Nanostructured OLED Emitter Layer for Light Outcoupling
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Solution Overview
Problem
In organic light-emitting diodes (OLEDs), a significant portion of generated light is lost due to wave guidance and surface plasmons, with only about a quarter being outcoupled, primarily due to the high refractive index of organic semiconductor materials leading to total reflection at interfaces with lower refractive index materials.
Innovation Solution
Incorporating nanostructures with a refractive index smaller than the light-emitting material into the organic layer sequence, where at least some nanostructures project into or pierce through the emitter layer, reducing the averaged refractive index and enhancing light outcoupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If organic semiconductor materials with high refractive index are used in OLEDs, then the materials can provide good charge transport properties, but light outcoupling efficiency deteriorates due to total reflection at interfaces
Solution Approach 1:
The patent introduces nanostructures with different refractive indices into the organic layer stack to change the effective refractive index parameter. By incorporating nanostructures with refractive indices between 1.3 and 1.7 (lower than the organic semiconductor material's refractive index of 1.8-2.0), the patent modifies the optical parameters of the device to reduce total reflection and improve light outcoupling efficiency while maintaining charge transport properties
Solution Approach 2:
The patent creates a composite structure by combining organic semiconductor materials with nanostructures made of different materials (such as metal oxides, nitrides, or other organic materials) with lower refractive indices. This composite approach allows simultaneous optimization of charge transport (provided by the organic material) and light outcoupling (enhanced by the low-refractive-index nanostructures)
2Loss of energy
If chemical modification is used to reduce the refractive index of organic semiconductor materials, then light outcoupling may improve, but material selection and device performance become limited
Solution Approach 1:
Instead of modifying the entire organic semiconductor material chemically, the patent segments the problem by introducing separate nanostructures with low refractive indices into the organic layer stack. This allows the organic semiconductor material to retain its original chemical structure and charge transport properties while the nanostructures independently provide the refractive index modification needed for improved light outcoupling
Solution Approach 2:
The patent uses nanostructures as intermediary elements between the organic semiconductor material and the surrounding media (substrate, electrode, encapsulation layers). These intermediary nanostructures with intermediate refractive indices (1.3-1.7) serve as optical mediators that reduce total reflection at interfaces without requiring chemical modification of the organic semiconductor material, thus preserving material selection flexibility
3Loss of energy
If only specific low refractive index materials are used in individual charge transport layers, then refractive index reduction is achieved, but the solution cannot be applied universally across all organic functional materials
Solution Approach 1:
The patent develops a universal solution by introducing nanostructures that can be integrated into any organic layer stack regardless of the specific organic functional materials used. The nanostructures serve multiple functions: they reduce total reflection at all interfaces (emitter layer/substrate, emitter layer/electrode, emitter layer/encapsulation), and they can be combined with any organic semiconductor material without requiring chemical modification, thus achieving both refractive index reduction and universal applicability
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 approach allows for more efficient light outcoupling, enabling the organic light-emitting device to produce an identical or higher light output with less input power, without the need for chemical modification of organic semiconductor materials, and can be applied universally across all organic functional materials.
Implementation Method 1
a major part of the light generated does not leave the organic layer stack due to total reflection at the interfaces with material layers with a lower refractive index
Implementation Method 2
The wave guidance effects arise in particular through the refractive index differences at the interfaces between the individual layers and regions of an OLED
Implementation Method 3
The rest of the light generated in the active region is distributed among various loss channels, for instance in light which is guided in the substrate, in a transparent electrode and in organic layers by wave guidance effects
Implementation Method 4
around 30% through the generation of surface plasmons in a metallic electrode
Data Source
AI summary
A light-emitting device includes a carrier, an organic layer sequence arranged on the carrier and having at least one emitter layer containing a light-emitting material configured to emit light of a first wavelength range, a first electrode and a second electrode, and a multiplicity of nanostructures, wherein the nanostructures have a refractive index smaller than a refractive index of the light-emitting material of the emitter layer and at least some of the nanostructures project into the emitter layer or pierce through the emitter layer.