Light-Scattering Layer for OLED Light Extraction
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Solution Overview
Problem
Current OLED devices face inefficiencies in light output and lifetime due to trapped photons from internal reflection, and existing light extraction techniques either fail to extract all trapped light or compromise sharpness and durability.
Innovation Solution
A light-emitting LED device structure incorporating a light-scattering layer with encapsulating layers of varying refractive indices, where the light-scattering layer is positioned over the first encapsulating layer and an organic third transparent encapsulating layer with a lower refractive index is added between the scattering layer and the second encapsulating layer, enhancing light extraction and environmental protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a light-scattering layer is added to extract trapped light, then light output efficiency is improved, but device structure complexity increases
Solution Approach 1:
A light-scattering layer is introduced as an intermediary component between the organic light-emitting layers and the encapsulating layers. This scattering layer mediates the interaction between trapped photons and the device structure, enabling light extraction without requiring fundamental changes to the OLED architecture. The scattering layer acts as a buffer that converts guided modes into extractable light while maintaining compatibility with existing device layers.
Solution Approach 2:
The patent employs composite encapsulating layers with different refractive indices (first encapsulating layer with higher refractive index, second encapsulating layer with lower refractive index) combined with a light-scattering layer. This composite structure leverages the complementary properties of each material: the high-index layer provides strong light-trapping for efficiency, the scattering layer enables light extraction, and the low-index layer facilitates light outcoupling. Together, they form a synergistic system that resolves the contradiction between light extraction and structural simplicity.
2Adaptability or versatility
If color filters are used to create full-color display, then color variety is improved, but light absorption increases reducing efficiency
Solution Approach 1:
The patent converts the harmful effect of light absorption by color filters into a beneficial outcome. By positioning the light-scattering layer strategically and using multiple encapsulating layers with varying refractive indices, the device redirects light that would otherwise be absorbed by color filters. The scattering layer causes light to take multiple paths, increasing the probability that it will exit the device before being absorbed, thereby transforming the inevitable presence of color filters from a source of energy loss into a manageable component that can coexist with high light extraction efficiency.
3Reliability
If encapsulating layers are added to protect organic layers from environment, then reliability is improved, but light extraction efficiency deteriorates
Solution Approach 1:
The encapsulation system is segmented into multiple distinct layers with different optical properties. The first encapsulating layer (higher refractive index) provides primary environmental protection, the light-scattering layer handles light extraction, and the second encapsulating layer (lower refractive index) facilitates final light outcoupling. This segmentation allows each layer to specialize in its primary function without compromising the others, enabling simultaneous achievement of protection and light extraction efficiency.
Solution Approach 2:
Different regions of the encapsulation system are assigned different optical qualities. The first encapsulating layer has higher refractive index for strong light interaction and protection, while the second encapsulating layer has lower refractive index optimized for light outcoupling. The light-scattering layer is positioned specifically where it can intercept trapped light without interfering with the protective function of the encapsulating layers. This local differentiation of properties allows the system to simultaneously achieve environmental protection and high light extraction efficiency.
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 output, improves sharpness, and provides enhanced environmental protection by effectively scattering trapped light while maintaining the integrity of the light-emitting organic layers and reducing moisture permeation.
Implementation Method 1
a light-scattering layer with encapsulating layers of varying refractive indices, where the light-scattering layer is positioned over the first encapsulating layer
Implementation Method 2
encapsulating layers of varying refractive indices
Implementation Method 3
Due to the relatively high optical indices of the organic and transparent electrode materials used, most of the photons generated by the recombination process are actually trapped in the devices due to total internal reflection
Implementation Method 4
Light is generated in an LED device when electrons and holes that are injected from the cathode and anode, respectively, flow through the electron transport layer (ETL) and the hole transport layer (HTL) and recombine in the emissive layer
Data Source
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AI summary
A light-emitting LED device has one or more light-emitting LED elements (8), including first (12) and second (16) spaced-apart electrodes with one or more light-emitting layers (14) formed there-between, wherein at least one of the electrodes is a transparent electrode. Also included are a first transparent encapsulating layer (30) having a first optical index formed over the transparent electrode (16) opposite the light-emitting layer; a light-scattering layer (22) formed over the first transparent encapsulating layer opposite the transparent electrode; and a second transparent encapsulating layer (34), having a second optical index lower than the first optical index, formed over the light-scattering layer.