OLED Light Extraction via Refractive Index Layering
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Solution Overview
Problem
Organic light-emitting devices (OLEDs) face challenges with low light extraction efficiency, which affects their emission efficiency and overall performance, particularly when trying to achieve full-color displays with multiple subpixels requiring different emission colors.
Innovation Solution
The proposed solution involves a light-emitting apparatus structure where a common layer with a high refractive index is used between the reflective electrode and the light-emitting layer for subpixels emitting shorter wavelengths, and an additional low refractive index layer is introduced for subpixels emitting longer wavelengths, optimizing the optical path length and refractive indices to enhance light extraction efficiency across all colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single layer structure is used between the reflective electrode and the light-emitting layer, then the device structure is simple, but the light extraction efficiency is insufficient for multiple emission colors
Solution Approach 1:
The patent applies local quality by introducing a second layer with different refractive index properties specifically for light-emitting layers emitting longer wavelengths. This allows different regions of the device to have optimized optical properties tailored to their specific emission characteristics, improving light extraction efficiency for red and green subpixels without compromising the simplicity of blue subpixel structure
Solution Approach 2:
The patent changes the refractive index parameter by introducing a second layer with a refractive index that is 0.15 or more lower than the first layer. This parameter modification enables optimization of light extraction efficiency for specific wavelength ranges while maintaining overall device functionality and structure
2Loss of energy
If different layer structures are used for each emission color, then the light extraction efficiency is optimized for each color, but the manufacturing complexity increases
Solution Approach 1:
The first layer structure serves multiple functions: it is used in all emission color subpixels (blue, green, red) and also serves as the base structure for the second layer in green and red subpixels. This multi-functional design allows optimization of light extraction efficiency for multiple colors while avoiding the need for completely separate structures for each emission color
Solution Approach 2:
The patent segments the optical adjustment function into two parts: a common first layer that provides basic optical optimization for all colors, and a selective second layer that provides additional optimization for specific wavelength ranges. This segmentation allows the device to achieve color-specific optimization without requiring entirely separate structures for each subpixel type
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 improves light extraction efficiency and emission efficiency for multiple emission colors, allowing for high-efficiency, cost-effective, and simplified manufacturing of OLEDs with improved color purity and reduced power consumption.
Implementation Method 1
Carriers are injected by application of voltage to the device, and recombination energy of the carriers is used, whereby light emission can be obtained from the light-emitting substance
Implementation Method 2
An ordinary refractive index of the second layer B is lower than an ordinary refractive index of the first layer A by a value greater than or equal to 0.15, with respect to the emission peak wavelength of the light-emitting substance B
Data Source
AI summary
A light-emitting apparatus with high emission efficiency is provided. A light-emitting apparatus including a light-emitting device A and a light-emitting device B is provided. The light-emitting device A includes a first electrode A, a second electrode A, a light-emitting layer A interposed between the first electrode A and the second electrode A, and a first layer A interposed between the first electrode A and the light-emitting layer A. The light-emitting device B includes a first electrode B, a second electrode B, a light-emitting layer B interposed between the first electrode B and the second electrode B, a first layer B interposed between the first electrode B and the light-emitting layer B, and a second layer B interposed between the first electrode B and the light-emitting layer B. The light-emitting layer A contains a light-emitting substance A. The light-emitting layer B contains a light-emitting substance B. An emission peak wavelength of the light-emitting substance A is shorter than an emission peak wavelength of the light-emitting substance B. The first layer A and the first layer B contain the same material. An ordinary refractive index of the second layer B is lower than an ordinary refractive index of the first layer A by a value 0.15 or more, with respect to the emission peak wavelength of the light-emitting substance B.