OLED Emission Layer Dopant Mixing for Efficiency and Color Purity

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Solution Overview

Problem

Conventional organic light emitting display devices have low luminous efficiency due to the limited participation of triplet excitons in light emission, and blue phosphorescent materials suffer from low color purity, limiting their application in display devices.

Innovation Solution

An organic light emitting diode is developed with an emission layer formed by mixing a fluorescent dopant and a phosphorescent dopant, where the phosphorescent dopant is modified with a substituent serving as an acceptor to shift its emission peak to a short wavelength range, enhancing energy transfer efficiency and overlapping with the absorption peak of the fluorescent dopant.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a phosphorescent material is used as a dopant to improve luminous efficiency, then the luminous efficiency increases, but the lifespan decreases

Engineering Contradiction:

Improveluminous efficiencyVSAvoidlifespan

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The emission layer combines both phosphorescent dopant (for high luminous efficiency through triplet exciton utilization) and fluorescent dopant (for extended lifespan) in a single system. The phosphorescent dopant converts singlet excitons to triplet excitons via intersystem crossing, while the fluorescent dopant receives energy transfer from triplet excitons and emits light, achieving both high efficiency and long operational life simultaneously

Inventive Principle:

Principle #5Merging (Combining)

2Use of energy by moving object

If a blue phosphorescent material is used to achieve short wavelength emission, then the luminous efficiency improves, but the color purity decreases

Engineering Contradiction:

Improveluminous efficiencyVSAvoidcolor purity

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The fluorescent dopant acts as an intermediary that receives energy from the phosphorescent dopant and re-emits it at a specific wavelength. The phosphorescent dopant (with broad emission spectrum) transfers energy to the fluorescent dopant, which then emits light with narrow bandwidth and high color purity, solving the color purity problem while maintaining high luminous efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If the emission peak of phosphorescent dopant is shifted to short wavelength to overlap with fluorescent dopant absorption peak, then the energy transfer efficiency improves, but the energy loss increases

Engineering Contradiction:

Improveenergy transfer efficiencyVSAvoidenergy loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The phosphorescent dopant is modified by introducing electron-withdrawing substituents (cyano, nitro, halogen groups) at specific positions (a3, a5, or a6) to change its energy level parameters. This shifts the emission peak wavelength to 480-530 nm range, creating optimal overlap with the fluorescent dopant's absorption peak and maximizing energy transfer efficiency while minimizing energy loss through non-radiative transitions

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

This configuration improves luminous efficiency by minimizing energy loss and allowing the organic light emitting diode to be driven at low voltage, while maintaining color purity and efficiency in display devices.

Implementation Method 1

A phosphorescent material can convert singlet excitons into triplet excitons through intersystem crossing (ISC), and energy in a triplet state can be transferred to a ground state due to strong spin-orbit coupling by the heavy metal

Methodology Applied

Scientific EffectIntersystem crossing:

Implementation Method 2

energy in a triplet state can be transferred to a ground state due to strong spin-orbit coupling by the heavy metal

Methodology Applied

Scientific EffectSpin-orbit coupling:

Implementation Method 3

When holes and electrons recombine to form excitons, singlet excitons in a paired spin state and triplet excitons in an unpaired spin state are generated in a ratio of 1:3 depending on spin configurations

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Data Source

PatentUS20230209987A1Organic light emitting diode and organic light emitting display device having the same

Publication Date: 2023.06.29 LG DISPLAY CO LTD

AI summary

An organic light emitting diode includes an anode, an emission layer disposed on the anode and including a host, a phosphorescent dopant represented by Chemical Formula 1 and a fluorescent dopant represented by Chemical Formula 2, and a cathode disposed on the emission layer formed by mixing the fluorescent dopant with the phosphorescent dopant bonded to an acceptor at a specific site, thereby energy loss during an emission process can be minimized and energy transfer efficiency can be improved, and an organic light emitting diode with improved luminous efficiency and an organic light emitting display device having the same can be provided.