Organic EL Capping Layer Chemistry for Light Extraction and Color Purity

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Solution Overview

Problem

Existing organic electroluminescent (EL) devices face challenges in improving light extraction efficiency, particularly in top-emission structures, due to limitations in materials used for capping layers, which affect refractive index, durability, and color purity.

Innovation Solution

The use of amine compounds with specific benzofuran or benzothiophene structures as capping layer materials, offering high refractive index, excellent thin film stability, durability, and no absorption in blue, green, or red wavelength regions, enhancing light extraction efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If conventional capping layer materials (e.g., ZnSe, Alq3) are used, then light extraction efficiency can be improved to some extent, but the materials suffer from poor thin film stability, absorption in blue/green wavelengths, and reduced device lifetime

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidthin film stability and device lifetime

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent changes the chemical structure parameters of the capping layer material by introducing specific benzofuran or benzothiophene moieties with conjugated aromatic rings. This structural parameter change enables the material to achieve both high refractive index (for light extraction) and excellent stability (for reliability), resolving the contradiction between light extraction efficiency and thin film stability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite molecular structure combining amine groups with benzofuran or benzothiophene cores, creating a material that integrates multiple desirable properties: high refractive index from the aromatic system, stability from the fused ring structure, and appropriate optical properties from the amine functionality. This composite approach allows simultaneous optimization of light extraction and device reliability

Inventive Principle:

Principle #40Composite materials

2Illumination intensity

If capping layer materials with high refractive index are used to improve light extraction, then light extraction efficiency increases, but absorption in blue and green wavelength regions reduces color purity

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoidabsorption in blue and green wavelengths

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by designing the capping layer material with specific functional regions: the benzofuran/benzothiophene core provides high refractive index for light extraction, while the amine groups and conjugated systems are positioned to provide optical transparency in the blue-green region. This spatial separation of functions within the molecule resolves the contradiction between refractive index and wavelength-specific absorption

Inventive Principle:

Principle #3Local quality

3Illumination intensity

If inorganic materials are used for capping layer to achieve high refractive index, then light extraction improves, but manufacturing complexity increases due to deposition requirements and heat distortion

Engineering Contradiction:

Improvelight extraction efficiencyVSAvoiddeposition precision and alignment accuracy

Core Design Contradiction:

Illumination intensityVSEase of manufacture

Solution Approach 1:

The patent substitutes the mechanical deposition process (sputtering, evaporation) required for inorganic materials with a solution-based or vapor-phase organic deposition process. This allows the capping layer to be formed using standard organic EL device fabrication techniques, eliminating the need for specialized inorganic deposition equipment and avoiding heat-induced mask distortion, thereby simplifying manufacturing while maintaining high refractive index properties

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 implementation of these amine compounds significantly improves light extraction efficiency and maintains color purity over time, resulting in a longer device lifetime and higher refractive index than traditional materials.

Implementation Method 1

when light emitted by a light emitting layer enters another layer at a certain angle or more, the light is totally reflected at an interface between the light emitting layer and the other layer

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

the maximum point of light extraction efficiency is determined by interference effects

Methodology Applied

Scientific EffectInterference effects: Interference

Data Source

PatentUS12622134B2Organic electroluminescent device, and electronic apparatus

Publication Date: 2026.05.05 HODOGAYA CHEMICAL CO LTD

AI summary

An object of the present invention is to provide a compound with a high refractive index and a low extinction coefficient at a wavelength in range of 450 nm to 750 nm in a capping layer to improve light extraction efficiency of an organic electroluminescent device. The present invention was achieved by focusing on the fact that a specific arylamine based compound has excellent thin film stability and durability and is able improve the refractive index by adjusting the molecular structures, and planning molecule, and an organic electroluminescent device having excellent luminous efficiency was obtained by using this compound as a material for constituting a capping layer.