White OLED TER-TEP Structure Host Material Optimization
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Solution Overview
Problem
Existing white organic light emitting diodes (OLEDs) face challenges in achieving high luminance and color reproduction ratio due to differences in emission efficiency between fluorescent and phosphorescent materials, leading to low emission efficiency and color reproduction ratios when combined with color filters.
Innovation Solution
A white OLED with a TER-TEP (Three Emission Region-Three Emission Peak) structure, featuring three emitting parts with specific peak wavelengths, is developed, where the blue emitting layer is closer to the cathode, and the red emitting layer includes host materials with different energy band gaps to enhance emission efficiency and luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a white OLED uses blue and yellow emitting layers with complementary colors, then white light emission is achieved, but the color reproduction ratio becomes small due to mismatch between peak wavelength regions and color filter transmission areas
Solution Approach 1:
The white OLED is divided into three separate emitting layers (blue, green, red) instead of using two layers with complementary colors. Each layer is responsible for emitting a specific color with a well-defined peak wavelength that matches the transmission characteristics of the color filters, thereby improving color reproduction ratio while maintaining white light emission.
Solution Approach 2:
Each emitting layer is optimized with specific host materials having appropriate energy band gaps to ensure that the peak emission wavelength of each layer precisely matches the transmission peak of its corresponding color filter. This local optimization of emission characteristics improves the overall color reproduction ratio.
2Illumination intensity
If the blue emitting layer uses fluorescent material and yellow emitting layer uses phosphorescent material, then white light emission is achieved, but emission efficiency and color reproduction ratio are lowered due to efficiency difference between the two materials
Solution Approach 1:
The patent changes the emission mechanism parameter from a combination of fluorescent and phosphorescent materials to three fluorescent materials with different emission wavelengths. This parameter change eliminates the efficiency difference problem between fluorescent and phosphorescent materials, as all three layers can be optimized to have high fluorescent emission efficiency, thereby improving overall emission efficiency and color reproduction ratio.
3Illumination intensity
If the blue wavelength region has lower transmittance through color filters compared to red or green regions, then white light emission is achieved, but emission efficiency is reduced
Solution Approach 1:
The blue emitting layer is specifically optimized with host materials having appropriate energy band gaps to ensure high emission intensity at the blue wavelength region. This local optimization compensates for the lower transmittance of blue light through color filters, maintaining high overall emission 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
The TER-TEP structure improves emission intensity and color reproduction ratio by optimizing the energy band gaps of host materials in the blue and red emitting layers, enhancing the overall performance of the white OLED and organic light emitting display devices.
Implementation Method 1
When the electron generated in the cathode and the hole generated in the anode are injected into the inside of the light emitting layer, exciton is produced by a combination of the electron and hole. Then, when the exciton falls to a ground state from an excited state, the organic light emitting display device emits a light.
Implementation Method 2
the red emitting layer includes host materials with different energy band gaps to enhance emission efficiency and luminance
Data Source
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AI summary
Disclosed is a white organic light emitting diode comprising first and second electrodes (100, 700), and an emitting part (600) between the first and second electrodes (100, 700), the emitting part (600) including a red emitting layer (631) and a blue emitting layer (632) adjacent to the red emitting layer (631), wherein the red emitting layer (631) includes a first host material which does not absorb a blue light emitted from the blue emitting layer (632), and an organic light emitting display device using the same.