Organic Electroluminescence Host Material System for Efficiency and Lifetime
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Solution Overview
Problem
Phosphorescent host materials in organic electroluminescence devices have a large HOMO, making hole injection difficult, leading to short device lifetime and reduced luminous efficiency.
Innovation Solution
A combination of specific first and second host materials in the emitting layer, represented by specific chemical formulas, is used to enhance luminous efficiency and extend device lifetime, with the first host material being a compound with a nitrogen-containing heteroaromatic ring and the second host material having a substituted or unsubstituted fused aromatic cyclic group, optimizing the emission peak wavelength between 490 nm to 700 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a phosphorescent host material with a large HOMO is used, then the device can achieve high luminous efficiency by utilizing singlet and triplet states, but hole injection becomes difficult resulting in short device lifetime
Solution Approach 1:
The patent employs a composite host material system consisting of a phosphorescent host material combined with a specific compound (formula 1) having appropriate HOMO level. This composite approach allows the system to maintain the high luminous efficiency of phosphorescent materials while the second compound provides suitable hole injection characteristics, thereby resolving the contradiction between energy utilization and device stability
Solution Approach 2:
The patent modifies the HOMO level parameter of the host material by introducing a compound with specifically designed molecular structure (formula 1 with nitrogen-containing heteroaromatic rings and fused cyclic structures). This parameter adjustment enables optimal hole injection while preserving the phosphorescent emission characteristics, balancing luminous efficiency and device lifetime
2Productivity
If a phosphorescent host material is used to utilize both singlet and triplet excitons, then luminous efficiency increases three to four times, but emission occurs at the interface of hole transporting layer due to difficult hole injection
Solution Approach 1:
The compound represented by formula (1) acts as an intermediary material between the phosphorescent dopant and the hole transporting layer. It facilitates hole injection into the emitting layer while maintaining the phosphorescent emission properties, preventing emission from occurring at the interface and ensuring stable device operation
Solution Approach 2:
The patent introduces a material with specific local chemical properties (nitrogen-containing heteroaromatic rings with particular HOMO levels) at strategic positions in the emitting layer. This localized quality adjustment enables effective hole injection at specific regions while preserving the overall phosphorescent emission characteristics throughout the layer
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 combination of host materials results in a long-life organic electroluminescence device with high luminous efficiency, improving the device's operational stability and emission characteristics.
Implementation Method 1
A phosphorescent organic EL device using a phosphorescent dopant material as a luminescent material has been known as the organic EL device. The phosphorescent organic EL device can achieve a high luminous efficiency by using a singlet state and a triplet state of excited states of the phosphorescent dopant material.
Implementation Method 2
an organic electroluminescence device that includes an emitting unit (in which an emitting layer is included) between an anode and a cathode and emits light using exciton energy generated by a recombination of holes and electrons that have been injected into the emitting layer
Data Source
AI summary
The organic electroluminescence device includes an anode, a cathode, and at least an emitting layer between the anode and the cathode. The emitting layer includes a first host material, a second host material, and a phosphorescent dopant material. The first host material is a compound represented by a formula (1) below and the second host material is a compound represented by a formula (2) below.