Quinoxaline Derivative Electron-Trapping Layer for OLED Lifetime
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Solution Overview
Problem
Current light-emitting elements with phosphorescent materials have short lifetimes due to the poor durability of hole-blocking layers, leading to inefficient light emission and reduced longevity.
Innovation Solution
Incorporating a substance with electron-trapping properties in the electron-transporting layer, specifically using a quinoxaline derivative with an energy gap higher than the light-emitting substance, to control electron transfer and maintain carrier balance, thereby enhancing the lifetime and color purity of the light-emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a hole-blocking layer is formed to improve light emission efficiency, then light emission efficiency is improved, but durability deteriorates and lifetime is shortened
Solution Approach 1:
The invention extracts the hole-blocking function from a separate layer structure and integrates it into the electron-transporting layer through material selection. By choosing a material with appropriate LUMO level (lower than the light-emitting substance by 0.3 eV or more), the layer simultaneously transports electrons and blocks holes, eliminating the need for a separate hole-blocking layer that would compromise durability.
Solution Approach 2:
The electron-transporting layer is designed to perform multiple functions: electron transport and hole blocking. This multi-functional design eliminates the need for additional specialized layers, reducing structural complexity and potential failure points while maintaining efficient light emission.
2Speed
If the LUMO level of the electron-transporting material is lowered to improve electron transport, then electron transport is improved, but electron leakage increases and carrier balance is disrupted
Solution Approach 1:
The invention optimizes the LUMO level parameter of the electron-transporting material to a specific range: lower than the light-emitting substance by 0.3 eV or more but not excessively low. This parameter optimization enables efficient electron transport while preventing electron leakage to the hole-transporting layer, thereby maintaining carrier balance.
Solution Approach 2:
The carrier balance is dynamically maintained through the energy level alignment. The LUMO level is positioned to allow electron injection from the electrode and transport through the layer, while the energy gap prevents electrons from reaching the hole-transporting layer, adapting to the operational conditions of the light-emitting element.
3Duration of action of stationary object
If a substance with electron-trapping property is added to control electron transfer, then lifetime is extended, but the substance may emit light and reduce color purity
Solution Approach 1:
The invention applies local quality by selecting an electron-trapping substance with specific properties: high LUMO level (lower than light-emitting substance by 0.3 eV or more) and energy gap larger than the light-emitting substance. This ensures the substance traps electrons to extend lifetime while its energy gap prevents light emission that would compromise color purity.
Solution Approach 2:
The energy gap parameter of the electron-trapping substance is specifically chosen to be larger than that of the light-emitting substance. This parameter change ensures that even if the electron-trapping substance is excited, it cannot emit light in the visible range, thus maintaining color purity while extending device lifetime.
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 results in light-emitting elements with extended lifetimes and improved color purity by controlling electron transfer and preventing unnecessary light emission from the electron-trapping substance, leading to more stable and efficient light emission.
Implementation Method 1
Incorporating a substance with electron-trapping properties in the electron-transporting layer, specifically using a quinoxaline derivative
Implementation Method 2
electrons and holes are injected into a layer including a light-emitting organic compound from a pair of electrodes by voltage application to a light-emitting element, so that current flows therethrough. The electrons and holes (i.e., carriers) are recombined, and thus the light-emitting organic compound is excited. The light-emitting organic compound returns to a ground state from the excited state, thereby emitting light.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The present invention provides light-emitting element having long lifetime, and light-emitting devices and electronic devices having long lifetime. A light-emitting element comprises a first layer and a second layer including a light-emitting substance between a first electrode and a second electrode. The first layer includes a first organic compound and a second organic compound, the first layer is formed between the second layer and the second electrode, the first layer includes the first organic compound more than the second organic compound, the first organic compound is an organic compound having an electron-transporting property, the second organic compound is an organic compound having an electron-trapping property, an energy gap of the second organic compound is larger than that of the light-emitting substance; and a voltage is applied such that a potential of the first electrode is higher than that of the second electrode, so that the light-emitting layer emits light.