White OLED Stack Structure with Energy Level Inversion
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Solution Overview
Problem
White organic light emitting devices face limitations in efficiency, lifespan, and power consumption due to the restrictive internal quantum efficiency of blue fluorescent layers, which affects color reproduction and stability.
Innovation Solution
A white organic light emitting device with a stack structure of blue fluorescence and red/green phosphorescence is developed, featuring a first stack with a blue light emitting layer and a second stack with red and green phosphor layers, where the energy levels of the hole transport layers are set higher than the triplet exciton energy levels to prevent exciton migration, and metal-doped electron transport layers enhance efficiency through triplet-triplet annihilation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a blue fluorescent layer is used in the white organic light emitting device, then the device can be fabricated with simpler processes, but the internal quantum efficiency is limited to 25% which reduces overall device efficiency
Solution Approach 1:
The patent changes the energy level parameters of the hole transport layer and electron transport layer to be higher than the triplet exciton energy level of the blue fluorescent layer. This parameter adjustment prevents triplet exciton migration to transport layers, enabling the blue fluorescent layer to achieve internal quantum efficiency exceeding 25% while maintaining fabrication simplicity.
2Reliability
If the energy level of hole transport layer is set lower than triplet exciton energy level, then exciton blocking is achieved, but triplet excitons migrate to the hole transport layer causing deteriorated light emitting efficiency
Solution Approach 1:
Instead of setting the hole transport layer energy level lower than the triplet exciton energy level (conventional approach), the patent inverts this relationship by setting the hole transport layer energy level higher. This inversion prevents triplet exciton migration to the hole transport layer while maintaining effective exciton blocking through the electron transport layer, thereby preserving light emitting efficiency.
3Adaptability or versatility
If dopants with different colors are mixed to obtain white light, then various colors can be produced, but a peak value occurs at a wavelength other than red, green and blue causing deteriorated color reproduction rate
Solution Approach 1:
The patent segments the white light generation into distinct red and green phosphorescence layers plus a blue fluorescent layer, rather than using a single mixed dopant layer. This segmentation prevents unwanted peak formation and ensures that the emitted light contains only the desired red, green, and blue wavelengths, thereby improving color reproduction rate while maintaining color production capability.
4Productivity
If an exciton blocking layer is provided to prevent triplet exciton migration, then light emitting efficiency is improved, but driving voltages and process steps are increased and lifespan is reduced
Solution Approach 1:
The patent makes the electron transport layer and hole transport layer serve dual functions: they transport their respective charge carriers and simultaneously block triplet excitons through their elevated energy levels. This multi-functionality eliminates the need for a separate exciton blocking layer, reducing device complexity and process steps while maintaining improved light emitting efficiency.
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 the efficiency and lifespan of the blue fluorescent layer, enhances color quality, and reduces power consumption, achieving a theoretical internal quantum efficiency of 37.6% and doubling the lifespan while maintaining cool white color properties.
Implementation Method 1
a blue fluorescent layer of a singlet exciton is used
Implementation Method 2
red/green phosphorescence
Implementation Method 3
metal-doped electron transport layers enhance efficiency through triplet-triplet annihilation
Data Source
AI summary
A white organic light emitting device having a stack structure of blue fluorescence and red/green phosphorescence is disclosed, in which efficiency of the blue fluorescence is improved to increase lifespan of the white organic light emitting device, color quality is improved, and power consumption is reduced.