Thermally Activated Delayed Fluorescence Material for OLEDs

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Solution Overview

Problem

Current thermally activated delayed fluorescence materials are scarce, limiting the development of highly efficient organic light-emitting diodes (OLEDs) with 100% internal quantum efficiency, particularly for blue light-emitting materials, due to high singlet-triplet energy gaps and low reverse intersystem crossover constants.

Innovation Solution

A novel thermally activated delayed fluorescence material with a specific molecular structure, represented by formulas (I), (II), and (III), is synthesized, featuring lower singlet-triplet energy gaps and higher reverse intersystem crossover constants, enhancing photoluminescence quantum yields and light-emitting efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If heavy metal complex phosphorescence materials are used to achieve 100% internal quantum efficiency, then light-emitting efficiency is improved, but cost increases due to precious metals such as iridium and platinum

Engineering Contradiction:

Improvelight-emitting efficiencyVSAvoidcost of precious metals

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The patent replaces expensive precious metal complexes with purely organic TADF materials that are cheaper and can be synthesized more easily, achieving the same functional goal of high internal quantum efficiency without relying on iridium or platinum

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent modifies molecular parameters by designing organic compounds with specific donor-acceptor structures that achieve low singlet-triplet energy gaps and high reverse intersystem crossing rates, enabling TADF behavior without heavy metals

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If conventional fluorescence materials are used in OLEDs, then material simplicity is maintained, but internal quantum efficiency is limited to 25% due to 1:3 ratio of singlet to triplet excitons

Engineering Contradiction:

Improvematerial simplicityVSAvoidinternal quantum efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent changes the energy gap parameter (ΔEST) to be very small in the TADF materials, enabling thermal energy to facilitate reverse intersystem crossing from triplet to singlet state, thereby utilizing both singlet and triplet excitons for light emission

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent utilizes periodic thermal activation to enable reverse intersystem crossing, where thermal energy periodically promotes triplet excitons back to singlet state, allowing continuous utilization of triplet excitons for delayed fluorescence emission

Inventive Principle:

Principle #19Periodic action

3Speed

If thermally activated delayed fluorescence materials with low singlet-triplet energy gap are designed, then reverse intersystem crossing rate is improved, but synthesis complexity increases

Engineering Contradiction:

Improvereverse intersystem crossing rateVSAvoidsynthesis complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent divides the molecule into separate electron-donating and electron-accepting units, allowing independent optimization of each unit's properties while achieving the desired low energy gap and high RISC rate through their combination

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent creates composite molecular structures combining electron-donating groups (such as carbazole, triphen胺) with electron-accepting groups (such as pyridine, pyrimidine), achieving synergistic effects that facilitate rapid reverse intersystem crossing

Inventive Principle:

Principle #40Composite materials

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 new material achieves high light-emitting efficiency in OLEDs, enabling blue, green, and red light-emitting diodes with improved performance, suitable for various display and electronic devices, with synthesis methods providing high yields and efficient production.

Implementation Method 1

triplet excitons can return to singlet state through reverse intersystem crossing (RISC), and then radiatively transit to ground state to emit light

Methodology Applied

Scientific EffectReverse intersystem crossing:

Implementation Method 2

high photoluminescence quantum yields (PLQYs)

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Implementation Method 3

Thermally activated delayed fluorescence (TADF) material has a low singlet-triplet energy gap (ΔEST). Therefore, triplet excitons can return to singlet state through reverse intersystem crossing (RISC)

Methodology Applied

Scientific EffectThermal activation:

Data Source

PatentUS11430959B2Thermally activated delayed fluorescence material and organic light-emitting diode prepared using same

Publication Date: 2022.08.30 WUHAN CHINA STAR OPTOELECTRONICS SEMICONDUCTOR DISPLAY TECHNOLOGY CO LTD

AI summary

The present disclosure provides a thermally activated delayed fluorescence material having a structure of formula (I) and having a low single-triplet energy gap, a high reverse intersystem crossover constant, and a high photoluminescence quantum yield.Furthermore, the present disclosure provides an organic light emitting diode including an anode, a cathode, and a light emitting layer disposed between the anode and the cathode. The light emitting layer includes the thermally activated delayed fluorescence material having the structure of formula (I).