OLED Outcoupling Body Refractive Index Matching
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Solution Overview
Problem
Existing organic light-emitting devices (OLEDs) face significant challenges in efficiently outcoupling light due to refractive index differences between substrate, electroluminescent layers, and the environment, leading to low light emission efficiency, with previous solutions either being complex and costly or offering limited improvements.
Innovation Solution
The introduction of an optical transparent outcoupling body with a high refractive index, placed on top of the substrate electrode, which covers part of the electroluminescent layer stack, enhances light outcoupling by minimizing reflective index transitions and using non-conductive glue for easy application and electrical isolation, allowing for improved light redirection and reduced absorption losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If light scattering layers are used to improve light outcoupling, then light outcoupling efficiency is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent introduces an optical element with a specific refractive index (1.7-1.9) as an intermediary layer between the substrate electrode and the electroluminescent layer stack. This intermediary optical element acts as a refractive index bridge, gradually transitioning light from the high-index substrate electrode to the lower-index environment, thereby improving light outcoupling efficiency without requiring complex scattering structures or additional manufacturing steps
Solution Approach 2:
The patent changes the refractive index parameter of the optical element to be specifically 1.7-1.9, which is intermediate between the substrate electrode (1.9-2.0) and the electroluminescent layer stack (1.7-1.9). This parameter optimization minimizes reflective losses at interfaces and improves light extraction efficiency while maintaining a simple device structure
2Loss of energy
If substrate recesses with reflective material are used to improve light outcoupling, then light outcoupling is improved, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of creating complex substrate recesses with reflective materials, the patent uses a planar optical element with a specifically optimized refractive index (1.7-1.9) as a mediator. This simplifies manufacturing by eliminating the need for substrate etching, recess formation, and reflective material deposition, while still achieving improved light outcoupling through refractive index matching
Solution Approach 2:
The patent optimizes the refractive index parameter of the optical element to match the electroluminescent layer stack (1.7-1.9), creating minimal optical impedance mismatch. This parameter optimization achieves effective light extraction without requiring complex substrate structuring or additional reflective layers, thereby simplifying the manufacturing process
3Device complexity
If conventional optical elements with mismatched refractive indices are used, then device structure is simple, but light outcoupling efficiency remains low due to reflective losses
Solution Approach 1:
The patent optimizes the refractive index parameter of the optical element to be specifically 1.7-1.9, which matches the electroluminescent layer stack. This parameter matching minimizes Fresnel reflections at the interface between the optical element and the electroluminescent layer, thereby significantly improving light outcoupling efficiency while maintaining a simple planar device structure without additional complexity
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 solution significantly increases light outcoupling efficiency by optimizing the refractive index matching and using non-conductive materials to prevent electrical field enhancements, resulting in a simpler and more cost-effective manufacturing process while maintaining high optical transparency and reduced absorption losses.
Implementation Method 1
The indices of refraction of the substrate electrode, the electroluminescent layer stack and of glass are typically 1.9 to 2.0, 1.7 to 1.9, and about 1.5, respectively. Due to the differences between the refractive indices of the substrate, the layers and the environment, usually air, most of the light generated in the OLED is not able to escape from the substrate to the outside.
Implementation Method 2
30% of the light is trapped in the light guide formed by the organic layers and the ITO
Implementation Method 3
The optical transparent body may be attached to the substrate electrode via thin adhesive means such as glue not disturbing the optical properties of the outcoupling body and the substrate electrode
Data Source
AI summary
The invention relates to an electroluminescent device (10) comprising a layer system with a substrate (40) and on top of the substrate (40) a substrate electrode (20), a counter electrode (30) and an electroluminescent layer stack with at least one organic electroluminescent layer (50) arranged between the substrate electrode (20) and the counter electrode (30), characterized in that at least one optical transparent outcoupling body (71) is provided on top of the substrate electrode (20) to increase the outcoupling of light generated by the at least one organic electroluminescent layer (50) at least partly covering the optical transparent outcoupling body (71). The invention further relates to a method to manufacture such a device.