbazole) derivatives for solar cell applications. Selected low band gap alternating copolymers have been obtained via a Suzuki coupling reaction. A good correlation between DFT theoretical calculations performed on model compounds and the experimental HOMO, LUMO, and band gap energies of the corresponding polymers has been obtained. This study reveals that the alternating copolymer HOMO energy level is mainly fixed by the carbazole moiety, whereas the LUMO energy level is mainly related to the nature of the electron-withdrawing comonomer. However, solar cell performances are not solely driven by the energy levels of the materials. Clearly, the molecular weight and the overall organization of the polymers are other important key parameters to consider when developing new polymers for solar cells. Preliminary measurements have revealed hole mobilities of about ...

Toward a rational design of poly(2,7-carbazole) derivatives for solar cells.

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

Recent Progresses on Materials for Electrophosphorescent Organic Light-Emitting Devices

Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C−N)3, where (C−N) is a monoanionic cyclometalating ligand:  2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows:  quantum yields of phosphorescence Φp = 0.08−0.29, emission peaks λmax = 558−652 nm, and emission lifetimes τ = 0.74−4.7 μs. Bathochromic shifts of the Ir(thpy)3 family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Φp of the red em...

Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode.

A luminescence device is principally constituted by a pair of electrodes and an organic compound layer disposed therebetween. The layer contains a metal coordination compound represented by the following formula (1):

Luminescence device, display apparatus and metal coordination compound

In order to improve the light emission efficiency and the light emission life time of an organic electroluminescent device, the invention provides a method for improving the dispersibility of a light emitting material in the light emitting layer. The light emitting device comprises electrodes consisting of an anode and a cathode provided on a substrate, and an organic light emitting layer between the electrodes, wherein the organic light emitting layer includes a light emitting material and a dopant for improving the dispersibility thereof. As the dopant, there are employed a light emitting compound and a non-light emitting compound or a current enhancing material. In case of employing the light emitting compound, the composition corresponds to a case of utilizing plural light emitting materials, and, in such case, the light emission wavelengths are preferably mutually closer. Also evaporation of the light emitting material and the dopant in a same evaporation boat allows to reduce the evaporation temperature, to improve the dispersibility of the light emitting material and to improve the device characteristics. In this manner there can be obtained a light emitting device of a high light emission efficiency and a long light emission life.

Organic electroluminescent device

A metal coordination compound suitable as an organic material for a luminescent device is represented by the following formula (1):

Metal coordination compound, luminescence device and display apparatus

Studies on synthesis, structures, and photophysics have been carried out for a series of luminescent copper(I) halide complexes with the chelating ligand, 1,2-bis[diphenylphosphino]benzene (dppb). The complexes studied are halogen-bridged dinuclear complexes, [Cu(mu-X)dppb]2 (X = I (1), Br (2), Cl (3)), and a mononuclear complex, CuI(dppb)(PPh3) (4). These complexes in the solid state exhibit intense blue-green photoluminescence with microsecond lifetimes (emission peaks, lambdamax = 492-533 nm; quantum yields, Phi = 0.6-0.8; and lifetimes, tau = 4.0-10.4 mus) at 298 K. In 2-methyltetrahydrofuran (2mTHF) solutions at 298 K, only 1 and 4 show weaker emission (Phi = 0.009) with shorter lifetimes (tau = 0.35 and 0.23 mus) and red-shifted spectra (lambdamax = 543 and 546 nm). The emission in the solid state originates from the (M + X)LCT excited state with a distorted-tetrahedral conformation, in which emissive excited states, 1(M + X)LCT and 3(M + X)LCT, are in equilibrium with an energy difference of approximately 2 kcal/mol. On the other hand, the complexes in the 2mTHF solutions emit from the MLCT excited state with an energetically favorable flattened conformation in the temperature range of 298-130 K. The flattened geometry with equilibrated 1MLCT and 3MLCT states has a nonradiative rate at least 2 orders of magnitude larger than that of the distorted-tetrahedral geometry, leading to a much smaller emission quantum yield (Phi = 0.009) at 298 K. Since the flattening motion is markedly suppressed below 130 K, the emission observed in 2mTHF below 130 K is considered to occur principally from the (M + X)LCT state with a distorted-tetrahedral geometry. To interpret the photophysics of 1 and 4 in both the solid and solution states, we have proposed the "2-conformations with 2-spin-states model (2C x 2S model)". The electroluminescence device using (1) as a green emissive dopant showed a moderate EL efficiency; luminous efficiency = 10.4 cd/A, power efficiency = 4.2 lm/W at 93 cd/m(2), and maximum external quantum efficiency = 4.8%.

Akira Tsuboyama

Papers

Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode.

Luminescence device, display apparatus and metal coordination compound

Organic electroluminescent device

Metal coordination compound, luminescence device and display apparatus

Photophysical properties of highly luminescent copper(I) halide complexes chelated with 1,2-bis(diphenylphosphino)benzene.