OLED Optical Coupling-Out Layer for Plasmon Loss Reduction
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Solution Overview
Problem
Conventional organic light-emitting diodes (OLEDs) suffer from low light coupling efficiency due to waveguiding effects and surface plasmons, with only about a quarter of generated light being coupled out, while the rest is lost through substrates, transparent electrodes, and metallic electrodes, and existing solutions either have limited efficiency or alter the OLED's appearance.
Innovation Solution
An organic light-emitting component with a translucent electrode and reflective electrode, an organic functional layer stack, and an optical coupling-out layer with a high refractive index, strategically positioned to increase light coupling efficiency by reducing plasmon loss and enhancing waveguided light emission, with the organic light-emitting layer at a distance of at least 150 nm from the reflective electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If scattering films or surface structures are applied to the substrate to couple out light guided in the substrate, then the coupling-out efficiency is improved, but the appearance of the OLED is significantly influenced and becomes milky and diffusely reflective
Solution Approach 1:
The patent introduces an optical coupling-out layer with high refractive index (n≥1.6) as an intermediary between the substrate and the OLED structure. This layer couples out light guided in the substrate without producing the milky appearance of scattering films, thereby resolving the contradiction between improving light coupling efficiency and maintaining appearance quality
Solution Approach 2:
The patent changes the refractive index parameter of the optical coupling-out layer to be high (n≥1.6), which enables effective coupling out of light guided in the substrate while avoiding the appearance degradation associated with scattering structures. This parameter change allows simultaneous achievement of improved light extraction and maintained visual appearance
2Device complexity
If the organic light-emitting layer is positioned close to the reflective electrode, then the device structure is compact, but approximately 30% of generated light is lost as surface plasmons in the metallic electrode
Solution Approach 1:
The patent extracts the optical coupling-out function from the substrate interface and places it at the electrode interface through the optical coupling-out layer. This allows the organic light-emitting layer to remain close to the reflective electrode for structural compactness while the optical coupling-out layer prevents plasmon loss by coupling out light before it can generate surface plasmons
Solution Approach 2:
The patent converts the potentially harmful plasmon loss into beneficial light emission by positioning the optical coupling-out layer to intercept and couple out light that would otherwise be lost to surface plasmons in the metallic electrode, thereby transforming a loss mechanism into an emission enhancement mechanism
3Ease of manufacture
If conventional OLED structures are used, then the manufacturing process is simple, but only approximately one quarter of the generated light is coupled out into the surroundings
Solution Approach 1:
The optical coupling-out layer serves multiple functions simultaneously: it couples out light guided in the substrate, prevents plasmon loss in the metallic electrode, and enhances waveguided light emission. This multi-functionality improves light coupling efficiency from approximately 25% to significantly higher levels while adding minimal structural complexity to the manufacturing process
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 increases light coupling efficiency by reducing plasmon loss and enhancing waveguided light emission, allowing for higher light power emission through the substrate compared to conventional OLEDs, while maintaining a clear appearance.
Implementation Method 1
The waveguiding effects arise, in particular, as a result of the differences in refractive index at the interfaces between the individual layers and regions of an OLED
Implementation Method 2
The rest of the light generated in the active region is distributed among various loss channels, for instance in light guided in the substrate, in a transparent electrode and in organic layers as a result of waveguiding effects
Implementation Method 3
films comprising scattering particles, and films comprising surface structures such as microlenses, for instance, are used on the outer side of the substrate
Implementation Method 4
the translucent layer can be transparent, that is to say clearly translucent, or at least partly light-scattering and/or partly light-absorbing, such that the translucent layer can, for example, also be diffusely or milky translucent
Data Source
AI summary
An organic light-emitting component includes a substrate, on which are applied an optical coupling-out layer, a translucent electrode on the coupling-out layer, an organic hole-conducting layer or an organic electron-conducting layer on the translucent electrode, an organic light-emitting layer thereon, an organic electron-conducting layer or an organic hole-conducting layer on the organic light-emitting layer, and a reflective electrode. The organic light-emitting layer is at a distance of greater than or equal to 150 nm from the reflective electrode.