Organic Electroluminescent Element Planarization Layer Stray Light
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Solution Overview
Problem
Higher-definition organic electroluminescent devices suffer from light bleeding and decreased color purity due to stray light caused by uneven protective layers, which current methods attempt to address by planarizing the protective layer but compromise film thickness and increase costs.
Innovation Solution
An organic electroluminescent element with a planarization layer having a refractive index equal to or lower than the protective layer and equal to or higher than the light emission medium, in contact with a protective layer having an uneven shape, to suppress stray light without compromising reliability or increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the protective layer is polished by the CMP method to reduce uneven shape, then light bleeding and color mixture are reduced, but the film thickness of the protective layer is decreased to decrease waterproof performance
Solution Approach 1:
The protective layer is divided into two functional layers: a first protective layer that maintains thickness and waterproof performance, and a second protective layer that is polished flat to reduce light bleeding. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
A planarization layer is introduced as an intermediary between the uneven first protective layer and the external environment. This planarization layer absorbs the surface unevenness while maintaining the underlying protective layer's thickness and waterproof properties, thereby preventing light bleeding without sacrificing reliability.
2Manufacturing precision
If a thick protective layer is formed in advance and then polished by CMP method, then surface flatness is improved to reduce stray light, but the formation time of the protective layer is increased to increase costs
Solution Approach 1:
The protective layer formation process is segmented into two steps: first forming a thick protective layer for waterproof protection, then forming a thin planarization layer for surface flatness. This avoids the need to form and polish a single thick protective layer, reducing overall formation time while maintaining both waterproof performance and surface quality.
Solution Approach 2:
The planarization layer is designed as a thin, disposable layer that provides surface flatness temporarily. Since it is thin and can be formed quickly, it reduces the overall time and cost compared to forming and polishing a thick protective layer, while still achieving the desired surface flatness for reducing light bleeding.
3Reliability
If the protective layer is made thick to maintain waterproof performance, then reliability is improved, but the uneven shape causes more stray light and light bleeding
Solution Approach 1:
The protective system is segmented into a thick first protective layer for waterproof performance and a thin second protective layer (planarization layer) for surface flatness. This allows the thick layer to maintain reliability while the thin polished layer prevents stray light and light bleeding.
Solution Approach 2:
The planarization layer acts as an intermediary that covers the uneven surface of the thick protective layer. It provides a flat outer surface that prevents light bleeding and stray light generation, while the underlying thick protective layer maintains waterproof performance and reliability.
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 reduces light bleeding and color mixture in light-emitting regions, maintaining reliability and controlling costs by minimizing reflection, scattering, and refraction from the protective layer's uneven shape.
Implementation Method 1
a refractive index of the planarization layer is equal to or lower than the refractive index of the protective layer and equal to or higher than the refractive index of a light emission medium
Implementation Method 2
The guided light propagates in the light-emitting device in a direction parallel to a substrate surface by reflection from a lower electrode, an insulating layer, an upper electrode, a protective layer
Implementation Method 3
When a structure that does not satisfy waveguide conditions is present, the guided light becomes stray light due to reflection, refraction, or scattering
Data Source
AI summary
An organic electroluminescent element includes a first electrode, a second electrode, and an organic compound layer disposed between the first and second electrodes. A protective layer and a planarization layer are disposed in this order on the light emission side of whichever of the first and second electrodes is closer to the light emission side. A surface of the protective layer adjacent to the planarization layer has an uneven shape. The planarization layer is in contact with the protective layer. A surface of the planarization layer away from the protective layer is flat. The refractive index of the planarization layer is equal to or lower than that of the protective layer and equal to or higher than that of a light emission medium in contact with the planarization layer.