Organic Electroluminescence Device Hole Transporting Zone Light Extraction

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Solution Overview

Problem

Organic electroluminescence devices face low light-extraction efficiency due to refractive index differences between layers, leading to significant light emission loss.

Innovation Solution

Incorporating a hole transporting zone with a first anode side organic layer and a second anode side organic layer, where the first layer has a higher refractive index than the second layer, and adjusting their thickness and composition to optimize light extraction, particularly using a total film thickness of 20 nm to 80 nm, and ensuring the first layer contains a mixture of different organic materials with the second layer containing a single compound.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single-layer hole transporting zone is used, then the device structure is simple, but light-extraction efficiency is low due to reflection losses from refractive index differences

Engineering Contradiction:

Improvestructure simplicityVSAvoidlight emission loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The hole transporting zone is divided into multiple organic layers with different refractive indices. The first organic layer (adjacent to anode) has a higher refractive index than the second organic layer (adjacent to emitting layer), creating a gradient structure that reduces reflection losses and improves light extraction efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the hole transporting zone are assigned different refractive indices to optimize light extraction at specific interfaces. The first organic layer uses materials with higher refractive index near the anode, while the second organic layer uses materials with lower refractive index near the emitting layer, creating localized optical properties that minimize reflection.

Inventive Principle:

Principle #3Local quality

2Loss of energy

If organic layers with low refractive index are used to reduce reflection, then light-extraction efficiency improves, but hole supply property may be insufficient

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidhole supply property

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The hole transporting zone uses composite organic layer structures where each layer is formed from different organic materials with complementary properties. The first organic layer uses materials optimized for hole transport and higher refractive index, while the second organic layer uses materials with lower refractive index and appropriate hole transport capability, creating a composite structure that satisfies both optical and electrical requirements.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The refractive index parameter is varied across different organic layers to optimize light extraction. By selecting organic materials with different refractive indices for the first and second layers, the structure creates a refractive index gradient that reduces reflection losses while maintaining adequate hole supply through proper material selection in each layer.

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 enhances light-extraction efficiency by reducing losses in both evanescent and thin film modes, improving the overall luminous efficiency of the organic electroluminescence device.

Implementation Method 1

decay due to the reflection caused by the difference between refractive indices of adjacent layers is a major factor in reducing the light-extraction efficiency

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

decay due to the reflection caused by the difference between refractive indices of adjacent layers

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11575087B1Organic electroluminescence device, light emitting device, organic electroluminescence display device and electronic device

Publication Date: 2023.02.07 IDEMITSU KOSAN CO LTD

AI summary

An organic electroluminescence device includes: an emitting region provided between a cathode and an anode; and a hole transporting zone provided between the anode and the emitting region, in which the hole transporting zone includes at least a first anode side organic layer and a second anode side organic layer, the first anode side organic layer is in direct contact with the second anode side organic layer, a total film thickness of the hole transporting zone is in a range from 20 nm to 80 nm, the first anode side organic layer contains no compound contained in the second anode side organic layer, the first anode side organic layer contains a first organic material and a second organic material, the first organic material is different from the second organic material, and a content of the first organic material in the first anode side organic layer is less than 50 mass %.