Organic Electroluminescent Element Density Optimization
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Solution Overview
Problem
Conventional organic electroluminescent elements face issues with voltage rise during constant electric current driving, occurrence of dark spots, and reduced stability under high temperature and high humidity conditions, particularly in achieving high luminance and efficiency across various color light emissions.
Innovation Solution
An organic electroluminescent element with specific organic layers having a density of 1.10 to 1.25 g/cm3, incorporating a phosphorescent dopant and host compound with a band gap of 2.5 to 3.8 eV, and controlled organic solvent content, optimized for reduced voltage rise and enhanced stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional organic EL elements are used, then light emission is achieved, but voltage rises during constant electric current driving and dark spots occur
Solution Approach 1:
The patent changes the molecular weight parameter of the host compound to 400-2000, which optimizes the electrical and physical properties of the organic layer. This parameter adjustment reduces voltage rise during constant current driving while maintaining light emission stability, directly resolving the contradiction between reliability and voltage stress.
Solution Approach 2:
The patent uses composite material systems combining specific host compounds (molecular weight 400-2000) with phosphorescent dopants and charge transport layers. This composite approach creates synergistic effects that improve overall element stability and reduce voltage rise, addressing the reliability-voltage contradiction.
2Reliability
If conventional organic EL elements are used, then light emission is achieved, but dark spots occur and durability under high temperature and humidity deteriorates
Solution Approach 1:
The patent adjusts the molecular weight parameter of the host compound to 400-2000, which optimizes moisture and heat resistance properties. This parameter change enhances durability under high temperature and humidity conditions while preventing dark spot formation, directly resolving the contradiction between reliability and environmental resistance.
Solution Approach 2:
The patent employs organic compounds with molecular weights in the 400-2000 range that provide sufficient stability for practical applications without requiring extremely complex or expensive molecular structures. This approach achieves adequate durability under harsh conditions while maintaining practical manufacturability.
3Use of energy by moving object
If phosphorescent light emission is utilized, then internal quantum efficiency reaches 100%, but sufficient taking out efficiency cannot be obtained for certain color lights
Solution Approach 1:
The patent selects host compounds with molecular weights of 400-2000 and appropriate band gaps that optimize both internal quantum efficiency and light extraction efficiency. This parameter optimization ensures that phosphorescent emission is efficiently generated and extracted, resolving the contradiction between internal efficiency and external light output.
Solution Approach 2:
The patent optimizes the local properties of the light emission layer by selecting host compounds with specific molecular weights and band gaps that are tailored for efficient phosphorescent emission and light extraction. This localized optimization of material properties addresses the efficiency extraction problem for different color lights.
4Illumination intensity
If blue light emission with high efficiency is required, then compounds with larger band gap are demanded, but manufacturing complexity increases
Solution Approach 1:
The patent establishes a specific molecular weight range (400-2000) for host compounds that enables efficient blue light emission without requiring excessively complex molecular structures. This parameter constraint simplifies the search and selection process while maintaining high blue light emission efficiency, resolving the contradiction between performance and manufacturing complexity.
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
The solution effectively reduces voltage rise and dark spots while improving aging stability and luminance, particularly under high temperature and humidity conditions, and enhances light emission efficiency across different colors.
Implementation Method 1
the element emits light by utilizing the light emission (fluorescence or phosphorescence) caused by quenching of exciton generated by recombination of an electron and a positive hole injected from the electrodes to the light emission layer
Implementation Method 2
an organic EL element using phosphorescent light emitted from the triplet excited state
Data Source
AI summary
This invention provides an organic electroluminescent element comprising a substrate and an electrode and one or more organic layers provided on the substrate. The organic electroluminescent element is characterized in that the layer density of at least one of the organic layers is 1.10 to 1.25 g/cm3. The organic electroluminescent element exhibits good luminescence brightness, causes no significant voltage rise and dark spot in the constant-current driving, and has good temporal stability under high temperature and high humidity conditions. There are also provided a display device and a lighting device using the organic EL element.