Aza-Substituted Host Materials for OLED Efficiency and Lifetime

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Solution Overview

Problem

Achieving high external quantum efficiency and long lifetime in organic electroluminescence devices, especially when driven at low voltage, is challenging due to the difficulty in confining triplet excitons and ensuring high chemical and heat stability of materials.

Innovation Solution

A compound with an aza-substituted carbazolyl, dibenzofuranyl, or dibenzothiophenyl group structure is used as a host material, which deepens the LUMO level, facilitating carrier balance and electron injection, and is employed in the light emitting layer or as a blocking layer to confine triplet excitons, thereby enhancing the efficiency and stability of the device.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If phosphorescent emitting material is used to achieve high internal quantum efficiency, then emission efficiency increases three to four times, but achieving high efficient and long lifetime blue-phosphorescent emission becomes difficult

Engineering Contradiction:

Improveemission efficiencyVSAvoiddevice lifetime

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent modifies the chemical structure of host materials by introducing aza-substituted carbazolyl, dibenzofuranyl, or dibenzothiophenyl groups, which changes the triplet excited energy parameter to be higher than the phosphorescent dopant. This parameter change enables effective triplet exciton confinement while maintaining device lifetime, resolving the contradiction between emission efficiency and device reliability.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If triplet excitons are to be confined for high efficiency, then host material must have high triplet excited energy, but this requires specific chemical structures that may compromise carrier injecting ability

Engineering Contradiction:

Improvetriplet exciton confinement efficiencyVSAvoidcarrier injecting ability

Core Design Contradiction:

Loss of energyVSUse of energy by moving object

Solution Approach 1:

The patent employs composite material design by combining aza-substituted carbazolyl, dibenzofuranyl, or dibenzothiophenyl groups in the host material structure. This composite approach simultaneously achieves high triplet excited energy for exciton confinement and maintains good carrier injecting ability through the inherent properties of these heterocyclic groups, resolving the contradiction between exciton confinement efficiency and carrier injecting ability.

Inventive Principle:

Principle #40Composite materials

3Productivity

If material structure is modified to optimize performance, then device performance improves, but chemical and heat stability may be compromised

Engineering Contradiction:

Improvedevice performanceVSAvoidchemical and heat stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The patent applies local quality principle by strategically placing aza-substituted carbazolyl, dibenzofuranyl, or dibenzothiophenyl groups at specific positions in the host material molecule. These localized structural modifications optimize triplet excited energy and carrier transporting ability while the overall molecular framework maintains chemical and heat stability, resolving the contradiction between device performance and compositional stability.

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The use of this compound results in organic electroluminescence devices with high external quantum efficiency and extended lifetime, even when operated at low voltages, by effectively confining triplet excitons and improving carrier balance and stability.

Implementation Method 1

the phosphorescent emitting material which causes emission from triplet excitons

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

a spontaneous light emitting devices which utilize the phenomenon that a fluorescent or phosphorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 3

to have a wide gap for energetically confining the excitons of the emitting dopant

Methodology Applied

Scientific EffectEnergy level confinement:

Implementation Method 4

which deepens the LUMO level, facilitating carrier balance and electron injection

Methodology Applied

Scientific EffectElectron injection:

Data Source

PatentUS9923151B2Material for organic electroluminescent elements, and organic electroluminescent element using same

Publication Date: 2018.03.20 IDEMITSU KOSAN CO LTD

AI summary

A material for organic electroluminescence device having a specific structure, in which an aromatic ring of a dibenzofuran skeleton, a carbazole skeleton, or a dibenzothiophene skeleton has a nitrogen atom as a heteroatom, and an organic electroluminescence device including an organic thin film layer which includes one or more layers between a cathode and an anode. The organic thin film layer includes a light emitting layer which includes a phosphorescent emitting material. At least one layer of the organic thin film layer includes the material for organic electroluminescence device. The organic EL device employing the material for organic EL device has a high external quantum efficiency even when driving the device at low voltage and also has a long lifetime.