Organic Electroluminescent Element Using TADF Compounds

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing organic electroluminescence devices face challenges in achieving high internal quantum efficiency and require higher drive voltages, which limits their practical application.

Innovation Solution

An organic electroluminescence device is designed with an emitting layer comprising a first and second compound that emit thermally activated delayed fluorescence, with a small energy gap between their singlet and triplet states, allowing for efficient inverse intersystem crossing and reduced drive voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If a fluorescent EL device uses emission caused by singlet excitons, then the device structure is simpler and lifetime is improved, but the internal quantum efficiency is limited to 25%

Engineering Contradiction:

Improvedevice lifetimeVSAvoidinternal quantum efficiency

Core Design Contradiction:

Duration of action of stationary objectVSUse of energy by moving object

Solution Approach 1:

The patent changes the energy parameters of the luminescent material by selecting compounds with specific singlet and triplet energy levels where the energy gap is small (less than 2.1 eV). This parameter change enables efficient inverse intersystem crossing from triplet to singlet excitons, allowing delayed fluorescence to convert the typically lost 75% triplet excitons into useful singlet excitons for fluorescence emission, thereby achieving internal quantum efficiency exceeding 25% while maintaining fluorescent device simplicity and long lifetime.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If a phosphorescent EL device uses emission caused by triplet excitons, then the internal quantum efficiency can be improved up to 100%, but the device requires expensive transition metal complexes and has shorter lifetime

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoiddevice lifetime

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The patent replaces expensive phosphorescent materials containing transition metal complexes with cheap organic fluorescent compounds that exhibit delayed fluorescence. By selecting luminescent materials with appropriate energy level structures (small singlet-triplet energy gap), the device achieves high internal quantum efficiency through a different mechanism (delayed fluorescence via inverse intersystem crossing) that does not require costly metals, thereby reducing material cost and extending device lifetime while maintaining comparable efficiency.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Use of energy by moving object

If delayed fluorescence by TTF mechanism is used, then the internal quantum efficiency can be raised up to 40%, but the drive voltage remains high and lifetime is limited

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoiddrive voltage

Core Design Contradiction:

Use of energy by moving objectVSPower

Solution Approach 1:

The patent optimizes the energy level parameters of the luminescent material, specifically selecting compounds with small singlet-triplet energy gaps (less than 2.1 eV). This parameter optimization enables more efficient inverse intersystem crossing and delayed fluorescence emission, achieving internal quantum efficiency exceeding 40% while reducing the energy barrier for exciton conversion. The improved efficiency reduces the drive voltage requirement compared to conventional fluorescent devices, and the stable organic material structure extends device lifetime.

Inventive Principle:

Principle #35Parameter changes

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 device achieves a longer lifetime and lower drive voltage while maintaining luminous efficiency comparable to phosphorescent devices without using expensive transition metal complexes.

Implementation Method 1

each of the first compound and the second compound is a compound emitting thermally activated delayed fluorescence

Methodology Applied

Scientific EffectThermally activated delayed fluorescence: Fluorescence

Implementation Method 2

The TADF mechanism utilizes a phenomenon in which inverse intersystem crossing from triplet excitons to singlet excitons is generated by using a material having a small energy gap (ΔST) between the singlet energy level and the triplet energy level

Methodology Applied

Scientific EffectInverse intersystem crossing: Fluorescence

Implementation Method 3

Methodology Applied

Scientific EffectThermal activation: Heating

Data Source

PatentUS10186665B2Organic electroluminescent element

Publication Date: 2019.01.22 IDEMITSU KOSAN CO LTD

AI summary

An organic electroluminescence device includes an anode, a cathode and an emitting layer, in which the emitting layer includes a first compound and a second compound and each of the first compound and the second compound is a compound emitting thermally activated delayed fluorescence.