Organic EL Light Emitting Layer Host Assist Dopant Carrier Balance
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Solution Overview
Problem
Existing organic electroluminescence elements suffer from local deterioration and reduced brightness due to concentrated carrier recombination near the interface, which is not adequately controlled by simply adjusting the relationship between the host and assist dopant materials' HOMO and LUMO levels.
Innovation Solution
Incorporating a light emitting layer with a host material and an assist dopant material, where one has high electron mobility and the other high hole mobility, with a mobility ratio of 0.01≦μe/μh≦100, and adjusting the content of the assist dopant material to 20 wt % or more to 70 wt % or less, to balance carrier transportation and recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a light emitting layer includes only host material and light emitting material, then the structure is simple, but carrier recombination concentrates near the interface causing local deterioration
Solution Approach 1:
The patent applies local quality by introducing an assist dopant material with different electron and hole transportation properties at specific locations within the light emitting layer. This creates localized regions with optimized carrier transportation characteristics, allowing balanced carrier recombination throughout the layer rather than concentration at the interface, thereby improving light emitting material durability while maintaining overall structural simplicity.
2Speed
If host material with high electron transportation property is used, then electron mobility is improved, but hole recombination becomes unbalanced causing interface concentration
Solution Approach 1:
The patent applies asymmetry by selecting an assist dopant material with asymmetric transportation properties where electron mobility (μe) is significantly higher than hole mobility (μh), creating a mobility ratio μe/μh of 0.01 to 100. This asymmetric characteristic compensates for the host material's high electron transportation property, balancing the overall carrier recombination distribution throughout the light emitting layer and preventing interface concentration.
3Reliability
If assist dopant material is added to control carrier transportation, then recombination distribution improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by establishing a specific mobility ratio range (μe/μh = 0.01 to 100) as the key controlling parameter rather than precisely controlling individual dopant concentrations. This approach transforms the manufacturing control requirement from multiple concentration parameters to a single ratio parameter, making it easier to achieve balanced carrier recombination distribution while maintaining 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 configuration enhances light emitting characteristics and extends the life span of the organic electroluminescence element by effectively separating the recombination site from the interface, reducing local deterioration and maintaining brightness over time.
Implementation Method 1
one of the host material and the assist dopant material is a material with a high electron transportation property, the other is a material with a high hole transportation property, and when a mobility of holes is μh and a motility of electrons is μe in the light emitting layer
Implementation Method 2
the host material has a role of moving excitation energy, which is generated by the recombination of carriers in molecules of the host material when a voltage is applied between electrodes, to a light emitting material and causing the light emitting material to emit light
Data Source
AI summary
A light emitting element has a cathode, an anode, and a light emitting layer (light emitting section) which is provided between the cathode and the anode and emits light by a driving voltage being applied thereto, in which the light emitting section is configured to include a light emitting material, a host material which holds the light emitting material, and an assist dopant material, one of the host material and the assist dopant material is a material with a high electron transportation property, the other is a material with a high hole transportation property, and when a mobility of holes is μh and a motility of electrons is μe in the light emitting layer, a mobility ratio which is represented by μe/μh satisfies a relationship of formula (I) below.0.01≦μe/μh≦100 (I)