Multi-Emission OLED Layer Stack for Balanced Charge Injection
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Solution Overview
Problem
Multi-emission-layer organic light-emitting diodes (OLEDs) face challenges in improving their lifetime and efficiency, particularly in top emission configurations, where the balance of hole and electron injection is crucial for optimal performance.
Innovation Solution
The OLED design incorporates a specific stack structure including a first emission layer, a second emission layer, a first charge generation layer, and a first electron transport layer stack, where the first electron transport layer comprises a compound of Formula (I) and the second electron transport layer comprises a compound of Formula (II), both without electrical dopants, and the first charge generation layer uses the same compound as the second electron transport layer, optimizing the dipole moment and layer arrangement for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multi-emission-layer structure is used to improve device functionality, then the versatility and performance are enhanced, but the lifetime and efficiency deteriorate due to unbalanced charge injection
Solution Approach 1:
A charge generation layer is introduced as an intermediary component between the emission layers to mediate charge balance. This layer generates both holes and electrons that are injected into adjacent emission layers, ensuring balanced charge injection without requiring separate charge injection electrodes for each layer, thus improving lifetime while maintaining multi-emission functionality
Solution Approach 2:
Different electron transport materials with specific dipole moments are used in different regions (first vs. second electron transport layer) to optimize local charge transport properties. The first electron transport layer uses a material with a higher dipole moment than the second electron transport layer, creating localized electric field gradients that facilitate balanced charge injection into multiple emission layers
2Productivity
If multiple electron transport layers are stacked to improve charge balance, then the efficiency is enhanced, but the device complexity increases
Solution Approach 1:
The charge generation layer serves multiple functions simultaneously: it generates holes for injection into the first emission layer, generates electrons for injection into the second emission layer, and provides a simplified interface that reduces the need for additional charge injection electrodes. This multi-functionality improves charge transport efficiency without proportionally increasing device complexity
Solution Approach 2:
The dipole moment parameter of electron transport materials is strategically varied between layers (first electron transport layer has higher dipole moment than second), creating optimized electric field distributions that enhance charge transport efficiency across the multi-layer structure without requiring complex additional components
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 the lifetime and efficiency of the OLED by balancing charge injection and transport, leading to improved performance and reduced operating voltage, specifically in multi-emission-layer top emission OLEDs.
Implementation Method 1
the first electron transport layer comprises a compound of Formula (I) and the second electron transport layer comprises a compound of Formula (II)
Implementation Method 2
the first charge generation layer uses the same compound as the second electron transport layer, optimizing the dipole moment and layer arrangement for improved performance
Implementation Method 3
The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
Data Source
Figure 1
Figure 2A~2C
AI summary
The present invention relates to an organic light emitting diode comprising an anode, a cathode, a first emission layer, a second emission layer, a first charge generation layer and a first electron transport layer stack; and to a display device or lighting device comprising the same.