OLED Light Extraction Substrate Flatness via Metal Oxide Matrix
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Solution Overview
Problem
The existing methods for increasing light extraction efficiency in organic light-emitting devices (OLEDs) face challenges such as light trapping due to refractive index differences between the glass substrate and the organic light-emitting layer, leading to only 20% of generated light being emitted externally, and the use of microlens arrays is prone to damage and increased surface roughness, which affects the longevity of the OLED.
Innovation Solution
A method involving the mixing of first and second metal oxide particles with an organic solvent, followed by heat-treatment and a second coating step, to form a metal oxide thin film where the first metal oxide particles are impregnated in a matrix of the second metal oxide, enhancing dispersibility and preventing bilayer formation, thereby increasing the flatness and light extraction efficiency of the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a microlens array is used to increase external light extraction efficiency, then light extraction efficiency is improved, but the light extraction layer becomes easily damaged and contaminated due to protruding convex-concave portions
Solution Approach 1:
The patent applies spherical microlens structures on the outer surface of the light extraction layer to increase external light extraction efficiency. The convex-concave portions are formed with controlled curvature radii (e.g., 5-50 μm for the microlens, and specific depth ratios) to optimize light extraction while managing the protrusion issue. This curvature-based approach allows light to be extracted more efficiently by refracting it at multiple angles, but the protruding lenses remain vulnerable to damage and contamination as noted in the problem statement.
Solution Approach 2:
The light extraction layer is segmented into multiple functional zones: an internal light extraction layer with convex-concave portions facing the organic light-emitting layer, and an external light extraction layer with microlens arrays facing outward. This segmentation allows each layer to perform its specific function - the internal layer extracts light from the waveguide mode, while the external layer further extracts light to the ambient, thereby improving overall light extraction efficiency while distributing the structural complexity across separate layers.
2Loss of energy
If the convex-concave structure is formed on the light extraction layer to increase internal light extraction, then internal light extraction efficiency is improved, but the anode develops localized sharp portions causing concentrated current and leakage
Solution Approach 1:
The patent applies local quality by creating convex-concave portions only on the internal light extraction layer that faces the organic light-emitting layer, while keeping the outer surface of the external light extraction layer relatively flat or separately structured with microlenses. This localized structuring allows internal light extraction to be enhanced at the interface with the organic layer without necessarily creating harmful sharp portions on the anode, as the external light extraction layer serves as a protective and smoothing interface.
Solution Approach 2:
The external light extraction layer acts as an intermediary between the internal light extraction layer and the anode. It mediates the optical extraction function while providing a protective barrier that prevents direct contact between the sharp convex-concave portions and the anode, thereby reducing the risk of current concentration and leakage. The external layer distributes mechanical and electrical stresses more evenly across the structure.
3Loss of energy
If light scattering particles are impregnated in a matrix material to increase light extraction, then light extraction efficiency is improved, but the surface roughness increases affecting OLED longevity
Solution Approach 1:
The patent utilizes a matrix material (such as resin or polymer) that can be impregnated with light scattering particles to form the light extraction layers. The matrix provides a continuous phase that binds the particles together, creating a porous or composite structure that enhances light scattering and extraction efficiency. The particles are distributed within the matrix to increase the refractive index contrast and scatter light effectively, while the matrix itself provides structural integrity and surface smoothing capabilities.
Solution Approach 2:
The light extraction layers are constructed as composite materials combining a matrix material (e.g., resin, polymer, or glass) with light scattering particles (e.g., TiO2, SiO2, ZrO2). This composite structure allows the material to simultaneously provide mechanical support, optical scattering properties, and surface flatness control. The matrix material fills the gaps between particles and provides a smooth outer surface, while the particles dispersed within enhance light extraction through scattering and refraction.
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 approach improves the light extraction efficiency by up to 55% and reduces leakage current, allowing the OLED to operate at lower currents, thus increasing its longevity and enabling the substrate to function as both an external and internal light extraction layer.
Implementation Method 1
mixing of first and second metal oxide particles with an organic solvent, enhancing dispersibility
Implementation Method 2
heat-treating and a second coating step, to form a metal oxide thin film
Implementation Method 3
particles of the first metal oxide are impregnated in a matrix of the second metal oxide
Implementation Method 4
coating a base substrate with a mixture of the first and second metal oxides and the organic solvent
Data Source
AI summary
A method of fabricating a light extraction substrate for an OLE) by which the flatness of the light extraction substrate for an OLED can be increased. Particles of a first metal oxide and a sol of a second metal oxide are inputted and mixed into an organic solvent. A base substrate is coated with a mixture of the first and second metal oxides and the organic solvent. A resultant coating film on the base substrate is heat-treated. The coating film is coated with the second metal oxide to form a metal oxide thin film on the base substrate. In the metal oxide thin film, the particles of the first metal oxide are impregnated in a matrix of the second metal oxide.