OLED Mixed-Layer Architecture for Lifetime and Emission Efficiency
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Solution Overview
Problem
Existing organic electroluminescent devices using delayed fluorescent materials face challenges in achieving both high emission efficiency and long device lifetime, with increased concentration of delayed fluorescent materials in the light-emitting layer leading to reduced luminescent quantum efficiency and high drive voltage.
Innovation Solution
The organic light-emitting device incorporates multiple delayed fluorescent materials with specific energy level requirements, forming a mixed layer adjacent to the light-emitting layer, comprising compounds with varying lowest excited singlet energy levels and controlled content ratios to enhance energy transfer and emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the concentration of delayed fluorescent material in the light-emitting layer is increased to improve device lifetime, then the lifetime is extended, but the luminescent quantum efficiency decreases
Solution Approach 1:
The patent introduces a mixed layer containing multiple delayed fluorescent materials with different energy levels as an intermediary between the light-emitting layer and the charge transport layers. This mixed layer mediates the energy transfer process, allowing triplet excitons to be efficiently converted and transferred without requiring high concentrations of delayed fluorescent material in the light-emitting layer itself, thus resolving the contradiction between lifetime and quantum efficiency
Solution Approach 2:
The patent changes the energy level parameters of the delayed fluorescent materials by selecting compounds with specific HOMO and LUMO levels, as well as different lowest excited singlet energy levels (ES1). By optimizing these parameters in the mixed layer, the system achieves both long lifetime and high quantum efficiency through controlled energy transfer pathways
2Duration of action of stationary object
If the concentration of delayed fluorescent material in the light-emitting layer is increased to improve device lifetime, then the lifetime is extended, but the drive voltage increases
Solution Approach 1:
The mixed layer acts as an intermediary that facilitates efficient charge and energy transfer between the light-emitting layer and the charge transport layers. This intermediary function reduces the need for high delayed fluorescent material concentrations in the light-emitting layer, thereby maintaining lower drive voltage while still achieving extended device lifetime
Solution Approach 2:
The patent uses a composite structure with a mixed layer containing multiple delayed fluorescent materials (e.g., 4CzIPN and 4CzTPN) combined with host materials. This composite approach optimizes both charge transport and energy transfer properties, achieving long lifetime without the penalty of high drive voltage that would result from simply increasing delayed fluorescent material concentration
3Device complexity
If a single delayed fluorescent material is used in the light-emitting layer to simplify device structure, then the device complexity is reduced, but the emission efficiency is limited
Solution Approach 1:
The patent segments the device into distinct functional layers: a light-emitting layer and a separate mixed layer. The mixed layer contains multiple delayed fluorescent materials with different energy levels that work together to enhance emission efficiency through energy transfer, while the light-emitting layer maintains a simpler composition. This segmentation allows complex material combinations to improve efficiency without overly complicating the overall device structure
Solution Approach 2:
The patent adds a new dimensional aspect to the device architecture by introducing a mixed layer with multiple energy levels. This creates an additional energy transfer pathway dimension, where excitons can transfer through multiple materials with different ES1 levels, thereby enhancing emission efficiency without simply increasing the concentration of a single material
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 results in an organic light-emitting device with improved light emission efficiency and extended lifetime, while maintaining a suppressed drive voltage.
Implementation Method 1
A delayed fluorescent material is a compound which, in an excited state, after having undergone reverse intersystem crossing from an excited triplet state to an excited singlet state, emits fluorescence when returning back from the excited singlet state to a ground state
Implementation Method 2
emits fluorescence when returning back from the excited singlet state to a ground state
Implementation Method 3
The inventors have further found that a long lifetime and a high emission efficiency can also be realized by forming a layer containing such multiple delayed fluorescent materials as a layer neighboring to the light-emitting layer
Data Source
AI summary
An organic light-emitting device having an organic mixed layer that contains a first organic compound and a second organic compound and a third organic compound satisfying ES1(A)>ES1(B)>ES1(C). ES1(A), ES1(B) and ES1(C) each represent a lowest excited singlet energy level of the first organic compound, the second organic compound and the third organic compound, respectively. The second organic compound and the third organic compound are delayed fluorescent materials. The invention provides an organic light-emitting device having a long lifetime and a high light emission efficiency.