Organic EL Layer Structure for High Light Extraction
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Solution Overview
Problem
In organic electroluminescence display devices, achieving high light extraction efficiency while maintaining a long device lifetime is challenging due to restrictions on the film thickness of the organic EL layer, which limits the selection of the light emitting position and increases drive voltage when attempting to enhance electron mobility.
Innovation Solution
The use of a specific organic layer structure with a hole injecting layer, hole transporting layer, electron blocking layer, light emitting layer, hole blocking layer, and electron transporting layer, where the electron transporting layer includes an alkali metal or alkaline earth metal like lithium, allowing for improved electron mobility and optimized layer thicknesses to enhance light extraction efficiency without increasing drive voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a larger voltage is applied to increase current density for higher luminance, then light emission intensity is improved, but device lifetime is shortened
Solution Approach 1:
The patent changes the optical parameters of the device by introducing a micro-cavity structure with specific resonance conditions. This allows the device to achieve high luminance through optical resonance amplification rather than increasing current density, thereby maintaining device lifetime while improving illumination intensity.
2Loss of energy
If optical resonance structure is applied to improve light extraction efficiency, then light extraction is enhanced, but the selection of light emitting position is restricted due to film thickness constraints
Solution Approach 1:
The patent introduces a vertical micro-cavity structure that creates optical resonance in the thickness direction. This dimensional approach allows independent optimization of the optical path without being constrained by the lateral positioning of the light emitting layer, thereby maintaining flexibility in light emitting position selection while achieving high light extraction efficiency.
3Reliability
If electron transporting layer thickness is increased to improve electron mobility, then carrier transport is enhanced, but drive voltage increases
Solution Approach 1:
The patent optimizes the thickness parameter of the electron transporting layer to achieve the best balance between electron mobility and drive voltage. By precisely controlling the layer thickness within a specific range, the device achieves high carrier transport efficiency without excessive voltage requirements.
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 improves light extraction efficiency and maintains a lower drive voltage by balancing carrier mobility and layer thickness, resulting in enhanced performance and longevity of the light emitting device.
Implementation Method 1
a fifth organic layer having an electron transporting property arranged on the fourth organic layer, wherein the fifth organic layer includes an alkali metal or an alkaline earth metal such as calcium or lithium
Implementation Method 2
the light emitting position of the organic EL layer between the semi-reflecting surface and the total reflecting surface greatly influences the light extraction efficiency
Implementation Method 3
Japanese Unexamined Patent Application Publication No. 2005-116516 discloses a method of resonating light between a total reflection surface on the anode side and a semi-reflecting surface on the cathode
Implementation Method 4
The reflected light is transmitted through the organic layer and the anode, and is reflected on the total reflection surface
Implementation Method 5
When a potential is applied to the electrode of the light emitting device, electrons are injected from the cathode and holes are injected from the anode. The electrons and the holes move in the organic layer, recombine with the host molecule of the light emitting layer and release energy. As a result, the luminescent molecules in the light emitting layer are excited by the energy released thereby, and then the luminescent molecules return to the ground state to emit light
Data Source
AI summary
A light emitting device includes a pixel electrode, an organic layer, and a counter electrode, wherein the organic layer includes a first organic layer having a hole injecting property, a second organic layer having a hole transporting property, a third organic layer having an electron blocking property, a light emitting layer containing a host material and a dopant material, a fourth organic layer having a hole blocking property, and a fifth organic layer having an electron transporting property, wherein the fifth organic layer includes an alkali metal such as calcium or lithium and the like or an alkaline earth metal, and a total layer thickness of the first organic layer, the second organic layer, and the third organic layer is smaller than a total layer thickness of the fourth organic layer and the fifth organic layer.