Dual-Layer Arylamine Capping Layer for Organic EL Light Extraction
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Solution Overview
Problem
Existing organic electroluminescent (EL) elements with top emission structures face limitations in light extraction efficiency due to the use of capping layers, which can suffer from thermal deformation and damage when using inorganic materials, and result in decreased color purity and efficiency for blue light emitting elements.
Innovation Solution
The use of a capping layer structure comprising a first capping layer with a high refractive index and excellent stability, and a second capping layer with an even higher refractive index, both made from arylamine compounds, to improve light extraction efficiency while maintaining color purity and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a capping layer with high refractive index is used to improve light extraction efficiency, then light extraction efficiency is improved, but thermal deformation and damage occur at high temperatures
Solution Approach 1:
The capping layer is divided into multiple sub-layers with different organic compounds, each having different refractive indices. This segmentation allows the structure to achieve high light extraction efficiency through refractive index optimization while maintaining thermal stability by using organic materials that can be deposited at lower temperatures compared to inorganic materials.
Solution Approach 2:
The patent changes the refractive index parameter by selecting organic compounds with different refractive indices for different capping layer sub-layers. By optimizing the refractive index distribution across the capping layer structure, high light extraction efficiency is achieved without requiring high-temperature processing that would compromise thermal stability.
2Loss of energy
If inorganic materials are used for capping layer, then light extraction efficiency is improved, but the light emitting element is damaged during film formation
Solution Approach 1:
The patent replaces inorganic materials with organic compounds for the capping layer. This substitution eliminates the need for high-temperature vapor deposition processes that damage the light emitting element, while still achieving high light extraction efficiency through optimized refractive index matching in the organic capping layer structure.
3Stability of the object's composition
If Alq3 is used for capping layer to adjust refractive index, then refractive index is adjusted, but color purity and light extraction efficiency deteriorate for blue light emitting elements
Solution Approach 1:
Instead of using a single organic compound like Alq3, the patent segments the capping layer into multiple sub-layers, each with different organic compounds having different refractive indices. This allows precise control of the overall refractive index while minimizing absorption in the blue wavelength region, thereby maintaining color purity and light extraction efficiency for blue light emitting elements.
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 significantly enhances light extraction efficiency, maintains color purity, and extends the lifespan of organic EL elements, making them suitable for full-color displays with clear and bright images.
Implementation Method 1
a capping layer with a high refractive index is provided on the outside of a translucent electrode with a low refractive index, in order to improve the light extraction efficiency
Implementation Method 2
when light that is emitted by a light emitting layer and incident on another layer is incident at a certain angle or more, the light is totally reflected at an interface between the light emitting layer and the other layer
Implementation Method 3
the second capping layer contains an arylamine compound represented by the general formula (1)... a refractive index of the second capping layer is higher than a refractive index of the first capping layer throughout a wavelength range from 450 to 650 nm
Data Source
Figure 1
AI summary
It is an object of the present invention to provide an organic EL element including a capping layer constituted by two layers consisting of a first capping layer and a second capping layer that has a refractive index that is higher than that of the first capping layer, in order to improve the light extraction efficiency compared with an organic EL element including a capping layer constituted by a single layer. The present invention provides an organic electroluminescent element at least including an anode, a hole transport layer, a light emitting layer, an electron transport layer, a cathode, and a capping layer arranged in this order, wherein the capping layer has a structure constituted by two layers consisting of a first capping layer and a second capping layer, a refractive index of the second capping layer is higher than a refractive index of the first capping layer throughout a wavelength range from 450 to 650 nm, and the second capping layer contains an arylamine compound having a specific structure.