Light-Emitting Device With Overlapping Fluorescent And Phosphorescent Layers
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Solution Overview
Problem
Current organic electroluminescent devices have limited emission efficiency due to the restrictive triplet energy transfer processes, which restrict the utilization of triplet excited states for light emission.
Innovation Solution
A light-emitting element structure is developed with overlapping first and second light-emitting layers, where the first layer contains a fluorescent material with a higher triplet excited state level than the host material, allowing for both singlet and triplet energy transfer processes to enhance emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional single light-emitting layer structure is used, then device structure is simple, but emission efficiency is limited due to restrictive triplet energy transfer processes
Solution Approach 1:
The light-emitting device is divided into multiple light-emitting layers (first light-emitting layer with fluorescent material, second light-emitting layer with phosphorescent material) instead of using a single light-emitting layer. This segmentation allows different layers to utilize different emission mechanisms (singlet and triplet excited states), thereby improving overall emission efficiency while maintaining manageable device complexity
Solution Approach 2:
The patent transitions from a single-layer structure to a multi-layer vertical structure, adding the dimension of layer stacking. The first and second light-emitting layers are arranged in different spatial positions between the electrodes, with overlapping regions that enable both singlet and triplet energy transfer processes to occur simultaneously in different dimensional zones
2Loss of energy
If overlapping first and second light-emitting layers are used, then both singlet and triplet energy transfer processes are utilized to enhance emission efficiency, but device structure becomes more complex
Solution Approach 1:
The overlapping region of the first and second light-emitting layers serves multiple functions simultaneously: it enables singlet energy transfer from the fluorescent material in the first layer, allows triplet energy transfer to the phosphorescent material in the second layer, and provides spatial overlap for both processes. This multi-functionality improves emission efficiency without proportionally increasing device complexity
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 higher emission efficiency by utilizing both singlet and triplet excited states, exceeding the conventional exciton generation probability and providing a light-emitting element with improved performance.
Implementation Method 1
A fluorescent material refers to a material that emits light in the visible light region when the level of the lowest singlet excited state (S1 level) relaxes to the ground state.
Implementation Method 2
A phosphorescent material refers to a material that emits light in the visible light region at room temperature when the T1 level relaxes to the ground state.
Implementation Method 3
allowing for both singlet and triplet energy transfer processes to enhance emission efficiency
Data Source
AI summary
Provided is a light-emitting element which includes a first electrode, a second electrode over the first electrode, and first and second light-emitting layers therebetween. The first light-emitting layer contains a first host material and a first light-emitting material, and the second light-emitting layer contains a second host material and a second light-emitting material. The first light-emitting material is a fluorescent material, and the second light-emitting material is a phosphorescent material. The level of the lowest triplet excited state (T1 level) of the first light-emitting material is higher than the T1 level of the first host material. A light-emitting device, an electronic device, and a lighting device including the light-emitting element are further provided.