Reflective Electrode Surface Structure for OLED Light Extraction
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Solution Overview
Problem
In OLED and QLED display devices, the light extraction efficiency to the outside is low due to light absorption by the reflective electrode on the organic insulating film, caused by propagation of light through the substrate, evanescent waves, and surface plasmons.
Innovation Solution
A light-emitting element with a reflective electrode having a first protruding portion on its surface, where the height difference between the highest and lowest points of the protruding portion is between 0.4 μm and 1 μm, is used. This structure is formed by collectively baking the insulating film and the reflective electrode under vacuum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If photolithography is used to form periodic irregularities on the electrode surface, then light extraction efficiency is improved, but device complexity and manufacturing complexity increase due to requiring dedicated masks, optical exposure processes, and cleaning processes
Solution Approach 1:
The patent replaces the photolithography process (optical/mechanical system requiring masks and exposure equipment) with a self-organizing chemical process. The periodic irregularities form automatically through chemical reactions and self-assembly mechanisms during the manufacturing process, eliminating the need for complex photolithography equipment and procedures while achieving the same light extraction efficiency improvement.
Solution Approach 2:
The manufacturing process utilizes self-organizing mechanisms where the periodic irregularities on the electrode surface form automatically through chemical reactions and self-assembly. The system serves itself by creating the required structural features without external intervention from complex photolithography processes, thereby simplifying manufacturing while maintaining the light extraction efficiency benefits.
2Ease of manufacture
If a flat reflective electrode is used, then manufacturing is simpler, but light extraction efficiency remains low due to light absorption by the electrode on the organic insulating film
Solution Approach 1:
The patent applies local quality by creating periodic irregularities at specific locations on the reflective electrode surface. Instead of making the entire electrode complex, only localized periodic structures are formed, which are sufficient to improve light extraction efficiency while maintaining the overall simplicity of the electrode fabrication process.
Solution Approach 2:
The patent changes the surface topology parameter of the reflective electrode from flat to periodically irregular. This parameter change in surface morphology modifies the optical interaction between the electrode and light, improving light extraction efficiency by reducing light absorption through the organic insulating film while maintaining manufacturing simplicity through self-organizing formation mechanisms.
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 proposed solution significantly enhances the light extraction efficiency to the outside, achieving a higher efficiency compared to conventional methods without the need for complex photolithography processes.
Implementation Method 1
forming a protruding portion having a height in a range from 0.4 μm to 1 μm at least on a surface of the reflective electrode on the opposite side to the insulating film by collectively baking the insulating film and the reflective electrode under vacuum
Data Source
AI summary
A difference between the height of a highest point of a first protruding portion and the height of a lowest point of the first protruding portion in a film thickness direction of a reflective electrode is in a range from 0.4 μm to 1 μm.