Dual Emitting Layer Organic EL Device with Triplet Energy Gradient
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescence devices face limitations in performance, particularly in luminous efficiency and drive voltage, due to inefficiencies in exciton recombination and light extraction, with conventional devices having a theoretical internal quantum efficiency of 25% and high drive voltages.
Innovation Solution
The use of a dual emitting layer structure with host materials in organic electroluminescence devices, where the triplet energy of the first host material is greater than that of the second host material, and the emitting layers are thin enough to satisfy specific thickness ratios, enhancing the Triplet-Triplet Annihilation mechanism and improving light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single emitting layer structure is used, then the device structure is simple, but the internal quantum efficiency is limited to 25% due to singlet-triplet exciton ratio
Solution Approach 1:
The emitting layer is divided into multiple distinct emitting layers (first emitting layer, second emitting layer, and optionally third emitting layer), each with different host materials and triplet energy levels. This segmentation allows different layers to handle different types of excitons efficiently, with lower triplet energy layers converting triplet excitons to singlet excitons through TTF, thereby breaking the 25% efficiency limit of conventional single-layer structures.
Solution Approach 2:
Each emitting layer is assigned specific local properties: the first emitting layer uses a host material with lower triplet energy to facilitate TTF of triplet excitons, while the second emitting layer uses a host material with higher triplet energy to emit light efficiently. This local differentiation of material properties optimizes the overall device performance by matching each layer's function to its specific characteristics.
2Use of energy by moving object
If the emitting layers are made thin to improve light extraction, then light extraction efficiency improves, but the recombination volume decreases
Solution Approach 1:
Instead of using a single thick emitting layer, the structure divides the recombination volume across multiple thin emitting layers. Each layer is thin enough to allow efficient light extraction, but the cumulative recombination volume across all layers is sufficient to maintain high efficiency. The multiple layers work together to balance light extraction and recombination volume.
Solution Approach 2:
The device uses composite material structures with different host materials (first host material with lower triplet energy, second host material with higher triplet energy) in different layers. This composite approach allows each layer to be optimized for its specific function while working together to achieve both thin-film light extraction efficiency and sufficient total recombination volume.
3Use of energy by moving object
If host materials with different triplet energies are used in multiple emitting layers, then Triplet-Triplet Fusion efficiency improves, but the material selection and device fabrication become more complex
Solution Approach 1:
The patent establishes clear local quality criteria for material selection: the first host material must have lower triplet energy than the second host material. This systematic differentiation provides clear fabrication guidelines while enabling efficient TTF. The specific triplet energy relationships create a predictable framework for material selection and device fabrication.
4Use of energy by moving object
If the total film thickness of emitting layers is reduced to 20 nm or less, then light extraction efficiency improves, but the manufacturing precision requirements increase
Solution Approach 1:
The total emitting layer thickness of 20 nm or less is divided across multiple layers (first emitting layer, second emitting layer, and optionally third emitting layer). This segmentation distributes the manufacturing precision requirements across several layers rather than requiring one extremely thin layer, making the fabrication process more manageable while maintaining the thin-film advantage for light extraction.
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 improves luminous efficiency beyond conventional limits, potentially reaching 62.5% internal quantum efficiency and reduces drive voltage by optimizing the separation and interaction of singlet and triplet excitons, while also allowing for closer layer thickness to enhance light extraction.
Implementation Method 1
in order to enhance the performance of the organic EL device, Patent Literature 5 describes a phenomenon in which a singlet exciton is generated by collision and fusion of two triplet excitons (hereinafter, occasionally referred to as a Triplet-Triplet Fusion (TTF) phenomenon)
Implementation Method 2
An organic electroluminescence device (hereinafter, occasionally referred to as 'organic EL device') has found its application in a full-color display for mobile phones, televisions, and the like. When voltage is applied to an organic EL device, holes are injected from an anode and electrons are injected from a cathode into an emitting layer. The injected holes and electrons are recombined in the emitting layer to form excitons.
Data Source
AI summary
An organic EL device includes a first emitting layer and a second emitting layer, in which the first emitting layer contains a first host material, the second emitting layer contains a second host material, the first emitting layer at least contains a first emitting compound that emits light having a maximum peak wavelength of 500 nm or less, the second emitting layer at least contains a second emitting compound that emits light having a maximum peak wavelength of 500 nm or less, a total of a film thickness of the first emitting layer and a film thickness of the second emitting layer is 20 nm or less, and a triplet energy of the first host material T1(H1) and a triplet energy of the second host material T1(H2) satisfy a relationship of (Numerical Formula 1): T1(H1) greater than T1(H2).