Discotic Liquid-Crystalline Host for Phosphorescent OLEDs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional organic electroluminescence elements suffer from low light extraction efficiency due to total reflection at the interface between electrode layers and organic layers, leading to decreased luminous efficiency, polarized emission ratio, and external quantum efficiency.
Innovation Solution
A material comprising a phosphorescent compound with a specific aspect ratio and a discotic liquid-crystalline host compound, where the phosphorescent compound is oriented horizontally with respect to the anode, and a fluorine atom-containing compound is used to enhance light emission efficiency and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a rod-like fluorescent material is used to increase polarized emission ratio, then polarized emission ratio is improved, but light emission efficiency decreases due to Forster energy transfer and reabsorption
Solution Approach 1:
The patent changes the molecular shape parameter from rod-like to disc-like structure, and changes the emission mechanism parameter from fluorescent to phosphorescent. This allows achieving high polarized emission ratio without the energy loss from Forster transfer, as phosphorescent materials have different energy transfer characteristics
Solution Approach 2:
The patent creates a composite light-emitting layer combining disc-like phosphorescent material with liquid crystal host material. This composite structure enables both high polarized emission ratio through liquid crystal orientation and high light emission efficiency through phosphorescent mechanism without Forster transfer losses
2Loss of energy
If a phosphorescent material is oriented with liquid-crystalline host material to avoid Forster energy transfer, then light emission efficiency is improved, but polarized emission ratio and luminescent quantum yield decrease
Solution Approach 1:
The patent changes the molecular shape parameter from rod-like to disc-like structure with specific aspect ratio (2.5-5.0), which enables effective orientation in liquid crystal host material. This specific geometric parameter allows achieving both high polarized emission ratio and high luminescent quantum yield simultaneously
Solution Approach 2:
The patent optimizes the local molecular arrangement by controlling the aspect ratio and orientation of disc-like molecules within the liquid crystal host. This creates a locally optimized structure where molecules are oriented to maximize both light extraction and emission efficiency
3Illumination intensity
If organic layers with high refractive index are used, then display performance is improved, but light extraction efficiency decreases due to total reflection at interfaces
Solution Approach 1:
The patent converts the harmful total reflection effect into a beneficial orientation effect. By using disc-like liquid crystalline materials, the molecular orientation at the interface creates anisotropic optical properties that enable light extraction while maintaining high refractive index benefits for display performance
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 achieves high luminous efficiency, polarized emission ratio, and external quantum efficiency by optimizing the orientation and composition of the phosphorescent and discotic liquid-crystalline host compounds within the organic electroluminescence element.
Implementation Method 1
a phosphorescent compound; and a discotic liquid-crystalline host compound
Implementation Method 2
employing a liquid-crystalline host material to control the shape of a light-emitting compound itself and orientation of the light-emitting compound
Implementation Method 3
layers constituting an organic electroluminescence element have a refractive index higher than air... light emitted tends to be reflected totally at an interface
Data Source
Figure 1
AI summary
A material for organic electroluminescence element, including: a phosphorescent compound; and a discotic liquid-crystalline host compound, wherein the phosphorescent compound has an aspect ratio of molecule core diameter to molecule core thickness (molecule core diameter / molecule core thickness) of at least 3, and wherein a size ratio of the molecular radius of the phosphorescent compound to the molecular radius of the discotic liquid-crystalline host compound (molecular radius of the phosphorescent compound / molecular radius of the discotic liquid-crystalline host compound) is 0.8 to 1.2.