Exciplex OLED Emission Layer With HOMO-Matched Host Compounds
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current light-emitting elements face challenges in achieving high reliability and current efficiency, particularly in controlling carrier balance and recombination probability in the EL layer, which affects their performance and longevity.
Innovation Solution
A light-emitting element structure is developed with an EL layer containing a combination of organic compounds that form an exciplex, where the first organic compound has an electron-transport and hole-transport property, and the second organic compound has a hole-transport property, with a specific HOMO level difference to enhance carrier balance and recombination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional EL layer structure is used, then the device can operate, but carrier balance and recombination probability are insufficient, leading to low reliability and current efficiency
Solution Approach 1:
The EL layer is segmented into multiple functional sub-layers: a first light-emitting sub-layer containing an exciplex-forming combination of host compounds, and a second light-emitting sub-layer containing a different host compound and luminescent dopant. This segmentation allows each sub-layer to be optimized for specific carrier balance and recombination characteristics, improving overall reliability without excessive complexity.
Solution Approach 2:
Different regions of the EL layer are assigned different material compositions and properties. The first light-emitting sub-layer uses compounds with specific HOMO level differences (≤0.4 eV) to optimize electron-hole recombination, while the second sub-layer uses different materials to balance carrier injection. This local optimization of material properties enhances reliability at each stage of the emission process.
2Productivity
If the HOMO level difference between host compounds is large, then carrier injection may be easier, but recombination efficiency and light emission are reduced
Solution Approach 1:
The HOMO level difference between the first and second host compounds is precisely controlled to be 0.4 eV or less. This parameter optimization ensures that carriers can be efficiently injected and transported while maintaining high recombination efficiency in the exciplex region, achieving both low drive voltage and high light emission efficiency.
Solution Approach 2:
The patent employs composite material systems where the first host compound (electron-transporting) and second host compound (hole-transporting) are combined in specific ratios within the light-emitting sub-layers. This composite approach creates an exciplex that facilitates efficient energy transfer and light emission while maintaining optimal carrier balance and low operating voltage.
3Reliability
If a single host compound is used in the EL layer, then the structure is simple, but carrier balance and recombination probability are insufficient
Solution Approach 1:
The EL layer is divided into multiple light-emitting sub-layers, each containing specific combinations of host compounds and luminescent dopants. This segmentation enables independent optimization of carrier balance and recombination efficiency in each sub-layer, achieving high current efficiency while managing the complexity through structured organization.
Solution Approach 2:
The host compounds are selected to perform multiple functions: the first host compound provides electron transport and forms exciplex, while the second host compound provides hole transport and also participates in exciplex formation. This multi-functionality reduces the need for additional specialized materials, improving current efficiency without proportionally increasing 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
This configuration improves the reliability and current efficiency of the light-emitting element by maintaining carrier balance and reducing drive voltage, leading to higher emission efficiency and extended lifespan.
Implementation Method 1
the combination of the first organic compound and the second organic compound forms an exciplex
Implementation Method 2
efficient energy transfer and maintaining recombination efficiency
Implementation Method 3
electrons injected from a cathode and holes injected from an anode recombine in the light emission center of the EL layer to form molecular excitons, and energy is released and light is emitted when the molecular excitons return to the ground state
Data Source
AI summary
To provide a light-emitting element with an improved reliability, a light-emitting element with a high current efficiency (or a high quantum efficiency), and a novel dibenzo[f,h]quinoxaline derivative that is favorably used in a light-emitting element which is one embodiment of the present invention. A light-emitting element includes an EL layer between an anode and a cathode. The EL layer includes a light-emitting layer; the light-emitting layer contains a first organic compound having an electron-transport property and a hole-transport property, a second organic compound having a hole-transport property, and a light-emitting substance; the combination of the first organic compound and the second organic compound forms an exciplex; the HOMO level of the first organic compound is lower than the HOMO level of the second organic compound; and a difference between the HOMO level of the first organic compound and the HOMO level of the second organic compound is less than or equal to 0.4 eV.