Organic Electroluminescence Element with Segmented Light-Emitting Layers
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Solution Overview
Problem
Existing organic electroluminescence elements face challenges in achieving high external quantum efficiency and driving durability, with previous solutions either compromising brightness or increasing driving voltage, and existing multi-layer structures fail to effectively utilize light emission from individual units.
Innovation Solution
The organic electroluminescence element is designed with a light-emitting layer divided into multiple thin layers, each containing a light-emitting material and a host material, with intermediate layers acting as electron or hole blocking materials, where the electron affinity or ionization potential differences between these layers are carefully controlled to enhance charge blocking and recombination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an interface layer is disposed between the light emitting layer and hole transport layer to control carrier migration balance, then external quantum efficiency is enhanced, but brightness is lowered and driving voltage is increased
Solution Approach 1:
The light emitting layer is divided into multiple sub-layers (first light emitting layer, second light emitting layer, etc.) with different host materials and luminescent dopants. This segmentation allows each sub-layer to have optimized carrier transport properties, preventing the need for a blocking interface layer while maintaining high external quantum efficiency. The segmented structure enables gradual carrier migration control without creating sharp barriers that would reduce brightness.
Solution Approach 2:
Different regions of the light emitting layer are assigned different local properties through the use of various host materials (e.g., mCP, TCTA, TAPC) and luminescent dopants in different sub-layers. Each local region is optimized for specific functions: some regions favor electron transport, others favor hole transport, creating a balanced carrier distribution throughout the layer without requiring additional interface layers.
2Loss of energy
If an interface layer is disposed between the light emitting layer and hole transport layer to control carrier migration balance, then external quantum efficiency is enhanced, but driving durability is lowered
Solution Approach 1:
The light emitting layer is segmented into multiple sub-layers that progressively control carrier migration. This eliminates the need for a separate interface layer that would extend carrier residence time, thereby preventing degradation while maintaining high external quantum efficiency through optimized local carrier balance in each sub-layer.
3Device complexity
If light emitting units are stacked in multi-layer structure with insulation layers, then device complexity is reduced, but light extraction is hindered and external quantum efficiency is not improved
Solution Approach 1:
Multiple light emitting units are merged into a single integrated light emitting layer structure with continuous carrier transport pathways. The first, second, and subsequent light emitting layers are connected through optimized interface designs that allow efficient carrier migration between layers without requiring insulating barriers, enabling both structural simplicity and high light extraction efficiency.
Solution Approach 2:
The patent introduces intermediate host materials and charge transport materials at the interfaces between light emitting sub-layers to mediate carrier transfer. These intermediary materials facilitate smooth carrier migration between layers with different properties, eliminating the need for insulating layers while maintaining device simplicity and enhancing external quantum efficiency through improved carrier distribution.
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 significantly improves external quantum efficiency and driving durability by optimizing charge blocking and light extraction, while maintaining efficient carrier recombination and reducing driving resistance.
Implementation Method 1
The organic electroluminescence element is a device for obtaining luminescence by utilizing at least either one of luminescence from excitons each of which is obtained by recombining an electron injected from a cathode with a hole injected from an anode to produce the exciton
Implementation Method 2
an Ea (electron affinity) value of the electron blocking material contained in the intermediate layer adjacent on an anode side of the light-emitting layer is smaller than an Ea value of a host material contained in the light-emitting layer
Implementation Method 3
an Ip (ionization potential) value of the hole blocking material contained in the intermediate layer adjacent on a cathode side of the light-emitting layer is larger than an Ip value of a host material contained in the light-emitting layer
Data Source
AI summary
An organic electroluminescence element includes at least a light-emitting layer between a pair of electrodes, wherein the light-emitting layer is divided into at least three layers, an intermediate layer containing an electron blocking material or a hole blocking material is disposed between the divided light-emitting layers, an Ea value of the electron blocking material is smaller than an Ea value of a host material of the divided light-emitting layer adjacent on a cathode side or an Ip value of the hole blocking material is larger than an Ip value of a host material of the divided light-emitting layer adjacent on the anode side of the intermediate layer, and a difference of ΔEa or ΔIp is controlled to specific range.