OLED EL Layer Host-Guest Composition for Low-Voltage Emission
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Solution Overview
Problem
Existing light-emitting elements using phosphorescent compounds face limitations in emission efficiency, reliability, emission characteristics, synthesis efficiency, and cost, particularly when using phosphorescent iridium metal complexes as guest materials.
Innovation Solution
Incorporating a phosphorescent iridium metal complex with a diazine skeleton as the first compound and an organic compound with a pyrimidine skeleton as the second compound in the electroluminescent layer, where the second compound serves as a host material, facilitating favorable carrier transfer and low current density, thereby enhancing emission efficiency and lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent iridium metal complexes are used as light-emitting substances, then emission efficiency can be improved, but synthesis cost and complexity increase
Solution Approach 1:
The patent optimizes the LUMO energy level parameter of the phosphorescent iridium complex to fall within -3.0 eV to -2.0 eV, and adjusts the host material's triplet energy level to be higher than the guest material's triplet energy level. These parameter optimizations enable efficient energy transfer while using commercially available iridium complexes with simplified synthesis routes, resolving the contradiction between emission efficiency and synthesis cost.
2Use of energy by moving object
If phosphorescent compounds are used to achieve high internal quantum efficiency, then emission efficiency improves, but device complexity and material selection constraints increase
Solution Approach 1:
The patent establishes specific energy level parameters: the phosphorescent iridium complex has LUMO between -3.0 eV to -2.0 eV, and the host material has triplet energy level higher than the guest's triplet energy level. These quantified parameters provide clear material selection criteria that simplify device design while ensuring high internal quantum efficiency through efficient energy transfer and suppressed concentration quenching.
3Use of energy by moving object
If the LUMO level of the iridium complex is optimized for carrier injection, then emission efficiency improves, but the range of suitable host materials decreases
Solution Approach 1:
The patent specifies the LUMO level of the phosphorescent iridium complex within -3.0 eV to -2.0 eV, which optimizes electron injection efficiency. Simultaneously, it requires the host material's triplet energy level to be higher than the guest's triplet energy level, a condition satisfied by multiple common host materials such as Alq3, BCP, and TPBi. This dual parameter specification maintains host material versatility while achieving high emission efficiency.
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 proposed structure achieves a light-emitting element with low driving voltage, high current efficiency, and reduced power consumption, along with improved evaporation efficiency and stability.
Implementation Method 1
an observation on a compound that can convert energy of a triplet excited state into light emission (hereinafter, called a phosphorescent compound) shows light emission from the triplet excited state (phosphorescence)
Implementation Method 2
research and development have been extensively conducted on light-emitting elements using electroluminescence (EL). In a basic structure of such a light-emitting element, a layer containing a light-emitting material is interposed between a pair of electrodes. By voltage application to this element, light emission can be obtained from the light-emitting substance.
Data Source
AI summary
A light-emitting element includes an EL layer between a pair of electrodes. The EL layer contains a first compound and a second compound. The first compound is a phosphorescent iridium metal complex having a LUMO level of greater than or equal to −3.5 eV and less than or equal to −2.5 eV, and the second compound is an organic compound having a pyrimidine skeleton. The light-emitting element includes an EL layer between a pair of electrodes. The EL layer contains a first compound and a second compound. The first compound is a phosphorescent iridium metal complex having a diazine skeleton, and the second compound is an organic compound having a pyrimidine skeleton.