OLED Light Extraction via Low Refractive Electrode Layer
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Solution Overview
Problem
Organic light-emitting display apparatuses have low light extraction efficiency due to the waveguide phenomenon of total reflection, limiting the emission of light to about 20% outside the device.
Innovation Solution
Incorporating a low refractive layer with a refractive index of 1.4 or less in at least one of the reflective electrodes, along with a transparent electrode layer and a reflective layer, to minimize light absorption and enhance light extraction by controlling the critical angle and reducing repeated reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional reflective electrode structure is used, then the device structure is simple, but the light extraction efficiency is low due to waveguide phenomenon and total reflection
Solution Approach 1:
A low refractive index layer (refractive index ≤1.4) is introduced as an intermediary between the organic light-emitting layer and the reflective layer. This intermediary layer modifies the optical path by reducing the refractive index contrast, thereby minimizing total internal reflection and waveguide effects that trap light within the device. The low refractive index layer acts as an optical mediator that enables more efficient light extraction while maintaining structural simplicity.
Solution Approach 2:
The refractive index parameter of the electrode structure is deliberately changed by incorporating materials with refractive index ≤1.4 (such as ITO, ZnO, or SiO2) in the low refractive index layer. This parameter change optimizes the critical angle for light extraction and reduces the waveguide phenomenon, thereby improving light extraction efficiency from the traditional ~20% to significantly higher levels without complicating the overall device structure.
2Illumination intensity
If the refractive index of the electrode layer is high, then the reflective layer can effectively reflect light, but light is repeatedly reflected and confined within the device reducing extraction efficiency
Solution Approach 1:
The electrode structure is divided into regions with different refractive index properties: a low refractive index layer (≤1.4) positioned at the light emission interface to minimize total internal reflection, and a high refractive index reflective layer positioned deeper to provide effective light reflection. This local differentiation of optical properties allows each layer to perform its specific function optimally - the low refractive index layer extracts light efficiently while the reflective layer maintains its reflection capability.
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 significantly increases light extraction efficiency by reducing light absorption and improving the emission of light to the outside, as demonstrated by simulation results showing a higher luminous flux density and increased light output compared to traditional designs without the low refractive layer.
Implementation Method 1
at least one of the first and second reflective electrodes comprises a low refractive layer having a refractive index of about 1.4 or less
Implementation Method 2
light extraction efficiency is very low, and is known as about 20%. This is caused by a waveguide phenomenon based on total reflection
Data Source
AI summary
Disclosed is an organic light-emitting display apparatus. The organic light-emitting display apparatus includes a substrate, a first reflective electrode that is disposed over the substrate, an organic layer that is disposed over the first reflective electrode, and includes a light emission layer, and a second reflective electrode that is disposed over the organic layer. At least one of the first and second reflective electrodes comprises a low refractive layer having a refractive index of about 1.4 or less which is smaller than that of the organic layer.