OLED Light Extraction Grating Structure for Outcoupling Efficiency
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Solution Overview
Problem
Conventional organic light-emitting diodes (OLEDs) suffer from low outcoupling efficiency, with only 20-30% of generated light being emitted externally, due to light being trapped in substrate, waveguided, and surface plasmon modes, primarily due to refractive index mismatches between layers.
Innovation Solution
Incorporating a light extraction layer between the substrate and the first electrode with a grating structure, which increases the refractive index difference and promotes the extraction of waveguided and surface plasmon modes into the substrate mode, enhancing outcoupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional planar OLED structure is used, then the device structure is simple and easy to manufacture, but the outcoupling efficiency is low with only 20-30% of generated light being emitted externally
Solution Approach 1:
A light extraction layer is introduced as an intermediary component between the substrate and the first electrode. This layer has a refractive index specifically positioned between that of the substrate and the electrode, creating favorable refractive index gradients that reduce total internal reflection and enhance light extraction efficiency from the OLED device
Solution Approach 2:
A grating structure is incorporated at the interface between the light extraction layer and the first electrode. This introduces a periodic micro-structure dimension that enables diffraction of waveguided modes and surface plasmon modes into extractable substrate modes, significantly enhancing light outcoupling beyond what a planar structure could achieve
2Loss of energy
If the refractive index difference between layers is increased to extract waveguided and surface plasmon modes, then the outcoupling efficiency improves, but the device complexity increases due to the additional light extraction layer and grating structure
Solution Approach 1:
The light extraction layer serves multiple functions simultaneously: it acts as a refractive index mediator to reduce total internal reflection, provides a platform for the grating structure to enable mode conversion, and maintains electrical insulation between the substrate and electrode. This multi-functionality justifies the additional layer despite the increase in device complexity
3Productivity
If a light extraction layer with grating structure is incorporated to enhance outcoupling, then the external quantum efficiency increases to up to 67%, but the manufacturing process becomes more complex
Solution Approach 1:
The grating structure is formed on the substrate surface before depositing the light extraction layer and subsequent OLED layers. This preliminary formation of the grating pattern enables subsequent layers to be deposited conformally, simplifying the overall manufacturing process compared to attempting to form gratings on pre-assembled OLED structures
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 increases the outcoupling efficiency of OLEDs, achieving up to 67% external quantum efficiency and 210 cd/A current efficiency by effectively extracting trapped light, particularly from the waveguided mode, while maintaining device operability.
Implementation Method 1
a first interface between the light extraction layer and the first electrode comprises a first grating structure
Implementation Method 2
a difference between a refractive index of the light extraction layer and a refractive index of the first electrode has a magnitude of at least 0.20
Data Source
AI summary
Embodiments described herein generally relate to organic light-emitting diodes (OLEDs) comprising a substrate, a light extraction layer, a first electrode, one or more organic layers, and a second electrode. In some embodiments, the light extraction layer is positioned between the substrate and the first electrode. According to some embodiments, an interface between the light extraction layer and the first electrode comprises a grating structure. The grating structure may, in certain cases, promote outcoupling of light generated within the OLED (e.g., through diffraction).