OLED Electron Transport Layer Refractive Index Optimization
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Solution Overview
Problem
Current organic electroluminescent devices suffer from low light out-coupling efficiency, with only 20% of generated light being coupled out, due to total reflection at the surfaces between organic layers and the substrate, leading to trapped light within the glass substrate and organic layers.
Innovation Solution
Incorporating an electron transport layer with a refractive index between 1.3 and 1.65, combined with n-doped layers, to reduce light reflection and enhance light out-coupling, along with a charge generation layer stack to improve charge injection and separation, allowing more light to be coupled out of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional organic electroluminescent device structure is used, then device simplicity is maintained, but light out-coupling efficiency is poor with only 20% of light being coupled out
Solution Approach 1:
The patent introduces an electron transport layer with specific refractive index (1.3-1.65) as an intermediary between the organic light emitting layer and the electrode. This intermediate layer acts as an optical mediator that reduces total internal reflection at interfaces, enabling more light to escape the device while maintaining electrical functionality.
Solution Approach 2:
The patent changes the refractive index parameter of the electron transport layer to a specific range (1.3-1.65) that is optimized for light out-coupling. By adjusting this optical parameter, the device achieves improved light extraction efficiency without fundamentally changing the overall device architecture.
2Loss of energy
If electron transport layer with low refractive index is added, then light out-coupling is improved, but device complexity increases
Solution Approach 1:
The electron transport layer performs multiple functions simultaneously: it transports electrons (electrical function) and manages light extraction (optical function) through its specific refractive index. This multi-functionality allows the layer to improve light out-coupling without adding separate dedicated optical components.
Solution Approach 2:
By optimizing the refractive index parameter within the range of 1.3-1.65, the patent achieves effective light out-coupling enhancement while keeping the layer thickness and material composition within practical manufacturing limits, avoiding excessive device complexity.
3Reliability
If n-doped layers are incorporated, then charge injection and separation are improved, but manufacturing complexity increases
Solution Approach 1:
The patent introduces doping as a parameter change to the electron transport layer, adding n-type dopants to improve charge injection and separation. This chemical parameter modification enhances electrical performance while using standard doping techniques compatible with existing OLED manufacturing processes.
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 solution significantly improves light out-coupling, increasing the amount of light emitted from the device, resulting in enhanced brightness and efficiency at specific driving voltages, while maintaining stability and longevity.
Implementation Method 1
an electron transport layer made of a first electron transport material having a refractive index between 1.3 and 1.65
Implementation Method 2
Due to the optical properties of the organic layers and the transparent substrate and resulting total reflection at the surfaces between organic layers and substrate as well as between substrate and air
Implementation Method 3
a first charge generation layer stack arranged between the first electrode and the organic light-emitting layer stack, wherein the first charge generation layer stack comprise at least a n-doped layer facing towards the first electrode
Implementation Method 4
the first charge generation layer stack comprise at least a n-doped layer facing towards the first electrode and a p-doped layer facing towards the organic light-emitting layer stack
Implementation Method 5
organic molecules emit light when a driving voltage is applied to such organic electroluminescent devices
Data Source
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AI summary
The invention provides an OLED device with improved light out-coupling comprising an electroluminescent layer stack (2) on top of a substrate(1), where the electroluminescent layer stack (2) comprises an organic light-emitting layer stack (6) with one or more organic layers sandwiched between a first electrode (3) facing towards the substrate (1) and a second electrode(7) to apply a driving voltage to the organic light- emitting layer stack (6), and a first electron transport layer stack (4a) arranged between the organic light emitting layers stack (6) and the second electrode (7), wherein the electron transport layer stack (4a) comprises an electron transport layer (41) made of a first electron transport material having a low refractive index and at least one n-doped layer (40, 42). The invention further relates to a method to manufacture these OLED devices.