OLED Emission Layer Energy Alignment for Carrier Balance
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Solution Overview
Problem
The existing light-emitting devices face issues with reduced luminous efficiency and shortened lifespan due to carrier injection and imbalance in organic layers between electrodes.
Innovation Solution
A light-emitting element configuration with specific energy level differences between layers, including a first and second hole transport layer, a light-emitting layer, and electron transport layers, optimized to efficiently transport carriers and reduce retention, enhancing luminous efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carriers are injected from each electrode into the organic layers between the electrodes, then the light-emitting device can operate, but the luminous efficiency reduces and lifespan shortens due to carrier retention and imbalance
Solution Approach 1:
The patent applies local quality by creating asymmetric energy level configurations at different interfaces of the light-emitting layer. Specifically, the energy level difference between the second hole transport layer and light-emitting layer is optimized to be greater than the energy level difference between the light-emitting layer and the electron transport layer, ensuring that carriers are efficiently extracted at each interface without accumulation. This localized optimization of energy level differences at different positions resolves the carrier imbalance problem while maintaining device operation.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the energy level differences (HOMO and LUMO levels) between adjacent layers. The configuration requires that the energy level difference between the second hole transport layer and light-emitting layer exceeds a threshold, and similarly for the electron transport layer interface. By adjusting these energy level parameters, the patent achieves efficient carrier extraction that prevents retention, thereby improving both luminous efficiency and device lifespan.
2Productivity
If the energy level differences between layers are optimized for efficient carrier transport, then luminous efficiency improves, but the device structure becomes more complex
Solution Approach 1:
The patent applies segmentation by dividing the charge transport function into distinct hole transport layers and electron transport layers with specific energy level characteristics. The device structure is segmented into a first hole transport layer, second hole transport layer, light-emitting layer, first electron transport layer, and second electron transport layer, each with optimized energy levels. This segmentation allows independent optimization of carrier transport at each interface, achieving high luminous efficiency through controlled carrier extraction without requiring overly 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
The optimized configuration improves carrier transport and reduces retention, leading to increased luminous efficiency and extended lifespan of the light-emitting device.
Implementation Method 1
a value of a LUMO level of the second hole transport layer is greater than a value of a LUMO level of the light-emitting layer on a side closer to the second hole transport layer, and a value of a LUMO level of the light-emitting layer on a side closer to the first electron transport layer is equal to or greater than a value of a LUMO level of the first electron transport layer
Implementation Method 2
an energy level difference between the second hole transport layer and the light-emitting layer on the side closer to the second hole transport layer is greater than an energy level difference between the light-emitting layer on the side closer to the second hole transport layer and a layer in contact with a side closer to the cathode electrode
Data Source
AI summary
In a light-emitting element, an energy level difference between a second hole transport layer and the light-emitting layer on a side closer to the second hole transport layer is greater than an energy level difference between the light-emitting layer on the side closer to the second hole transport layer and a layer in contact with a side closer to a cathode electrode of the light-emitting layer on the side closer to the second hole transport layer in LUMO level, and an energy level difference between a first electron transport layer and the light-emitting layer on a side closer to the first electron transport layer is greater than an energy level difference between the light-emitting layer on the side closer to the first electron transport layer and a layer in contact with a side closer to an anode electrode of the light-emitting layer on the side closer to the first electron transport layer in HOMO level.