OLED Delayed Fluorescent Layer Triplet Singlet Conversion

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Solution Overview

Problem

Organic light emitting diodes (OLEDs) using fluorescent materials have low quantum efficiency due to the limited involvement of triplet excitons in light emission, while those using phosphorescent materials are limited by iridium complex design and blue emission limitations.

Innovation Solution

An OLED structure incorporating a delayed fluorescent material layer with a singlet energy greater than the triplet energy, allowing for the activation of triplet excitons into singlet excitons for enhanced light emission efficiency, and a layered structure combining delayed fluorescent and fluorescent materials to balance quantum efficiency and color purity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If fluorescent material is used in the emitting material layer, then the OLED is applicable to blue emission and has less limit to dopant design, but only singlet exciton is involved in light emission resulting in low quantum efficiency

Engineering Contradiction:

Improvedopant design flexibilityVSAvoidquantum efficiency

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent employs a composite emitting material layer comprising both fluorescent and phosphorescent materials. The fluorescent material provides blue emission capability and dopant design flexibility, while the phosphorescent material enables triplet exciton utilization. This composite structure allows both singlet and triplet excitons to contribute to light emission, achieving high quantum efficiency while maintaining the advantages of fluorescent materials.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If phosphorescent material is used in the emitting material layer, then both singlet and triplet excitons are involved in light emission resulting in high light emission efficiency, but there are limits to iridium complex design and blue emission

Engineering Contradiction:

Improvequantum efficiencyVSAvoidemission color range

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The patent creates a composite emitting material layer that combines fluorescent and phosphorescent materials. The fluorescent component enables blue emission and flexible dopant design, while the phosphorescent component ensures high quantum efficiency through triplet exciton utilization. This composite approach overcomes the limitations of pure phosphorescent materials regarding blue emission and iridium complex design constraints.

Inventive Principle:

Principle #40Composite materials

3Device complexity

If a single emitting material layer is used, then the device structure is simple, but it cannot simultaneously achieve high quantum efficiency and narrow full width at half maximum

Engineering Contradiction:

Improveemitting layer structureVSAvoidcolor purity

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent divides the emitting material layer into multiple sub-layers with different functions. One sub-layer is optimized for high quantum efficiency (utilizing both singlet and triplet excitons), while another sub-layer is optimized for narrow full width at half maximum (color purity). This segmentation allows each sub-layer to specialize in one performance aspect, and the combination achieves both high quantum efficiency and narrow FWHM simultaneously.

Inventive Principle:

Principle #1Segmentation

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 solution improves quantum efficiency and maintains high brightness without increasing driving voltage, while also narrowing the full width at half maximum to enhance color purity in OLEDs.

Implementation Method 1

the first layer includes a first compound, and the second layer includes a second compound, wherein the first compound has a difference, between a singlet energy and a triplet energy, less than 0.3 eV

Methodology Applied

Scientific EffectReverse intersystem crossing:

Implementation Method 2

Methodology Applied

Scientific EffectDelayed fluorescence:

Implementation Method 3

when an electrode and a hole are injected to an emitting material layer formed between an electron injection electrode (cathode) and a hole injection electrode (anode), an electrode-hole pair is generated then disappears to emit a light

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 4

The fluorescent material has a less limit to a dopant and is applicable to a blue emission. However, in the fluorescent material, only a singlet exciton is involved to a light emission

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Data Source

PatentUS10566561B2Organic light emitting diode and organic light emitting display device including the same

Publication Date: 2020.02.18 LG DISPLAY CO LTD

AI summary

An organic light emitting diode includes an emitting material layer including first and second layers; a first electrode on a side of the emitting material layer; and a second electrode on the other side of the light emitting material layer and facing the first electrode, wherein the first layer includes a first compound, and the second layer includes a second compound, wherein the first compound has a difference, between a singlet energy and a triplet energy, less than 0.3 eV, and wherein the singlet energy of the first compound is greater than a singlet energy of the second compound.