Light Extraction Efficiency via Fine Particle Texturing on Electrodes
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Solution Overview
Problem
The efficiency of light extraction from electroluminescent elements is limited due to total reflection at interfaces with different refractive indices, leading to low power efficiency in displays, as only about 20% of emitted light is extracted, with the remaining light being absorbed or reflected.
Innovation Solution
Incorporating fine particles with a refractive index equal to or higher than the second electrode on the light extraction side, which changes the surface shape of the electrode, allowing light that would normally be totally reflected to be refracted and extracted, thereby reducing total reflection and improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional smooth electrode surface is used, then the device structure is simple, but light extraction efficiency is low due to total reflection at interfaces
Solution Approach 1:
The patent applies by covering the electrode surface with fine particles, transforming the smooth planar surface into a curved, textured surface. This curvature modification changes the critical angle for total internal reflection, allowing more light to escape the device. The fine particles create multiple interfaces with different curvature radii, effectively reducing total reflection losses while maintaining structural simplicity.
Solution Approach 2:
The patent changes the surface parameter of the electrode by introducing fine particles with specific refractive indices (equal to or higher than the electrode). This parameter change in surface refractive index distribution modifies the optical properties at the interface, reducing total internal reflection and improving light extraction efficiency without fundamentally changing the electrode's basic structure.
2Loss of energy
If fine particles with high refractive index are introduced to improve light extraction, then light extraction efficiency increases, but device complexity increases
Solution Approach 1:
The patent uses fine particles as an intermediary layer between the electrode and the external environment. These particles serve as a mediator that modifies optical properties without requiring fundamental changes to the electrode structure. The intermediary particles with high refractive index create favorable optical conditions for light extraction while keeping the overall device structure relatively simple and manageable.
3Illumination intensity
If more light is extracted from the light emitting layer, then display brightness improves, but power consumption increases due to total reflection losses
Solution Approach 1:
The patent converts the harmful effect of total internal reflection (which causes light loss and reduced brightness) into a beneficial effect. By introducing fine particles with high refractive index, the patent transforms the optical conditions at the interface so that previously trapped light can now escape. This converts the harmful reflection loss into useful light output, improving brightness without proportionally increasing power consumption.
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 approach significantly enhances light extraction efficiency, reducing power consumption and improving display brightness and image quality, particularly in top emission structures.
Implementation Method 1
by providing a film having dispersed particles over a transparent conductive film to scatter the emitted light, the population of the light, which passes the interface between the transparent conductive film and a low refractive index film, with an incidence angle larger than the critical angle
Implementation Method 2
The first electrode of the abovementioned light emitting element is an electrode which can reflect light emitted from the light emitting layer
Implementation Method 3
the second electrode is an electrode which can transmit light emitted from the light emitting layer
Data Source
AI summary
A method to improve light extraction efficiency of a light emitting element such as an electroluminescent element is disclosed. Over a substrate, a first electrode, a light emitting layer, and a second electrode are sequentially stacked. The first electrode is a reflective electrode. The second electrode is an electrode which transmits visible light, and light emitted from the light emitting layer is extracted from the second electrode. In contact with a surface of the second electrode, many fine particles are provided. The fine particles have a refractive index which is equal to or higher than that of the second electrode. Light which passes through the second electrode is scattered and refracted by the fine particles. Accordingly, the amount of light which is totally reflected at an interface between the second electrode and a gas is reduced, and light extraction efficiency is improved.