OLED Capping Layer Material for Light Extraction and Color Purity
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Solution Overview
Problem
Conventional organic electroluminescent (EL) elements face issues with light extraction efficiency, color purity, and durability due to the use of capping layers that either distort under high temperatures or absorb harmful wavelengths, affecting the internal materials and reducing efficiency.
Innovation Solution
A capping layer composed of an arylamine-based material with a benzoazole ring structure is used, featuring high absorption coefficients, refractive index, stability, and durability, which absorbs harmful wavelengths without affecting internal elements and enhances light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metal mask is used for forming a capping layer under high temperature conditions, then alignment accuracy is maintained initially, but the metal mask distorts due to heat, causing deposition at inaccurate positions and affecting luminous element performance
Solution Approach 1:
The patent replaces the reusable metal mask with a disposable photoresist pattern that is formed on the substrate before deposition. This photoresist pattern serves as a temporary masking layer that defines the capping layer pattern, eliminating the need for high-temperature metal masks and their associated thermal distortion problems.
Solution Approach 2:
The patent replaces the mechanical metal mask system with a photochemical patterning system. Instead of using a physical metal mask that blocks deposition, the invention uses photolithography to create a photoresist pattern that is subsequently used as a mask, allowing for more precise pattern transfer without thermal distortion.
2Loss of energy
If Alq3 is used as a capping layer to adjust refractive index, then light extraction efficiency is improved, but color purity decreases due to weak absorption near 450 nm in blue luminous materials
Solution Approach 1:
The patent changes the material parameter of the capping layer from Alq3 to a compound with specific structural features (formula 1) that has appropriate optical properties. The new compound has a refractive index suitable for light extraction while lacking the problematic 450 nm absorption band, thus maintaining color purity for blue luminous materials.
Solution Approach 2:
The patent applies a capping layer with specific local optical properties - high refractive index for light extraction enhancement but without the harmful 450 nm absorption characteristic of Alq3. The compound of formula (1) provides localized improvement in light extraction efficiency without compromising color purity.
3Loss of energy
If a capping layer with high refractive index is added to improve light extraction efficiency, then light extraction efficiency increases, but device complexity increases due to additional layer deposition processes
Solution Approach 1:
The patent integrates the capping layer function into the existing device structure using a compound that serves multiple purposes: it provides the necessary high refractive index for light extraction enhancement while also offering thermal stability and chemical compatibility with other device layers. The compound of formula (1) acts as both a functional capping layer and a protective layer.
Solution Approach 2:
The patent combines the capping layer deposition with the existing vacuum deposition process used for other device layers. By using the same deposition equipment and process conditions, the capping layer is formed as part of the overall device fabrication sequence, minimizing additional process complexity.
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 new capping layer maintains color purity and significantly improves light extraction efficiency, ensuring high-definition displays with long-lasting performance.
Implementation Method 1
absorb light having a wavelength of 400 nm to 410 nm of sunlight so as not to affect the material inside the element
Implementation Method 2
a luminous element provided with a 'capping layer' with a high refractive index on the outside of a semitransparent electrode with a low refractive index has been proposed to improve light extraction efficiency
Data Source
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AI summary
The present invention is related to an organic EL element having a capping layer composed of a material having (1) a high absorption coefficient; (2) a high refractive index; (3) good stability of a thin film; (4) excellent durability; (5) excellent light resistance; and (6) no absorption in each of the wavelength regions of blue, green, and red. Since an arylamine-based material having a specific structure according to the present invention is excellent in the stability and durability of a thin film, an organic EL element in which an amine compound having a specific benzazole ring structure having a high refractive index is selected as a material having a high absorbance at a wavelength of 400 nm to 410 nm in an absorption spectrum having a concentration of 10-5 mol/L and used as a material constituting a capping layer exhibits good element characteristics.