Optical Coupling Layer with High Index Nanoparticles for OLED Light Extraction
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Solution Overview
Problem
In OLED devices, over 70% of generated light is lost due to internal reflections and trapping at the interfaces between higher index organic and indium tin oxide (ITO) layers and lower index substrate layers, resulting in poor light extraction efficiency.
Innovation Solution
A method involving an optical film with an optical coupling layer comprising at least 40 wt.-% inorganic nanoparticles having a refractive index of at least 1.85 and a polymeric silane surface treatment, applied to the surface of the optical film or substrate, enhancing light extraction by laminating the optical film to the substrate, forming a laminated optical construction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional OLED device structure is used, then device simplicity is maintained, but light extraction efficiency deteriorates with over 70% light loss
Solution Approach 1:
The patent introduces an optical coupling layer as an intermediary component between the OLED device and optical film. This layer contains surface-modified high index nanoparticles (with refractive index ≥1.85) that serve as a mediator to improve optical coupling and reduce internal reflections, thereby increasing light extraction efficiency without fundamentally redesigning the OLED structure
Solution Approach 2:
The optical coupling layer is formulated as a composite material system combining inorganic high index nanoparticles with organic binder materials. The nanoparticles (such as TiO2, ZrO2, or SiO2) provide high refractive index for improved light extraction, while the binder matrix provides structural integrity and adhesion, creating a composite that simultaneously addresses optical performance and manufacturing requirements
2Loss of energy
If optical coupling layer with high index nanoparticles is applied, then light extraction efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The nanoparticles are pre-modified with surface treatments (such as silane, oxide, or organic monolayer coatings) before being incorporated into the optical coupling layer. This preliminary surface modification ensures proper dispersion, adhesion, and optical properties, simplifying the subsequent manufacturing process by eliminating the need for complex in-situ modification steps
Solution Approach 2:
The patent optimizes the refractive index parameter of the nanoparticles (≥1.85) and their concentration in the optical coupling layer to achieve effective light extraction enhancement. By carefully controlling these parameters, the patent achieves improved optical performance while maintaining manufacturability through standard coating and curing processes
3Loss of energy
If internal reflections at interfaces are reduced, then usable light output increases, but light distribution control becomes more challenging
Solution Approach 1:
The optical coupling layer is applied locally at specific interfaces within the OLED device structure, particularly at the boundary between the OLED device and the optical film. This localized application targets the specific interface where internal reflections occur most significantly, improving light extraction where needed while maintaining control over overall light distribution
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
Significantly improves light extraction efficiency by reducing internal reflections and enhancing the angular distribution of light, allowing more light to be emitted from the OLED device, thereby increasing the usable light output.
Implementation Method 1
The trapping of light at the interfaces between the higher index organic and indium tin oxide (ITO) layers and the lower index substrate layers is the major cause of this poor extraction efficiency
Implementation Method 2
Over 70% of the generated light is typically lost due to processes within the device structure, including internal reflections
Data Source
AI summary
Presently described is a method for coupling an optical film to a substrate, laminated optical constructions comprising an optical film and an optical coupling layer disposed on a surface layer of the optical film, and coating compositions useful for optical an optical coupling layer. The coating compositions comprise at least 40 wt.-% inorganic nanoparticles having a refractive index of at least 1.85 and a polymeric silane surface treatment.