Hybrid OLED Using Fluorescent Blue and Phosphorescent Layers
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Solution Overview
Problem
White OLEDs using only phosphorescent emissive materials have limited operation stability due to the lifetime of the blue phosphorescent component, while those using only fluorescent emissive materials have lower external quantum efficiency.
Innovation Solution
The development of organic light emitting devices that combine fluorescent and phosphorescent emitters, with a specific architecture including a cathode, a fluorescent blue emissive layer, a phosphorescent emissive layer, and an anode, where the combined emission spans the visible spectrum to achieve white emission, and optionally include a spacer layer to enhance efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If only phosphorescent emissive materials are used in white OLEDs, then external quantum efficiency is improved, but operational stability deteriorates due to the limited lifetime of the blue phosphorescent component
Solution Approach 1:
The emissive layer is segmented into multiple distinct layers: a fluorescent blue emissive layer and a phosphorescent emissive layer (containing green and red phosphorescent materials). This segmentation allows each layer to use materials optimized for its specific function, with the fluorescent layer providing long-lived blue emission and the phosphorescent layer providing high-efficiency green and red emission, thereby resolving the contradiction between efficiency and stability.
Solution Approach 2:
Different regions of the emissive structure are assigned different material properties: the blue emissive region uses fluorescent materials with long operational lifetime, while the green and red emissive regions use phosphorescent materials with high external quantum efficiency. This local differentiation of material quality allows each region to contribute its strength, achieving both stability and efficiency in the overall device.
2Reliability
If only fluorescent emissive materials are used in white OLEDs, then operational stability is improved, but external quantum efficiency deteriorates
Solution Approach 1:
The emissive layer is segmented into multiple distinct layers: a fluorescent blue emissive layer and a phosphorescent emissive layer (containing green and red phosphorescent materials). This segmentation allows each layer to use materials optimized for its specific function, with the fluorescent layer providing long-lived blue emission and the phosphorescent layer providing high-efficiency green and red emission, thereby resolving the contradiction between efficiency and stability.
Solution Approach 2:
The emissive region employs a composite structure combining fluorescent and phosphorescent materials in separate layers. The fluorescent blue emitter and phosphorescent green/red emitters work together in a composite emissive system, allowing the device to achieve both the operational stability of fluorescent materials and the high external quantum efficiency of phosphorescent materials.
3Use of energy by moving object
If a combined emissive layer contains both fluorescent and phosphorescent materials, then external quantum efficiency is improved, but device complexity increases
Solution Approach 1:
Rather than mixing fluorescent and phosphorescent materials in a single complex layer, the invention segments them into separate but adjacent emissive layers. This segmentation simplifies the overall structure by giving each layer a single primary function (fluorescent blue emission or phosphorescent green/red emission), making fabrication and material selection more straightforward while still achieving high external quantum efficiency through the combined output of both 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 combination achieves a high external quantum efficiency of at least 4.5% and improved operational stability with a balanced efficiency and lifetime, maintaining high color-stability over a wide range of currents or luminances.
Implementation Method 1
a first emissive layer comprising a fluorescent blue emitting material
Implementation Method 2
a second emissive layer comprising a phosphorescent emitting material
Data Source
AI summary
The present invention provides organic light emitting devices having a combined emission from at least two emissive materials, a fluorescent blue emissive material and a phosphorescent emissive material. The device may further comprise additional fluorescent or phosphorescent emissive materials. In preferred embodiments, the invention provides OLEDs having three different emissive materials—a red emissive material, a green emissive material and a blue emissive material. The invention provides a device architecture which is optimized for efficiency and lifetime by using a combination of fluorescent and phosphorescent emitters. Further, in preferred embodiments the device architecture provides a high color-stability of the light emission over a wide range of currents or luminances.