White OLED Emission Area Uniformity via Layer Positioning
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Solution Overview
Problem
Conventional top emission type white organic light emitting devices suffer from inefficiency and color characteristic changes over time due to differing light emission efficiencies, leading to short lifespans and unreliable display performance.
Innovation Solution
A white organic light emitting device with a specific layered structure including a reflective electrode, transparent electrodes, blue and phosphorescent light emitting stacks, and charge generation layers, optimized with precise distance ratios and material compositions to ensure uniform light emission and extended lifespan, featuring a light compensation layer for improved out-coupling and color reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a top emission type white organic light emitting device is used to increase emission area, then the emission area is increased, but the device exhibits insufficient efficiency and color characteristics change over time due to different efficiencies of colors of light
Solution Approach 1:
The patent applies local quality by positioning blue light emitting layers at specific distances from the reflective electrode (first blue light emitting layer at 1000-2000 Å, second blue light emitting layer at 3000-5000 Å) to optimize light extraction efficiency for different colors. This localized structural optimization ensures that each light emitting layer operates at its optimal position, maintaining uniform efficiency across all colors and preventing color characteristic changes over time.
2Duration of action of stationary object
If conventional top emission type white organic light emitting devices are driven for a long time, then continuous operation is achieved, but specific colors of light have short lifespans and the device becomes unreliable
Solution Approach 1:
The patent employs parameter changes by optimizing the distances of blue light emitting layers from the reflective electrode (first blue light emitting layer: 1000-2000 Å, second blue light emitting layer: 3000-5000 Å) to enhance light extraction efficiency. This parameter optimization ensures uniform efficiency across all colors (red, green, blue), preventing any specific color from degrading prematurely and thereby extending the overall device lifespan for continuous operation.
3Illumination intensity
If a tandem-type white organic light emitting device is constructed with multiple light emitting layers, then white light is produced through combination of different colors, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the white light emitting device into distinct functional stacks: a first stack containing a blue light emitting layer and a second stack containing red and green light emitting layers. These segmented stacks are positioned at optimized distances from the reflective electrode, allowing independent optimization of each color component while maintaining overall device manageability and simplifying the fabrication process.
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 enhances the emission area and stability of white light output across colors, maintaining uniform lifespans and color characteristics even after prolonged use, thereby improving the reliability and performance of the display device.
Implementation Method 1
a reflective electrode, a first transparent electrode on the reflective electrode
Implementation Method 2
a phosphorescent stack on the first blue stack, the phosphorescent stack including a third common layer, a phosphorescent light emitting layer
Data Source
AI summary
A white organic light emitting device and an organic light emitting display device using the white organic light emitting device stably implement white light in a tandem-type top emission structure through uniform lifespans according to emitted colors of light despite driving of the white organic light emitting device for a long time.