Organic Electroluminescence Device Delayed Fluorescent Emission Layer

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Solution Overview

Problem

Current organic electroluminescence devices face limitations in luminous efficiency, particularly in high current density regions, as they primarily utilize singlet excitons and struggle to effectively harness triplet excitons.

Innovation Solution

Incorporating a delayed-fluorescent compound and a second compound with specific partial structures in the emitting layer of the organic electroluminescence device, which facilitates thermally activated delayed fluorescence (TADF) by minimizing the energy gap between singlet and triplet states, enabling efficient inverse intersystem crossing and enhanced luminous efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fluorescent organic EL device uses only singlet excitons for emission, then the device structure is simple, but the internal quantum efficiency is limited to 25% at maximum

Engineering Contradiction:

Improvedevice structureVSAvoidinternal quantum efficiency

Core Design Contradiction:

Device complexityVSUse of energy by moving object

Solution Approach 1:

The invention changes the energy parameter by introducing a delayed-fluorescent compound with specific energy level characteristics (small energy gap between singlet and triplet states) to enable thermal activation of triplet excitons, thereby converting non-emissive triplet excitons into emissive singlet excitons and achieving internal quantum efficiency exceeding 25%

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses a composite emitting layer comprising both the delayed-fluorescent compound (formula 1) and the second compound (formula 21 or 22). The delayed-fluorescent compound facilitates triplet-to-singlet conversion while the second compound provides structural stability and enhances the TADF effect, together achieving high internal quantum efficiency

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If triplet excitons are utilized through TADF mechanism, then internal quantum efficiency is enhanced, but luminous efficiency deteriorates in high current density regions

Engineering Contradiction:

Improveinternal quantum efficiencyVSAvoidluminous efficiency in high current density region

Core Design Contradiction:

Use of energy by moving objectVSProductivity

Solution Approach 1:

The invention optimizes the local composition of the emitting layer by precisely controlling the doping concentration of the delayed-fluorescent compound (0.1-10 wt%) and the second compound (90-99.9 wt%). This local optimization ensures efficient TADF at high current densities without causing efficiency roll-off, as the specific composition ratio maintains balanced charge injection and recombination

Inventive Principle:

Principle #3Local quality

3Use of energy by moving object

If the energy gap between singlet and triplet states is minimized for TADF, then inverse intersystem crossing is enhanced, but manufacturing precision requirements increase

Engineering Contradiction:

Improveinverse intersystem crossing efficiencyVSAvoidcompound structure precision

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The invention achieves the desired small energy gap (ΔEST ≤ 0.2 eV) by systematically modifying molecular parameters: introducing electron-donating groups (Ar11, Ar12) and electron-withdrawing groups (X1) at specific positions, and adjusting the linking group (L1) structure. These parameter changes enable precise control over energy levels while maintaining structural stability and ease of synthesis

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 proposed solution significantly improves luminous efficiency in high current density regions by effectively utilizing both singlet and triplet excitons, potentially increasing internal quantum efficiency up to 100% through delayed fluorescence mechanisms.

Implementation Method 1

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

Methodology Applied

Scientific EffectThermally activated delayed fluorescence (TADF):

Implementation Method 2

inverse intersystem crossing from triplet excitons to singlet excitons is thermally generated

Methodology Applied

Scientific EffectInverse intersystem crossing:

Implementation Method 3

When a voltage is applied to an organic electroluminescence device, holes are injected from an anode into an emitting layer and electrons are injected from a cathode into the emitting layer. The injected electrons and holes are recombined in an emitting layer to form excitons.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS10249826B2Compound, organic electroluminescent element and electronic device

Publication Date: 2019.04.02 IDEMITSU KOSAN CO LTD

AI summary

An organic electroluminescence device includes an anode, an emitting layer and a cathode, in which the emitting layer includes a first compound and a second compound. The first compound is a delayed-fluorescent compound represented by a formula (1) below. The second compound includes at least one of a partial structure represented by a formula (21) below and a partial structure represented by a formula (22) below in one molecule.