Organic EL Emitting Layer Structure for Low-Voltage TADF Efficiency
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Solution Overview
Problem
Existing organic electroluminescence devices using a TADF mechanism face limitations in achieving efficient light emission at lower voltages and higher efficiencies.
Innovation Solution
The device incorporates a specific compound arrangement in the emitting layer and adjacent layers, with the emitting layer containing a fluorescent compound and a delayed fluorescent compound, and the adjacent layers containing compounds represented by specific formulas, optimizing the layer structure to enhance hole injectability and exciton generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluorescent organic EL device uses only singlet excitons for light emission, then the device structure is simple, but the internal quantum efficiency is limited to 25%
Solution Approach 1:
The patent changes the energy level parameters of the emitting layer materials, specifically setting the triplet energy level of the host material higher than the singlet energy level of the guest material. This parameter change enables efficient triplet exciton transfer and TADF mechanism, achieving internal quantum efficiency exceeding 25% while maintaining device structure simplicity
Solution Approach 2:
The patent employs composite materials in the emitting layer, combining a host material (e.g., mCP or TCTA) with a guest material (fluorescent or TADF compound). This composite structure enables both simple device fabrication and high internal quantum efficiency by utilizing triplet exciton transfer from host to guest and subsequent TADF or fluorescence emission
2Productivity
If the organic EL device uses triplet excitons in addition to singlet excitons via TADF mechanism, then the internal quantum efficiency is improved, but the operating voltage increases
Solution Approach 1:
The patent optimizes the energy level parameters by setting the LUMO level of the electron transporting layer higher than the triplet energy level of the emitting layer, and the HOMO level of the hole transporting layer lower than the singlet energy level of the emitting layer. These parameter changes enable efficient exciton generation while maintaining low operating voltage
Solution Approach 2:
The patent applies different material properties to different layers: the hole transporting layer uses materials with appropriate HOMO levels for efficient hole injection, the electron transporting layer uses materials with appropriate LUMO levels for efficient electron injection, and the emitting layer uses host-guest combinations with optimized energy levels. This local optimization of material properties achieves both high efficiency and low operating voltage
3Productivity
If the energy difference between singlet and triplet energy levels (ΔST) is reduced for TADF mechanism, then the efficiency of triplet exciton utilization is improved, but the material design complexity increases
Solution Approach 1:
The patent changes the energy level parameters by selecting host materials with high triplet energy levels and guest materials with appropriate singlet energy levels, achieving small ΔST values that enable efficient TADF without complex molecular design
Solution Approach 2:
The patent uses the host material as an intermediary that receives triplet excitons and transfers them to the guest material. This intermediary approach simplifies material design because the host material handles the triplet exciton management, allowing the guest material to focus on light emission properties
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 light emission efficiency and reduces operating voltage by enhancing hole injectability and exciton generation in the emitting layer.
Implementation Method 1
When a voltage is applied to an organic electroluminescence device, holes are injected from an anode and electrons are injected from a cathode into an emitting layer. The injected electrons and holes are recombined in the emitting layer to form excitons.
Implementation Method 2
This TADF mechanism uses such a phenomenon in which inverse intersystem crossing from triplet excitons to singlet excitons thermally occurs when a material having a small energy difference (ΔST) between singlet energy level and triplet energy level is used.
Data Source
AI summary
An organic EL device includes an emitting layer, a first layer adjacent to an anode-side of the emitting layer, and a second layer adjacent to a cathode-side thereof. The emitting layer contains first to third compounds. The first and second layers contain compounds of Formulae (1) and (2), respectively. The first and second compounds exhibits fluorescence and delayed fluorescence, respectively. Singlet energies S1 of the first to third compounds satisfy S1(M3)>S1(M2)>S1(M1). In Formula (1), Ra1-Ra5, Rb1-Rb5 and Rc1-Rc5 are each a substituent, etc. In Formula (2), X1-X3 are each nitrogen atom, etc, Ar1-Ar2 are each a group of Formula (2A) or aryl group, etc, A is a group of Formula (2A) in which HAr is of Formula (2B), a is 1 to 5, L1 is a linking group, etc. In Formula (2B), X11-X18 are each nitrogen atom, etc, and Y1 is oxygen, sulfur or nitrogen atom, etc,