Stacked White OLED With Charge-Generating Layers
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Solution Overview
Problem
Conventional white organic light-emitting diodes (WOLEDs) face challenges in achieving high efficiency and color rendering index (CRI) at high brightness, particularly in indoor lighting applications, due to difficulties in balancing exciton formation and optical interference within multiple emissive layers.
Innovation Solution
A stacked OLED structure with vertically stacked red, green, and blue sub-elements separated by transparent charge-generating layers, optimized for charge balance and microcavity effects, achieving balanced white emission and high efficiency through specific layer thickness adjustments and charge balancing mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple emissive layers are stacked to achieve high brightness and color rendering, then the color rendering index and brightness are improved, but the efficiency deteriorates due to unbalanced exciton formation and optical interference
Solution Approach 1:
The device divides the white light emission into three separate emissive sub-elements (red, green, blue) stacked vertically, each responsible for a specific color range. This segmentation allows independent optimization of each sub-element's exciton formation and light extraction, avoiding the efficiency losses associated with unbalanced multi-layer emission in conventional WOLEDs.
Solution Approach 2:
The patent transitions from a planar multi-layer structure to a vertical stacked configuration, utilizing the third dimension (depth) to separate the emissive layers. This vertical arrangement reduces optical interference between layers and enables better control of exciton formation in each sub-element, thereby maintaining high efficiency while achieving superior brightness and color rendering.
2Illumination intensity
If multiple emissive layers are stacked to achieve high brightness and color rendering, then the color rendering index is improved, but the device complexity increases due to multiple charge-generating layers and charge balancing mechanisms
Solution Approach 1:
The charge-generating layers serve multiple functions: they generate charge carriers for adjacent emissive sub-elements, act as charge extraction interfaces, and provide mechanical separation between layers. This multi-functionality reduces the need for additional specialized layers, thereby managing device complexity while achieving high color rendering index through the stacked configuration.
3Use of energy by moving object
If layer thickness is adjusted to optimize charge balance and microcavity effects, then the external quantum efficiency is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent systematically varies the thickness parameters of charge-generating layers and emissive sub-elements to optimize both charge balance and microcavity effects. By carefully controlling these dimensional parameters, the design achieves enhanced external quantum efficiency through constructive optical interference and balanced charge injection, while the specific thickness values provided in the patent serve as manufacturable targets.
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 solution results in a WOLED with a total external quantum efficiency of at least 28% at 1000 cd/m² and a CRI of 75 or higher, suitable for indoor lighting, by optimizing the order and thickness of sub-elements and using charge-generating layers like MoO3 for efficient charge injection and extraction.
Implementation Method 1
transparent charge-generating layers, optimized for charge balance and microcavity effects, achieving balanced white emission
Implementation Method 2
using charge-generating layers like MoO3 for efficient charge injection and extraction
Implementation Method 3
A stacked OLED structure with vertically stacked red, green, and blue sub-elements separated by transparent charge-generating layers
Implementation Method 4
optimized for charge balance and microcavity effects, achieving balanced white emission
Data Source
Figure 1
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Figure 3(A)~3(B)
AI summary
The present invention relates to efficient organic light emitting devices (OLEDs). More specifically, the present invention relates to white-emitting OLEDs, or WOLEDs. The devices of the present invention employ three emissive sub-elements, typically emitting red, green and blue, to sufficiently cover the visible spectrum. The sub-elements are separated by charge generating layers.