OLED Hole Injection Layer Doping for Roll-Off Reduction
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Solution Overview
Problem
Conventional organic light emitting display devices experience a roll-off phenomenon where luminous efficiency decreases as luminance increases, due to the use of fluorescent blue materials in emission layers.
Innovation Solution
The use of a hole injection layer doped with a hole transporting material, such as hexaazatriphenylene (HAT-CN), in organic light emitting display devices enhances hole mobility and injection characteristics, stabilizing charge balance and increasing luminous efficiency by forming excitons effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a fluorescent blue emission layer is used to produce white light, then the device can achieve white light emission, but luminous efficiency decreases as luminance increases (roll-off phenomenon)
Solution Approach 1:
The patent changes the chemical composition parameters of the hole injection layer by doping HAT-CN with specific ratios of hole transporting materials (TPD, TAPC, or mCP at 0.5% to less than 10% by volume). This parameter optimization improves hole mobility and injection characteristics, stabilizing charge balance across different luminance levels and reducing the roll-off phenomenon while maintaining white light emission capability
Solution Approach 2:
The patent creates a composite hole injection layer by combining HAT-CN (host material) with hole transporting materials (dopants) in specific ratios. This composite structure leverages the complementary properties of both materials: HAT-CN provides good hole injection capability while the dopant enhances hole mobility and charge transport, collectively improving luminous efficiency across various luminance regions
2Loss of energy
If the hole injection layer is doped with hole transporting material, then hole mobility and luminous efficiency are enhanced, but the device structure and manufacturing process become more complex
Solution Approach 1:
The patent merges the hole injection function and hole transport function into a single composite hole injection layer. By doping HAT-CN with hole transporting materials, the layer simultaneously performs both hole injection from the electrode and hole transport to the emission layer, simplifying the overall device structure compared to using separate layers while maintaining enhanced luminous efficiency
Solution Approach 2:
The composite hole injection layer serves multiple functions: it provides hole injection from the electrode, transports holes to the emission layer, and stabilizes charge balance across different luminance levels. This multi-functionality is achieved through the synergistic combination of HAT-CN and hole transporting materials in specific ratios, reducing the need for additional specialized layers
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 approach results in improved luminous efficiency and reduced roll-off phenomenon across various luminance regions, with enhanced peak intensity and reduced power consumption, particularly in blue and white light emission.
Implementation Method 1
a hole injection layer of a light emitting stack to realize blue color of the first and second light emitting stacks is formed by doping a host formed of hexaazatriphenylene (HAT-CN) with 0.5% to less than 10% of a dopant formed of a hole transporting material
Implementation Method 2
an organic light emitting display device includes first and second electrodes facing each other on a substrate, a charge generation layer formed between the first and second electrodes, a first light emitting stack formed between the charge generation layer and the first electrode
Data Source
AI summary
An organic light emitting display device includes first and second electrodes facing each other on a substrate, a charge generation layer formed between the first and second electrodes, a first light emitting stack formed between the charge generation layer and the first electrode, and a second light emitting stack formed between the charge generation layer and the second electrode, wherein a hole injection layer of a light emitting stack to realize blue color of the first and second light emitting stacks is formed by doping a host formed of hexaazatriphenylene (HAT-CN) with 0.5% to less than 10% of a dopant formed of a hole transporting material based on a volume of the hole injection layer.