Organic EL Device Donor-Acceptor Electron Injection Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing organic electroluminescence (EL) devices using a light-transmissive cathode face issues with efficiency and lifespan due to the degradation of electron-injecting layers and increased driving voltage, particularly when using indium-tin-oxide (ITO) as a cathode.
Innovation Solution
The implementation of an organic EL device configuration with a donor-containing layer and an acceptor-containing layer, where the acceptor layer draws electrons from the cathode and transfers them to the donor layer, which then injects them into the emitting layer, using specific compounds resistant to sputtering damage, such as those represented by formulas (I) and (II), to facilitate efficient electron transport and reduce voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light-transmissive cathode (ITO) is used to outcouple light, then light extraction efficiency is improved, but electron-injection properties deteriorate due to large affinity level difference with electron-transporting layer
Solution Approach 1:
An electron-injecting layer is introduced between the light-transmissive cathode (ITO) and the electron-transporting layer. This intermediary layer has affinity levels that bridge the gap between the cathode and the electron-transporting layer, enabling effective electron injection while maintaining light transparency of the cathode.
Solution Approach 2:
The electron-injecting layer is formed as a composite material comprising an organic compound and a metal component (such as alkali metal, alkaline earth metal, or their compounds). This composite structure combines the benefits of organic materials (compatibility with electron-transporting layer) and metal components (low work function for electron injection), resolving the contradiction between light transmittance and electron injection efficiency.
2Reliability
If a metal-injecting layer containing small-work-function metal is formed to enhance electron injection, then electron-injection properties are improved, but the layer is decomposed and oxidized during sputtering process, leading to increased driving voltage and reduced device life
Solution Approach 1:
The patent forms the electron-injecting layer after depositing the light-transmissive cathode by sputtering, but before forming subsequent layers. By timing the formation of the metal-containing electron-injecting layer to occur after the sputtering process is complete, the metal component is protected from oxidation during sputtering, preventing degradation and maintaining device longevity.
Solution Approach 2:
The electron-injecting layer containing metal components is formed and maintained in an inert atmosphere (vacuum or nitrogen environment) throughout the deposition process. This inert environment prevents oxidation of the metal component, thereby preserving electron-injection properties and extending device life.
3Illumination intensity
If conventional electron-injecting layers are used with light-transmissive cathode, then light can be outcoupled, but driving voltage increases and luminous efficiency deteriorates
Solution Approach 1:
The patent optimizes the affinity level parameters of the electron-injecting layer to create a gradual transition from the cathode to the electron-transporting layer. By carefully selecting organic compounds and metal components with appropriate energy levels, the affinity level difference is minimized, reducing electron injection barriers and lowering driving voltage while maintaining light outcoupling 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
This configuration enhances luminous efficiency, prolongs device life, and allows for operation at lower voltages by stabilizing the electron transport process and preventing layer degradation, even when using ITO as a cathode.
Implementation Method 1
the acceptor-containing layer draws electrons from an interface with the cathode and transfers electrons into the donor-containing layer
Implementation Method 2
the donor-containing layer draws electrons from the acceptor-containing layer and injects them in the direction toward the emitting layer
Implementation Method 3
An organic electroluminescence (EL) device is a self-emission device utilizing the principle that light is emitted by the recombination energy of holes injected from an anode and electrons injected from a cathode
Data Source
Figure 1~2
AI summary
An organic electroluminescence device including: an anode; one or more organic thin film layers including an emitting layer; a donor-containing layer; an acceptor-containing layer; and a light-transmissive cathode in this order, wherein the donor-containing layer comprises a compound represented by the following formula (I) or (II):