Tandem Organic Light-Emitting Element with TTF Host for Carrier Loss Reduction
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Solution Overview
Problem
White tandem light-emitting elements face issues with high drive voltage, efficiency loss due to carrier loss in intermediate layers, and low productivity, as well as challenges in efficiently generating and emitting red, green, and blue light due to energy transfer limitations between layered light-emitting materials.
Innovation Solution
A light-emitting element with a three-layer structure comprising a first light-emitting layer with a host material and a TTF material, a second light-emitting layer with a thermally activated delayed fluorescent material, and a third light-emitting layer with a fluorescent material, where the excited triplet level of the host material or TTF material in the first layer is lower than the thermally activated delayed fluorescent material in the second layer, allowing for Dexter and Förster energy transfers to achieve efficient three-color light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a white tandem structure with multiple EL elements is used to achieve white light emission, then the light emission capability is improved, but the drive voltage increases and efficiency decreases due to carrier loss in intermediate layers
Solution Approach 1:
The patent combines red, green, and blue light-emitting layers into a single integrated functional layer, eliminating the need for multiple separate EL elements and intermediate layers. This merging approach maintains white light emission capability while removing the source of carrier loss that occurs in tandem structures.
Solution Approach 2:
The patent extracts and eliminates the intermediate layer from the tandem structure, which is the source of carrier loss. By using a single functional layer with directly adjacent R, G, and B light-emitting layers, the problematic intermediate layer is removed entirely while preserving the white light emission function.
2Illumination intensity
If a white tandem structure with multiple EL elements is used to achieve white light emission, then the light emission capability is improved, but the device complexity and manufacturing difficulty increase due to many layers
Solution Approach 1:
The patent merges multiple EL elements into a single integrated structure where red, green, and blue light-emitting layers coexist in one functional layer. This reduces the number of discrete layers and simplifies the overall device architecture while maintaining white light emission capability.
Solution Approach 2:
The patent segments the white light emission function into three distinct light-emitting layers (R, G, B) within a single functional layer, each responsible for emitting a specific color. This segmentation allows for simplified manufacturing compared to assembling multiple complete EL elements, as the layers can be formed in a single fabrication process.
3Device complexity
If red, green, and blue light-emitting layers are simply layered to achieve three-color emission, then the structure is simplified, but it is difficult to generate excitons efficiently over all layers and emit lights of three colors
Solution Approach 1:
The patent applies local quality by assigning specific host materials to specific light-emitting layers based on their energy level requirements. The first light-emitting layer (shortest wavelength) uses a host material with a triplet energy level lower than the TTF material, the second layer (intermediate wavelength) uses a TADF material with intermediate energy levels, and the third layer (longest wavelength) uses a fluorescent material. This localized optimization ensures efficient exciton generation and energy transfer in each region.
Solution Approach 2:
The patent changes the energy level parameters of host materials and light-emitting materials in each layer to enable efficient energy transfer. By carefully selecting materials with appropriate triplet energy levels (T1) and singlet energy levels (S1), the patent ensures that energy can transfer from the first layer to the second layer and from the second layer to the third layer, enabling efficient three-color emission.
4Device complexity
If energy transfer between layered light-emitting materials is used to achieve three-color emission, then the structure is simplified, but the energy transfer occurs only by specific material combinations with overlapping emission and absorption spectra
Solution Approach 1:
The patent systematically adjusts the energy level parameters (triplet energy T1 and singlet energy S1) of host materials and light-emitting materials to enable efficient energy transfer. The first light-emitting layer uses a host material with T1 lower than the TTF material, the second layer uses a TADF material with intermediate energy levels, and the third layer uses a fluorescent material with the lowest energy levels. This parameter optimization enables versatile material selection while ensuring efficient energy transfer.
Solution Approach 2:
The patent introduces a TTF material as an intermediary in the first light-emitting layer that facilitates energy transfer to the TADF material in the second layer. The TTF material acts as a bridge, accepting energy from the host material and transferring it to the TADF material, enabling efficient energy transfer across layers with different energy level requirements.
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 enables efficient light emission of three colors with different peak wavelengths at a lower cost, enhancing the internal quantum efficiency and reducing the complexity of the light-emitting element structure.
Implementation Method 1
The light-emitting element emits light by using release of light during deactivation of excitons that are generated by injecting electrons (e−) and holes (h+) into the light-emitting layer and causing recombination
Implementation Method 2
allowing for Dexter and Förster energy transfers to achieve efficient three-color light emission
Implementation Method 3
allowing for Dexter and Förster energy transfers to achieve efficient three-color light emission
Implementation Method 4
The second light-emitting layer contains at least a thermally activated delayed fluorescent material
Data Source
AI summary
An organic EL element (10) includes a first light-emitting layer (33a) having the shortest emission peak wavelength of a light-emitting layer (33) and containing a host material and a TTF material or at least the TTF material, a second light-emitting layer (33b) containing at least a TADF material, a third light-emitting layer (33c) having the longest emission peak wavelength of the light-emitting layer (33) and containing at least fluorescent material. The excited triplet level of the TTF material is lower than the excited triplet level of the TADF material.