White Organic EL Device Using Delayed Fluorescent Green Layer
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Solution Overview
Problem
Existing white organic electroluminescent (EL) devices with laminated green, red, and blue sub-emission layers for white light emission face challenges in reducing driving voltage while maintaining high internal quantum efficiency, as phosphorescent materials require higher energy for light emission, increasing voltage and fluorescent materials have lower efficiency.
Innovation Solution
Incorporating a green sub-emission layer with delayed fluorescent material adjacent to the hole transport layer and a red sub-emission layer with phosphorescent light emitting material, where the highest occupied molecular orbital (HOMO) of the delayed fluorescent material is deeper than the hole transport layer and shallower than the phosphorescent material, allowing for efficient light emission with reduced energy barriers and lower driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphorescent light emitting material is used in the red sub-emission layer, then light emission efficiency is improved, but driving voltage increases due to higher energy requirements
Solution Approach 1:
The emission layer is divided into three separate sub-emission layers (green, red, blue) with different light emitting materials. The red sub-emission layer uses phosphorescent material for high efficiency, while the green sub-emission layer uses delayed fluorescent material with lower HOMO level to reduce overall driving voltage. This segmentation allows each layer to be optimized independently for its specific function.
Solution Approach 2:
Different materials with specific local properties are assigned to different sub-emission layers. The delayed fluorescent material in the green layer has a lower HOMO level than the phosphorescent material in the red layer, creating a local energy gradient that facilitates charge transport while maintaining high efficiency in both layers.
2Productivity
If delayed fluorescent material is used in the green sub-emission layer, then internal quantum efficiency is improved, but HOMO level alignment with hole transport layer becomes more challenging
Solution Approach 1:
The HOMO levels of the light emitting materials are carefully selected and adjusted to create a specific energy gradient. The delayed fluorescent material in the green layer has a lower HOMO level than the phosphorescent material in the red layer, which changes the energy landscape to facilitate hole injection and transport while maintaining high internal quantum efficiency.
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 achieves a white organic EL device with low driving voltage and high power efficiency by utilizing the high internal quantum efficiency of delayed fluorescent materials and efficient light emission from phosphorescent materials, improving power efficiency and reducing the need for wide HOMO barriers.
Implementation Method 1
the green sub-emission layer has a delayed fluorescent material
Implementation Method 2
the red sub-emission layer has a phosphorescent light emitting material
Implementation Method 3
white organic electroluminescent (EL) device
Data Source
AI summary
A high-efficiency, white organic electroluminescent device has such a structure that its emission layer is obtained by laminating sub-emission layers of red, green, and blue, respectively. The green sub-emission layer contacting a hole transport layer has a delayed fluorescent material, and the red sub-emission layer has a phosphorescent light emitting material.