Alternating Hole Injection and Transport Layers in OLEDs
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Solution Overview
Problem
In conventional organic light emitting devices, insufficient hole injection from the anode into the hole transport layer results in high driving voltage and reduced efficiency, leading to decreased lifespan due to hole accumulation at the anode interface.
Innovation Solution
The configuration of the organic light emitting device is modified by incorporating a hole transport unit with alternating layers of a single hole injection material and a single hole transport material, where the LUMO level of the hole injection layers is lower than the HOMO level of the hole transport layers by 0.01 eV to 1.00 eV, facilitating efficient hole injection and reducing interfacial barriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-layer hole transport structure is used, then the device structure is simple, but hole injection efficiency is insufficient leading to high driving voltage
Solution Approach 1:
The hole transport layer is segmented into multiple sub-layers with different functions: a hole injection layer adjacent to the anode for efficient hole injection, and a hole transport layer for charge transport. This segmentation allows optimization of each layer's properties to reduce the overall driving voltage while maintaining structural complexity at an acceptable level.
Solution Approach 2:
Different regions of the hole transport structure are assigned different material properties and thicknesses. The hole injection layer has specific LUMO/HOMO levels optimized for anode interface charge transfer, while the hole transport layer has properties optimized for charge mobility. This local quality differentiation enables efficient hole injection without requiring complex overall structure.
2Ease of manufacture
If a conventional single-layer hole transport structure is used, then the manufacturing process is simple, but hole injection efficiency is insufficient leading to reduced device lifespan
Solution Approach 1:
The hole transport function is segmented into injection and transport sub-functions implemented by separate layers. This segmentation prevents hole accumulation at the anode interface by providing dedicated injection pathways, thereby extending device lifespan while maintaining relatively simple fabrication processes for each individual layer.
Solution Approach 2:
The hole injection layer acts as an intermediary between the anode and the hole transport layer, facilitating efficient charge transfer and preventing direct harmful interactions at the interface. This intermediary layer protects the device from degradation while keeping the manufacturing process straightforward.
3Device complexity
If the LUMO level of hole injection layer is not lower than HOMO level of hole transport layer, then the energy alignment is simpler, but hole injection efficiency is insufficient
Solution Approach 1:
The energy level parameters (LUMO and HOMO levels) of the hole injection layer are specifically adjusted to create a favorable energy gradient. By ensuring the LUMO level is lower than the HOMO level of the adjacent hole transport layer, the patent optimizes the energy alignment parameter to drive efficient hole injection from the anode through the injection layer into the transport layer, improving productivity without excessive complexity.
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 hole injection efficiency, lowers driving voltage, and significantly extends the lifespan of the organic light emitting device by preventing performance degradation and maintaining chemical stability of the layers.
Implementation Method 1
the LUMO level of the hole injection layers is lower than the HOMO level of the hole transport layers by 0.01 eV to 1.00 eV, facilitating efficient hole injection and reducing interfacial barriers
Implementation Method 2
Holes and electrons from the anode and cathode are injected into the organic light emitting layer and are combined with each other in the organic light emitting layer, thus generating excitons. When the generated excitons are changed from an excited state to a ground state, the organic light emitting device emits light.
Data Source
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AI summary
Disclosed are an organic light emitting device and an organic light emitting display using the same. The organic light emitting device includes two or more pairs of hole injection layers (210a, 210b, ...) formed of a single material and hole transport layers (220a, 220b, ...) formed of a single material, being alternately stacked, thereby achieving reduction in driving voltage and improvement in efficiency and lifespan.