White OLED with Dopant-Adjusted Blue Layer for Color Stability
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Solution Overview
Problem
White organic light emitting devices face challenges in maintaining high color temperature and consistent color coordinates due to differing luminance change curves of blue fluorescent and red/green phosphorescent elements, leading to errors in color display, especially in low luminance regions.
Innovation Solution
A white organic light emitting device structure is implemented with a first stack having a blue fluorescent light emitting layer and a second stack with red and green phosphorescent light emitting layers, where the first stack's singlet-triplet exchange energy is adjusted, and dopant concentration is optimized to match the luminance change curve of the second stack, enhancing internal quantum efficiency and preventing carrier diffusion through higher triplet energy levels in transport layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blue fluorescent elements and red/green phosphorescent elements are stacked to produce white light, then the device achieves white light emission, but the color coordinates change due to different luminance change curves
Solution Approach 1:
The patent adjusts the dopant concentration in the blue fluorescent light emitting layer to match the luminance change curve of the red and green phosphorescent layers. By changing the dopant concentration parameter, the luminance characteristics of the blue layer are modified to compensate for the different emission characteristics of the phosphorescent layers, thereby maintaining stable color coordinates across the luminance range.
2Device complexity
If fluorescent elements are used in the light emitting layer, then the device structure is simplified, but the internal quantum efficiency is poor and red color is overemphasized
Solution Approach 1:
The patent optimizes the dopant concentration parameter in the blue fluorescent light emitting layer to achieve a balance between device simplicity and performance. By carefully controlling the dopant concentration, the internal quantum efficiency is improved while preventing excessive red color emission, thus maintaining both structural simplicity and emission quality.
3Manufacturing precision
If shadow mask is used for forming organic light emitting layer, then precise patterning is achieved, but the mask sags in large area applications and cannot be reused
Solution Approach 1:
The patent removes the shadow mask component from the deposition system. By using a maskless deposition technique, the mechanical constraints and sagging issues of large-area shadow masks are eliminated. This allows for direct deposition of organic materials without the need for physical masks, thereby improving both the precision and reusability aspects of the manufacturing 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
This configuration improves internal quantum efficiency to 25%-50%, maintains high color temperature, and stabilizes color coordinates across luminance changes without requiring additional algorithms, ensuring accurate white color representation.
Implementation Method 1
the first light emitting layer has low singlet-triplet exchange energy to change triplet excitons into a singlet state by triplet-triplet annihilation
Implementation Method 2
a first stack using blue fluorescent elements as a light emitting layer
Implementation Method 3
a second stack using red and green phosphorescent elements as a light emitting layer
Data Source
AI summary
A white organic light emitting device which has high color temperature characteristics and no change in color coordinates according to luminance change, includes a first electrode and a second electrode opposite to each other on a substrate, a charge generation layer formed between the first electrode and the second electrode, a second stack including a second light emitting layer formed between the charge generation layer and the second electrode, and a first stack including a first light emitting layer formed between the first electrode and the charge generation layer, wherein the first emitting layer has low singlet-triplet exchange energy to change triplet excitons into a singlet state by triplet-triplet annihilation and a dopant concentration of the first light emitting layer is adjusted according to a luminance change curve of the second stack.