OLED Emitting Layer Layout for Charge Balance and Durability
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Solution Overview
Problem
Existing organic light-emitting elements face challenges in improving light emission characteristics and driving durability, particularly in white light-emitting elements with specific dopant concentrations and charge balance in light-emitting layers.
Innovation Solution
The organic light-emitting element is configured with two light-emitting layers, where the first light-emitting layer has a lower content of a red light-emitting material and a shallower HOMO level than the second light-emitting layer, and an electron-blocking layer and hole-blocking layer are used to confine holes and electrons, respectively, while maintaining a delocalized recombination region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the concentration of light-emitting dopants is increased to improve light emission intensity, then the light emission characteristic improves, but the charge balance in the light-emitting layers deteriorates
Solution Approach 1:
The patent applies local quality by creating two distinct light-emitting layers with different dopant concentrations and compositions. The first light-emitting layer contains a first light-emitting dopant at a specific concentration, while the second light-emitting layer contains a second light-emitting dopant at a different concentration. This allows each layer to be optimized locally for both light emission intensity and charge balance, rather than using a uniform composition throughout.
Solution Approach 2:
The patent segments the single light-emitting layer into two separate light-emitting layers. This segmentation allows independent optimization of dopant concentrations and types in each layer, enabling the first layer to emit one color with appropriate charge balance while the second layer emits another color with its own charge balance characteristics, thereby resolving the contradiction between intensity and charge balance.
2Power
If the HOMO level of the first organic compound is made shallower to improve hole injection, then the light emission efficiency improves, but the excitation loss increases
Solution Approach 1:
The patent applies parameter changes by carefully controlling the HOMO level of the first organic compound to be shallower than that of the second organic compound, while simultaneously controlling the LUMO levels to satisfy specific energy level relationships. This precise parameter optimization enables improved hole injection and light emission efficiency while minimizing excitation loss through proper energy level alignment between the organic compounds and light-emitting dopants.
3Reliability
If the content of the first light-emitting material is reduced to improve charge balance, then the charge balance improves, but the light emission intensity from the first layer decreases
Solution Approach 1:
The patent merges the light emission functions of two separate light-emitting layers to achieve overall high light emission intensity while maintaining good charge balance. By combining the emission from the first light-emitting layer (with optimized charge balance) and the second light-emitting layer (with appropriate dopant concentration), the system achieves both improved charge balance and sufficient total light emission intensity that would be difficult to achieve with a single layer.
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 enhances light emission efficiency and durability by reducing excitation loss and suppressing deterioration, thereby improving the overall performance of the organic light-emitting element.
Implementation Method 1
An organic light-emitting element (also referred to as 'organic electroluminescence element' or 'organic EL element' in some cases) is an element that includes a positive electrode, a negative electrode, and an organic compound layer disposed between these electrodes and including a light-emitting layer, and emits light by energizing the organic compound layer
Data Source
AI summary
An organic light-emitting element including a first light-emitting layer that includes a first organic compound, a first light-emitting material, and a second light-emitting material and including a second light-emitting layer that includes a second organic compound and a third light-emitting material, wherein the hole-trapping ability of the first light-emitting layer is mitigated and the recombination region of holes and electrons is kept away from the electrode side of the first light-emitting layer and is also localized in the light-emitting layer by controlling the difference between the HOMO levels of the first light-emitting material and first organic compound in the first light-emitting layer to be smaller than the difference between the LUMO levels of the second organic compound and third light-emitting material in the second light-emitting layer, and reducing the content of the light-emitting material in the first light-emitting layer.