Blue Phosphorescent OLED Host Material Ionization Potential Configuration
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Solution Overview
Problem
Current blue phosphorescent organic electroluminescent elements face challenges in achieving high luminous efficiency and driving durability due to the difficulty in injecting electric charges with host materials having a triplet energy of 272 kJ/mol or more, which affects the combination of these two performance metrics.
Innovation Solution
The use of a blue phosphorescent luminescent material and a host material with a triplet energy of 272 kJ/mol or more, combined with a specific configuration of luminescent and charge transport layers, where the ionization potentials and electron affinities between layers satisfy predetermined relationships, such as Ip1>Ip2>Ip3 and Ea1<Ea2<Ea3, to enhance charge injection and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a host material with T1 energy of 272 kJ/mol or more is used to achieve high luminous efficiency, then luminous efficiency is improved, but charge injection becomes difficult and driving durability deteriorates
Solution Approach 1:
The device is divided into multiple charge transport layers with different energy level characteristics. The first charge transport layer has higher ionization potential/electron affinity to facilitate charge injection from the electrode, while the second charge transport layer has lower ionization potential/electron affinity to enable efficient charge transport to the luminescent layer, resolving the contradiction between charge injection and charge transport
Solution Approach 2:
Different regions of the charge transport system are assigned different energy level properties. The region adjacent to the electrode (first charge transport layer) has optimized properties for charge injection, while the region adjacent to the luminescent layer (second charge transport layer) has optimized properties for charge transport, allowing each region to perform its specific function optimally
2Reliability
If the ionization potential and electron affinity relationships between layers are optimized to improve charge injection, then driving durability is improved, but device complexity increases
Solution Approach 1:
The invention changes the energy level parameters (ionization potential and electron affinity) of the charge transport layers to satisfy specific relationships: Ip1>Ip2>Ip3 for ionization potentials and Ea1<Ea2<Ea3 for electron affinities. This systematic parameter optimization enables improved charge injection and driving durability while maintaining a relatively simple multi-layer structure
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 a blue phosphorescent organic electroluminescent element with improved luminous efficiency and driving durability, as it promotes efficient electric charge injection and reduces material degradation at interfaces.
Implementation Method 1
An organic electroluminescent element is made of an organic compound layer that includes at least a luminescent layer and a pair of electrodes that sandwich the organic compound layer. When an electric field is applied between both electrodes, electrons are injected from a cathode and holes are injected from an anode. The electrons and holes recombine in a luminescent layer to luminesce.
Implementation Method 2
A blue phosphorescent luminescent material and a host material having a T1 energy of 272 kJ/mol (65 kcal/mol) or more are used in the luminescent layer. The blue phosphorescent luminescent material normally has the lowest excited triplet energy (T1) of 272 kJ/mol (65 kcal/mol) or more.
Data Source
AI summary
The present invention provides an organic electroluminescent element that includes a pair of electrodes and a plurality of organic compound layers being disposed between the pair of electrodes. The organic compound layers include a luminescent layer containing a blue phosphorescent luminescent material and a host material having the lowest excited triplet energy (T1) of 272 kJ/mol (65 kcal/mol) or more, and hole transport layers. One of the hole transport layers is a layer adjacent to the luminescent layer, and when the ionization potentials of the luminescent layer, the hole transport layer adjacent to the luminescent layer, and another of the hole transport layers, respectively, designated to Ip1, Ip2 and Ip3, the relationship Ip1>Ip2>Ip3 is satisfied.