OLED Light Emitting Layers Roll-Off Mitigation
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Solution Overview
Problem
Conventional white OLEDs experience a roll-off phenomenon at high current, leading to reduced light emission efficiency and panel efficiency due to triplet-triplet annihilation, resulting in decreased intensity of green and red wavelengths and a limited color reproduction range.
Innovation Solution
The use of organic light emitting display devices with at least two light emitting layers, each doped with a phosphorescent yellow-phosphorescent green dopant but with different hosts and dosages, optimized to adjust the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, and with specific thicknesses and refractive indices to enhance exciton generation and balance charge injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional white OLED with a single phosphorescent yellow-phosphorescent green light emitting layer is used, then the device structure is simple, but the light emission efficiency is reduced due to the roll-off phenomenon at high current
Solution Approach 1:
The single light emitting layer is divided into multiple light emitting layers, each with different host materials and dopant dosages. This segmentation allows each layer to operate at optimized current densities, preventing the roll-off phenomenon that occurs when a single layer handles the entire current load.
Solution Approach 2:
Different regions (layers) of the light emitting structure are given different properties through varying host materials and dopant concentrations. This creates local optimization where each layer contributes differently to the overall emission, with some layers emitting more at lower currents and others at higher currents, collectively eliminating the roll-off effect.
2Device complexity
If a conventional white OLED with a single phosphorescent yellow-phosphorescent green light emitting layer is used, then the device structure is simple, but the color reproduction range is limited due to small FWHM area
Solution Approach 1:
The emission spectrum is segmented across multiple layers, with each layer contributing to different portions of the spectrum. This allows the combined output to achieve a broader color reproduction range with enhanced FWHM area, as each layer can be optimized for specific wavelength regions.
Solution Approach 2:
Multiple host materials with different photoluminescence characteristics are combined in separate layers. This composite approach creates a synergistic effect where the overall emission spectrum is broader and more intense than what a single host material could provide, enhancing both FWHM area and color reproduction.
3Illumination intensity
If the dopant dosage is increased to enhance light emission intensity, then the light emission efficiency improves, but the roll-off phenomenon becomes more severe at high current
Solution Approach 1:
Different dopant dosages are applied in different layers based on their specific host materials and emission characteristics. This local optimization allows each layer to achieve high emission intensity at its optimal current density without contributing to the roll-off phenomenon, as the burden is distributed across layers with varying dopant concentrations.
Solution Approach 2:
The dopant dosage parameter is varied across different layers rather than being uniform. This parameter change allows each layer to operate at its optimal point, with lower dopant dosages in layers that handle higher currents and higher dopant dosages in layers that handle lower currents, collectively maintaining high efficiency across the full current range.
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 effectively reduces the roll-off phenomenon, increasing light emission efficiency and panel efficiency by optimizing the dosage and host materials in the light emitting layers, resulting in enhanced color reproduction and intensity across the green and red wavelength ranges.
Implementation Method 1
a phosphorescent yellow-phosphorescent green light emitting layer... yellow light emitted from the phosphorescent yellow-phosphorescent green light emitting layer
Implementation Method 2
an organic light emitting device capable of displaying an image through control of light emission of an organic light emitting layer
Data Source
AI summary
Disclosed is an organic light emitting display device with an enhanced light emission efficiency at high current and an enhancement in panel efficiency through prevention of a roll-off phenomenon. The organic light emitting display device includes first and second electrodes formed on a substrate facing each other. A hole injection layer, a hole transport layer, at least first and second light emitting layers, and an electron transport layer are sequentially stacked between the first and second electrodes. The first light emitting layer includes different hosts while being doped with the same dopant in different dosages. The first light emitting layer includes a first host and a second host, and the second light emitting layer includes the first host and a third host different from the second host. The first and second light emitting layers are doped with the same phosphorescent yellow-phosphorescent green dopant in the same dosage.