Nanoparticle Coated Light Extraction Film for OLEDs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Organic Light Emitting Diodes (OLEDs) suffer from low light extraction efficiency due to internal reflections at interfaces between high and low index layers, with existing solutions being either ineffective or incompatible with existing fabrication processes.
Innovation Solution
A multifunctional optical film with a flexible substrate, structured layer, and backfill layer, featuring nanoparticles of different sizes to create a nanostructured surface that disrupts total internal reflection and enhances light extraction by providing index contrast and planarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If scattering or diffractive elements are introduced at the core-to-substrate interface to improve light extraction, then light extraction efficiency is improved, but the surface becomes non-planar making fabrication difficult
Solution Approach 1:
The light extraction function is segmented from the substrate surface and transferred to discrete scattering elements (nanoparticles, microlenses, or roughened regions) that are applied as a separate layer or coating on the planar substrate. This allows the substrate to remain planar for fabrication while the scattering elements provide the light extraction function.
Solution Approach 2:
A separate scattering element layer is introduced as an intermediary between the substrate and the OLED device. This intermediary layer provides the light extraction function through scattering or diffraction while the underlying substrate maintains its planar surface for easy fabrication.
2Loss of energy
If the substrate surface is corrugated to couple light out of the OLED, then light extraction is improved, but the electric fields in the device are adversely affected
Solution Approach 1:
The light extraction function is separated from the substrate surface and implemented through discrete scattering elements that can be applied as a coating or layer. This segmentation allows the substrate to remain electrically inert while the scattering elements provide optical function without interfering with electrical fields.
Solution Approach 2:
A scattering element layer serves as an intermediary that provides light extraction functionality without directly contacting or interfering with the OLED's electrical components. The scattering elements are positioned and designed to be optically active but electrically passive.
3Loss of energy
If scattering elements are introduced into the substrate or adhesive to redirect light, then light extraction is improved, but the fabrication process becomes more complex
Solution Approach 1:
The scattering function is extracted from the substrate or adhesive matrix and implemented as separate, discrete scattering elements that can be applied as a surface coating or layer. This simplifies fabrication by allowing the substrate and adhesive to be manufactured using standard processes, with the scattering function added separately.
Solution Approach 2:
The scattering elements are implemented as a separate coating or layer that can be applied using simple, low-cost techniques such as spin-coating, dip-coating, or lamination. This approach is more fabrication-friendly than incorporating scattering elements into the substrate or adhesive, which would require complex manufacturing steps.
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 locating nanostructured index contrast layers within the evanescent zone, allowing trapped light to escape and enhancing the overall performance of OLED devices without adverse effects on electrical operation.
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
Scattering efficiency is maximized when the index contrast between the scattering or diffractive elements and the backfill material is large and when the length scale of the index contrast variations is comparable to the wavelength of the light
Implementation Method 3
Detailed analysis has shown that scattering or diffractive structures will be most effective in extraction light when located at this interface
Data Source
AI summary
A multifunctional optical film for enhancing light extraction includes a flexible substrate, a structured layer having nanoparticles of different sizes, and a backfill layer. The structured layer effectively uses microreplicated diffractive or scattering nanostructures located near enough to the light generation region to enable extraction of an evanescent wave from an organic light emitting diode (OLED) device. The backfill layer has a material having an index of refraction different from the index of refraction of the structured layer. The backfill layer also provides a planarizing layer over the structured layer in order to conform the light extraction film to a layer of an OLED display device. The film may have additional layers added to or incorporated within it to an emissive surface in order to effect additional functionalities beyond improvement of light extraction efficiency.