Phosphorescent Stack Host Material for OLED Efficiency

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Solution Overview

Problem

Current light emitting devices in displays face limitations in efficiency and stability due to differences in emission colors and principles between stacks, leading to reduced reliability when trying to enhance efficiency by changing materials.

Innovation Solution

A light emitting device with a phosphorescent stack configuration that includes a hole transport layer and a red light emitting layer, where the red light emitting layer features an electron transport host and a hole transport host different from the hole transport layer, optimized to improve exciton efficiency and stability, using specific compounds like benzocarbazole-based materials to prevent exciton loss and ensure thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If materials are changed to increase efficiency in light emitting devices, then emission efficiency is improved, but reliability is lowered due to lack of consideration for stability

Engineering Contradiction:

Improveemission efficiencyVSAvoiddevice stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent modifies the chemical structure parameters of the host material by introducing specific substituents (aromatic rings, aryl groups, biphenyl groups, and heteroatoms N/O/S) to optimize both efficiency and stability. This structural parameter change allows the material to achieve high emission efficiency while maintaining long-term operational stability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material design by combining the benzocarbazole-based host material with specific dopants and integrating it into a multi-layer phosphorescent stack structure. This composite approach enables the device to achieve both high efficiency and reliability by leveraging the synergistic effects of different materials.

Inventive Principle:

Principle #40Composite materials

2Productivity

If a plurality of stacks are used to improve efficiency, then emission efficiency is increased, but the extent of efficiency increase is limited due to differences in emission colors and emission principles between each stack

Engineering Contradiction:

Improveemission efficiencyVSAvoidstack configuration complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent merges multiple light emitting functions into a single phosphorescent stack structure. By incorporating red, green, and blue light emitting layers within one stack, the device achieves high overall efficiency without the limitations of coordinating multiple separate stacks, while also simplifying the device architecture.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The phosphorescent stack structure serves multiple functions simultaneously - it generates red, green, and blue light through a single integrated structure, eliminating the need for separate stacks for each color and overcoming the efficiency limitations imposed by inter-stack variations.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If exciton efficiency is improved for one color, then that color's emission is enhanced, but other colors may suffer from exciton loss due to interface issues with the hole transport layer

Engineering Contradiction:

Improvecolor-specific emission efficiencyVSAvoidexciton loss at interface

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent applies local quality optimization by designing the hole transport layer with specific functional characteristics that are tailored to work effectively with all three phosphorescent light emitting layers (red, green, and blue). The layer's material composition and properties are locally optimized at each interface to prevent exciton loss while maintaining high efficiency for all color emissions.

Inventive Principle:

Principle #3Local quality

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 enhances the efficiency of white light emission by balancing the exciton efficiency for each color, prolonging the lifespan of the device and improving the overall luminance of the display without the need for compensation, thereby increasing the reliability and efficiency of the light emitting display.

Implementation Method 1

a phosphorescent stack disposed between the first electrode and the second electrode, wherein the phosphorescent stack includes a hole transport layer, a red light emitting layer, a green light emitting layer, and an electron transport layer

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

the red light emitting layer includes an electron transport host represented by Formula 1, a hole transport host different from the hole transport layer, and a red dopant

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Data Source

PatentUS20230217669A1Light emitting device and light emitting display including the same

Publication Date: 2023.07.06 LG DISPLAY CO LTD

AI summary

A light emitting device including a first electrode and a second electrode facing each other, and a first blue stack, a first charge generation layer, and a phosphorescent stack disposed between the first electrode and the second electrode. The phosphorescent stack includes a hole transport layer, a red light emitting layer, a green light emitting layer, and an electron transport layer. The red light emitting layer includes an electron transport host represented by Formula 1, a hole transport host different from the hole transport layer, and a red dopant.