OLED Capping Layer Surface Roughness for Reflection Control
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Solution Overview
Problem
Organic light emitting diode (OLED) displays face reduced image visibility and quality due to ambient light reflection and the formation of Newton's rings caused by differences in refractive indexes between thin films and substrates, leading to decreased contrast and black levels.
Innovation Solution
An OLED display structure incorporating a capping layer with higher surface roughness, made from crystallized organic or inorganic materials, and spacers with specific shapes to disperse ambient light and minimize the formation of Newton's rings, thereby improving visibility and reducing thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional smooth capping layer is used, then the manufacturing process is simple, but ambient light reflection occurs and Newton's rings are formed, reducing image visibility
Solution Approach 1:
The capping layer is designed with non-uniform surface roughness: the first region (over pixel electrodes) has higher surface roughness to scatter ambient light and suppress Newton's rings, while the second region (over pixel defining layer) maintains lower surface roughness for manufacturing simplicity. This local differentiation resolves the contradiction between manufacturing ease and reflection suppression.
Solution Approach 2:
The capping layer acts as an intermediary element between the organic emission layer and the external environment. By controlling its surface roughness in different regions, it mediates the interaction between ambient light and the display structure, scattering harmful reflections while maintaining manufacturing feasibility.
2Object-affected harmful factors
If the capping layer surface roughness is increased to suppress reflection, then ambient light reflection is reduced, but the manufacturing complexity increases
Solution Approach 1:
Instead of uniformly increasing surface roughness across the entire capping layer, the invention applies high surface roughness only to the first region over the pixel electrodes where reflection suppression is most critical. The second region over the pixel defining layer maintains lower roughness, simplifying the overall manufacturing process while achieving the necessary reflection suppression.
Solution Approach 2:
The invention applies surface roughness enhancement partially rather than excessively across the entire capping layer. By limiting the rough surface treatment to only the necessary first region, it achieves adequate reflection suppression without the full manufacturing complexity that would result from treating the entire layer.
3Object-affected harmful factors
If uniform surface roughness is applied across the capping layer, then ambient light reflection is suppressed, but the manufacturing precision requirements increase
Solution Approach 1:
The invention differentiates surface roughness requirements by region: the first region over pixel electrodes requires higher surface roughness to suppress Newton's rings and ambient light reflection, while the second region over the pixel defining layer requires lower surface roughness. This local quality differentiation reduces overall manufacturing precision requirements compared to enforcing uniform high roughness across the entire 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
The solution effectively suppresses ambient light reflection and Newton's ring formation, enhancing image quality and visibility while potentially eliminating the need for additional light suppression layers, thus improving luminous efficiency and lifespan.
Implementation Method 1
a capping layer formed on the common electrode, to cover the organic emission layer... The capping layer may have a higher surface roughness than a conventional non-crystallized capping layer... effectively suppresses ambient light reflection
Implementation Method 2
since an organic light emitting diode display includes a plurality of thin films and substrates, a concentric circle pattern (Newton's ring) may be generated, due to the films and substrates having different refractive indexes. The capping layer... suppresses the formation of a Newton's ring
Data Source
AI summary
An organic light emitting diode display including: a substrate; a plurality of pixel electrodes formed on the substrate; a pixel defining layer formed on the substrate, having openings exposing the pixel electrodes; a plurality of spacers disposed on the pixel defining layer; organic emission layers formed on the pixel electrodes; a common electrode formed on the organic emission layers; and a capping layer formed on the common electrode, to cover the organic emission layers.