OLED Pixel Defining Layer Pores for Light Extraction
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Solution Overview
Problem
Current organic light emitting diode (OLED) displays have a low light extraction efficiency, with only about 20% of the light generated from the light emitting layer being emitted outside, while the remaining 80% is confined or absorbed within the structure, resulting in reduced luminance and efficiency.
Innovation Solution
The formation of pores in the pixel defining layer using a light transmissive insulating polymer, such as polyimide, scatters light that would otherwise be lost to the side, redirecting it towards the light emitting surface, thereby enhancing light extraction efficiency without the need for additional scattering agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If light is emitted from the light emitting layer, then light generation occurs, but most light (about 80%) is confined and extinguished within the OLED structure rather than being emitted outside
Solution Approach 1:
The pixel defining layer is designed with a porous structure containing multiple pores. This porous structure scatters light that would otherwise be confined and extinguished, redirecting it toward the light emitting surface. The pores are formed by dissolving a sacrificial material (such as a surfactant) from the pixel defining layer, creating a three-dimensional porous network that enhances light extraction efficiency without adding complex external scattering components.
2Loss of energy
If pores are formed in the pixel defining layer to scatter light, then light extraction efficiency is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The pixel defining layer material itself serves dual functions: it defines pixel boundaries and simultaneously acts as a light scattering medium through its porous structure. The pores are created by incorporating and subsequently removing a sacrificial material (such as a surfactant) that is already part of the pixel defining layer composition. This self-service approach integrates the scattering function into the existing pixel defining layer without requiring separate scattering components or complex multi-step structuring processes.
Solution Approach 2:
The optical parameters of the pixel defining layer are modified by changing its physical structure from dense to porous. By controlling the pore size, pore distribution, and porosity ratio (volume of pores to total volume), the light scattering properties are optimized. The pore diameter is controlled to be within a specific range (e.g., 10-200 nm) to effectively scatter visible light while maintaining the electrical insulation and structural integrity of the pixel defining layer.
3Loss of energy
If additional scattering agents or layers are added to improve light extraction, then light efficiency increases, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The light scattering function is merged with the pixel defining layer, eliminating the need for separate scattering agents or scattering layers. The pixel defining layer is formulated to contain a sacrificial material (such as a surfactant) that, when removed, creates pores providing the scattering effect. This merging of functions reduces the total number of layers and materials required, simplifying the manufacturing process while achieving enhanced light extraction efficiency.
Solution Approach 2:
The sacrificial material (such as a surfactant) is selectively extracted or dissolved from the pixel defining layer after the layer is formed. This extraction process creates the porous structure in situ, removing the need to incorporate complex scattering agents during the initial layer formation. The sacrificial material is taken out through dissolution in a suitable solvent, leaving behind a porous network that provides light scattering while maintaining the structural and electrical functions of the pixel defining layer.
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 increases light efficiency by scattering and emitting the previously lost light, resulting in improved luminance and a simpler structure for the OLED display.
Implementation Method 1
forming pores in a pixel defining layer such that light incident on the pixel defining layer is scattered and emitted toward a light emitting surface
Data Source
AI summary
An organic light emitting diode display includes a substrate, first electrodes patterned on the substrate, pixel defining layers on the substrate to separate the first electrodes corresponding to pixel units, light emitting layers on the first electrodes and separated corresponding to the pixel units, and a second electrode on the light emitting layers, wherein the pixel defining layers have pores.