Delayed Fluorescence Compound for OLED Efficiency

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Solution Overview

Problem

Current OLEDs using fluorescent compounds have limited emitting efficiency, particularly for blue phosphorescent compounds, which fail to meet requirements in terms of efficiency and reliability, resulting in maximum emitting efficiency of less than approximately 5% due to the exclusion of triplet excitons from the emission process.

Innovation Solution

A delayed fluorescence compound is developed, incorporating a first electron donor moiety of indolo-[3,2,1-j,k]carbazole, a second electron donor moiety such as indolo-[3,2,1-j,k]carbazole or triphenylamine, and an electron acceptor moiety like dibenzothiophene sulfone, which are combined to enhance charge transfer and dipole moment, allowing both singlet and triplet excitons to engage in emission, thereby improving efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If fluorescent compounds are used as emitting materials in OLEDs, then the device structure is simple and manufacturing is easier, but the emitting efficiency is limited to less than 5% due to exclusion of triplet excitons

Engineering Contradiction:

Improveease of manufactureVSAvoidemitting efficiency

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The patent changes the quantum mechanical parameter of spin selection rules by using delayed fluorescence mechanism. Triplet excitons are converted to singlet excitons through thermal energy and electric field assistance, allowing them to participate in emission. This parameter change enables both singlet and triplet excitons to contribute to light emission, achieving theoretical quantum efficiency of 100% while maintaining fluorescent compound simplicity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material strategy by combining delayed fluorescence emitters with specific host materials that facilitate triplet-to-singlet conversion. The host-guest system creates a composite structure where the host provides the necessary energy transfer pathways and the guest (delayed fluorescence emitter) provides the emission function, resolving the contradiction between manufacturing simplicity and emitting efficiency

Inventive Principle:

Principle #40Composite materials

2Productivity

If phosphorescent compounds are used to engage both singlet and triplet excitons in emission, then the emitting efficiency improves, but the device complexity increases and reliability of blue emission is insufficient

Engineering Contradiction:

Improveemitting efficiencyVSAvoiddevice complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent changes the emission mechanism parameter from phosphorescence (forbidden transition) to delayed fluorescence (allowed transition with thermal assistance). This parameter change maintains high emitting efficiency by engaging both singlet and triplet excitons while avoiding the complexity and reliability issues associated with phosphorescent materials, particularly for blue emission where phosphorescent compounds remain underdeveloped

Inventive Principle:

Principle #35Parameter changes

3Productivity

If phosphorescent compounds are used for blue emission, then the emitting efficiency may improve, but the reliability is insufficient

Engineering Contradiction:

Improveemitting efficiencyVSAvoidreliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the emission mechanism from phosphorescence to delayed fluorescence, which has faster decay times and avoids the long-lived triplet states that cause reliability issues in phosphorescent OLEDs. The delayed fluorescence mechanism achieves high efficiency while maintaining the stability and reliability of fluorescent materials, particularly for blue emission where phosphorescent compounds lack sufficient reliability

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 delayed fluorescence compound achieves a theoretical quantum efficiency of 100% by activating triplet excitons and engaging both singlet and triplet excitons in the emission process, significantly enhancing the emitting efficiency of OLEDs and improving color purity and thermal stability.

Implementation Method 1

Methodology Applied

Scientific EffectDelayed fluorescence: Fluorescence

Implementation Method 2

which are combined to enhance charge transfer and dipole moment, allowing both singlet and triplet excitons to engage in emission

Methodology Applied

Scientific EffectCharge transfer:

Data Source

PatentUS9837619B2Delayed fluorescence compound, and organic light emitting diode and display device using the same

Publication Date: 2017.12.05 LG DISPLAY CO LTD

AI summary

Discussed is a delayed fluorescence compound including a first electron donor moiety of indolo-[3,2,1-j,k]carbazole; a second electron donor moiety selected from indolo-[3,2,1-j,k]carbazole, carbazole, or triphenylamine; and an electron acceptor moiety selected from dibenzothiophene sulfone or diphenyl sulfone, wherein the first and second electron donor moieties are combined to the electron acceptor moiety, and the electron acceptor moiety is combined to a third position or a sixth position of the first electron donor moiety.