OLED Host Material Narrowing Recombination Region
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Solution Overview
Problem
Traditional organic electroluminescence devices with phosphorescent dyes face challenges due to the longer lifetime and greater transfer distance of triplet state excitons, leading to energy loss and complex device structures, which are exacerbated by the need for barrier layers to confine excitons and prevent dopant quenching.
Innovation Solution
Employing a thermally activated delayed fluorescence material with a small energy gap between triplet and singlet state energy levels as the phosphorescence host, reducing the concentration of triplet state excitons and eliminating the need for barrier layers by converting triplet to singlet state energy, thereby narrowing the recombination region and simplifying the device structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent dyes are employed in the luminescent layer, then triplet state exciton energy can be utilized, but the longer lifetime and greater transfer distance of triplet state excitons cause energy loss and require complex barrier layer structures
Solution Approach 1:
The patent changes the energy level parameters of the host material by selecting materials with triplet state energy levels (ET) higher than the phosphorescent dye and singlet state energy levels (ES) appropriately matched. This parameter optimization allows triplet excitons to be confined and converted efficiently without requiring additional barrier layers, thus resolving the contradiction between energy utilization and device complexity
Solution Approach 2:
The patent converts the previously harmful long-lived triplet state excitons that would escape and cause energy loss into a beneficial mechanism by using the host material's triplet state to confine and subsequently convert these excitons into singlet state excitons through energy transfer, which then emit light. This transforms the harmful exciton migration into a useful light emission mechanism
2Loss of energy
If barrier layers are added to confine triplet state excitons and prevent N dopant quenching, then exciton energy loss is reduced, but the device structure becomes more complex
Solution Approach 1:
The host material in the luminescent layer performs multiple functions simultaneously: it confines triplet state excitons through its higher triplet energy level, provides a pathway for triplet-to-singlet conversion, and prevents N dopant quenching through appropriate energy level matching. This self-service capability eliminates the need for separate barrier layers, reducing device complexity while maintaining energy efficiency
Solution Approach 2:
The host material is designed to fulfill multiple roles: exciton confinement, energy transfer medium, and protective barrier against dopant quenching. By making the host material multi-functional, the patent eliminates the need for additional specialized barrier layers, thus reducing device complexity while preventing energy loss
3Loss of energy
If the energy gap between triplet and singlet state energy levels is reduced, then triplet to singlet state conversion is facilitated, but the recombination region becomes narrower requiring precise material selection
Solution Approach 1:
The patent optimizes the energy level parameters by selecting host materials with specific triplet state energy levels (ET) and singlet state energy levels (ES) where ET is higher than the phosphorescent dye and ES is appropriately matched for efficient energy transfer. This parameter optimization facilitates triplet-to-singlet conversion while maintaining a manageable recombination region, balancing conversion efficiency with manufacturing feasibility
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 approach reduces the probability of excitons entering the transport layer, prevents dopant diffusion, and lowers the driving voltage, resulting in improved efficiency and simplified device fabrication.
Implementation Method 1
employs a thermally activated delayed fluorescence material, whose difference between the triplet state energy level and the singlet state energy level (ΔEST) is relatively small, wherein the ΔEST≤2.1 eV
Implementation Method 2
the dye comprises at least one phosphorescent dye... the phosphorescence system can additionally utilize the triplet state exciton energy
Implementation Method 3
Organic electroluminescence devices have drawn the broad attention of people due to the advantages such as thin bodies, large planar sizes, complete fixation and good flexibility
Data Source
AI summary
The present invention discloses an organic electroluminescence device, comprising a luminescent layer, wherein, a host material of the luminescent layer comprises a thermally activated delayed fluorescence material, the host material is doped by a dye, and the dye comprises at least one phosphorescent dye. The present invention employs a thermally activated delayed fluorescence material, whose difference between the triplet state energy level and the singlet state energy level (ΔEST) is relatively small. The present invention employs the material as the phosphorescence host, so part of the triplet state exciton level transfers to the singlet state excitons, and the amount of the overall triplet state excitons is smaller. Therefore, the concentration of the triplet state excitons decreases, and the recombination region becomes narrower, which effectively reduces the probability of excitons entering the charge transport layer, and at the same time the narrowing of the recombination region effective prevents the diffusion of N-type dopants into the exciton recombination region. Additionally, by employing the host material, the device corresponds to a low working voltage.