OLED Capping Layer Refractive Index Light Extraction
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Solution Overview
Problem
Organic electroluminescent display devices suffer from low luminous efficacy due to significant light loss through total internal reflection, with only about ¼ of the light generated in the organic light emitting layer reaching the outside.
Innovation Solution
An organic light emitting display panel is designed with a front sealing layer comprising alternately laminated inorganic and organic barrier layers, and a capping layer with a higher refractive index than the inorganic barrier layer, along with an optional resonance inducing layer, to enhance light extraction through constructive interference and resonance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional organic light emitting display device is used, then the device structure is simple, but the luminous efficacy is low due to total internal reflection losing most light beams
Solution Approach 1:
The patent introduces a multi-layer sealing structure with alternating inorganic and organic barrier layers, adding dimensional complexity to the device architecture. This layered approach creates multiple interfaces that manipulate light propagation paths, enabling efficient light extraction while maintaining manufacturing feasibility through sequential deposition processes
Solution Approach 2:
The patent employs composite material structures combining inorganic barrier layers (such as silicon oxide, silicon nitride) with organic barrier layers. This composite approach leverages the complementary properties of both material types to achieve optimal light extraction efficiency while preventing degradation, resolving the contradiction between structural simplicity and energy loss
2Device complexity
If only a simple sealing layer is used, then the manufacturing process is simple, but light extraction efficiency is poor with only 1/4 light reaching outside
Solution Approach 1:
The patent segments the sealing layer into multiple alternating inorganic and organic barrier layers, with each layer serving specific functions. This segmentation creates numerous internal interfaces that facilitate light extraction through controlled reflection and refraction, transforming a single-layer simple structure into a multi-functional layered system that significantly improves light extraction efficiency
Solution Approach 2:
The patent introduces an intermediary capping layer with specific refractive index properties positioned between the sealing structure and the organic light emitting layer. This intermediary layer acts as an optical mediator that enhances light coupling and extraction efficiency, bridging the optical impedance mismatch between different materials while maintaining overall structural integrity
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 configuration increases light emission efficiency by up to 8-9% for blue light and improves color reproduction, effectively addressing the low luminous efficacy issue by efficiently redirecting and emitting light from the organic light emitting layer.
Implementation Method 1
All light beams generated in an organic light emitting layer of such an organic electroluminescent display device cannot reach the outside and most of the light beams are lost by total internal reflection
Implementation Method 2
enhance light extraction through constructive interference and resonance effects
Implementation Method 3
enhance light extraction through constructive interference and resonance effects
Implementation Method 4
emits light using energy generated by transition of excitons, which are generated when holes injected from an anode and electrons injected from a cathode recombine in a light emitting layer, from an excited state to a ground state
Data Source
AI summary
The organic light emitting display panel includes a first electrode formed on a substrate, an organic light emitting layer formed on the first electrode, a second electrode formed on the organic light emitting layer, a front sealing layer formed on the second electrode, wherein the front sealing layer is formed by alternately laminating an inorganic barrier layer and an organic barrier layer at least once, and at least one capping layer formed between the lowest layer closest to the second electrode among a plurality of thin films of the front sealing layer and the second electrode and having a higher index of refraction than an index of refraction of the lowest layer.