OLED Light Extraction via Auxiliary Electrode Grid and Scattering Layer
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Solution Overview
Problem
OLED devices face inefficiencies in light output due to trapped photons from internal reflection, and existing solutions fail to effectively extract light while maintaining robustness and reducing manufacturing costs.
Innovation Solution
An OLED device structure incorporating a substrate, organic light-emitting layers, a transparent second electrode, a light scattering layer between the substrate and cover, and an auxiliary electrode grid forming transparent gaps with a lower refractive index to scatter and extract light, thereby reducing internal reflections and enhancing mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a typical OLED device structure with glass substrate, transparent conducting anode, organic layers, and reflective cathode is used, then the device can generate light through electron-hole recombination, but nearly 60% of generated light is trapped by internal reflection in the ITO/organic EL element, 20% is trapped in the glass substrate, and only about 20% is actually emitted
Solution Approach 1:
The patent introduces an intermediary layer with intermediate refractive index between the high-index organic/ITO layers and the low-index air/encapsulant. This intermediate layer acts as a mediator that gradually transitions the refractive index, reducing the abrupt index mismatch that causes total internal reflection. The intermediary layer enables photons to escape from the waveguide modes by providing a step-wise refractive index transition path.
Solution Approach 2:
The patent changes the refractive index parameter by introducing layers with specifically engineered refractive indices between the high-index organic/ITO layers and the low-index encapsulant. By adjusting the refractive index parameter of the intermediate layers, the patent optimizes light extraction efficiency while maintaining electrical performance. This parameter change approach directly addresses the optical confinement problem.
2Strength
If the encapsulating cover is affixed directly to the substrate without sufficient spacing, then the device structure is compact, but the thin-film layers may contact the cover causing damage and reduced device robustness
Solution Approach 1:
The patent segments the device structure by introducing auxiliary electrodes that extend from the substrate through the organic layers to the encapsulating cover. These auxiliary electrodes create discrete spacing regions that prevent direct contact between the cover and sensitive thin-film layers. The segmentation approach divides the device into functional zones with appropriate spacing, enhancing robustness without requiring a completely redesigned structure.
Solution Approach 2:
The auxiliary electrodes serve multiple functions: they provide electrical connections for the OLED, create mechanical spacing to prevent cover contact, and can serve as structural support elements. This multi-functionality allows the same structural element to address both electrical and mechanical requirements, adding robustness without proportionally increasing complexity.
3Illumination intensity
If transparent electrode materials such as ITO are used, then the electrode can transmit light, but these materials have low conductivity which results in voltage drop, resistive heating, and power loss
Solution Approach 1:
The patent employs composite electrode structures combining transparent conductive oxide layers (like ITO) with metal layers or conductive polymer layers. This composite approach leverages the high transparency of TCOs and the high conductivity of metals/polymers, creating an electrode that achieves both light transmission and low electrical resistance. The composite material strategy resolves the trade-off between optical and electrical properties.
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
Improves light extraction efficiency and robustness of OLED devices while reducing manufacturing costs by minimizing internal reflections and maintaining mechanical integrity.
Implementation Method 1
a light scattering layer located between the substrate and cover for scattering light emitted by the light-emitting layer
Implementation Method 2
forming transparent gaps between the transparent second electrode and the cover within grid openings, the transparent gaps having a third refractive index lower than each of the first refractive index range and second refractive index
Data Source
AI summary
An organic light-emitting diode (OLED) device, comprising: a substrate; an OLED formed on the substrate comprising a first electrode, one or more layers of organic material, one of which emits light, and a transparent second electrode formed over the one or more layers of organic material, the transparent second electrode and layer(s) of organic light-emitting material having a first refractive index range; a transparent cover having a second refractive index; a light scattering layer located between the substrate and cover for scattering light emitted by the light-emitting layer; and an auxiliary electrode grid located above the transparent second electrode, providing spacing between the transparent second electrode and the cover, and forming transparent gaps between the transparent second electrode and the cover within grid openings, the transparent gaps having a third refractive index lower than each of the first refractive index range and second refractive index.