Organic Electroluminescent Device Light Extraction Layer Design
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Solution Overview
Problem
Organic electroluminescent devices suffer from low light extraction efficiency due to total reflection at the interface between the organic electroluminescent layer and air, with existing solutions like fine particle layers having refractive index mismatches and inferior reflective electrodes, leading to suboptimal performance in light emission.
Innovation Solution
An organic electroluminescent device design featuring a reflective electrode made of Ag, a fine particle layer with a polymer refractive index equal to or greater than the organic electroluminescent layer, and a transparent substrate with a lower refractive index, optimized to minimize reflection and enhance light extraction efficiency by adjusting the ratio of non-light-emitting to light-emitting regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fine particle layer with polymer refractive index 0.9 times that of the organic electroluminescent layer is used, then the device structure is simple, but light extraction efficiency is poor because about 15% of light cannot enter the fine particle layer due to refractive index mismatch
Solution Approach 1:
The patent changes the refractive index parameter of the polymer material in the fine particle layer from 0.9 times to equal to or greater than the organic electroluminescent layer. This parameter change eliminates the refractive index mismatch barrier, allowing light to enter the fine particle layer efficiently while maintaining structural simplicity.
Solution Approach 2:
The patent uses composite materials consisting of polymer and fine particles to create a light extraction layer with optimized optical properties. The composite structure provides both the refractive index matching capability and the light scattering function needed for efficient light extraction.
2Device complexity
If a reflective electrode of MgAg is used, then the device structure is simple, but light extraction efficiency is reduced because MgAg has inferior reflectivity compared to Ag, causing back-scattered light to be lost
Solution Approach 1:
The patent changes the material parameter of the reflective electrode from MgAg alloy to pure Ag. This material substitution significantly improves reflectivity, allowing back-scattered light to be effectively reflected back into the organic electroluminescent layer for a second extraction opportunity, thereby reducing energy loss.
3Illumination intensity
If the organic electroluminescent layer has high refractive index (1.7-1.85), then the light emission intensity is high, but light extraction efficiency is poor because about 70% of light is confined in the interior due to total reflection at the interface with air
Solution Approach 1:
The patent introduces a fine particle layer as an intermediary between the high refractive index organic electroluminescent layer and the air. This intermediate layer with matching or higher refractive index allows light to pass from the electroluminescent layer into the fine particle layer without total reflection, and the fine particles scatter the light to enable extraction at multiple angles.
Solution Approach 2:
The patent changes the refractive index parameter of the light extraction layer to be equal to or greater than the organic electroluminescent layer. This parameter change reverses the usual refractive index gradient, eliminating the total reflection barrier and enabling efficient light extraction while preserving the high emission intensity of the electroluminescent 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
Significantly improves light extraction efficiency, reducing power consumption and extending the device's service life by effectively preventing total reflection and maximizing light emission to the air.
Implementation Method 1
light emitted from an organic electroluminescent layer is scattered by the fine particle layer
Implementation Method 2
the reflective electrode of MgAg is inferior to a reflective electrode of Ag in terms of reflectivity
Implementation Method 3
the distribution of light emitted from the organic electroluminescent layer is a Lambertian distribution
Implementation Method 4
when light is emitted at an angle equal to or higher than a critical angle determined based on the refractive index of the organic electroluminescent layer and the refractive index of a medium into which the light is to be emitted, the light cannot be emitted to the air, totally reflected, and confined in the interior
Data Source
AI summary
Provided is an organic electroluminescent device including, in an order mentioned: a reflective electrode; an organic electroluminescent layer; a light extraction layer; and a transparent substrate, wherein a ratio (w/d) is 9 or more where “d” denotes a total average thickness from the organic electroluminescent layer to the transparent substrate and “w” denotes a minimum width of a non-light-emitting region present outside of an outer periphery of an effective light-emitting region in the organic electroluminescent layer.