Multifunctional Optical Film for OLED Light Extraction
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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, leading to significant light loss, and existing solutions are either ineffective or incompatible with existing fabrication processes.
Innovation Solution
A multifunctional optical film with a flexible substrate, a structured layer of nanostructures, and a backfill layer with a contrasting refractive index, positioned within the evanescent zone to disrupt total internal reflection and enhance light extraction, while also providing mechanical support, barrier protection, and electrical conductance.
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 fabrication complexity and device reliability deteriorate due to the difficulty of creating defect-free interfaces
Solution Approach 1:
A separate light extraction film is introduced as an intermediary component between the OLED core and substrate. This film contains the scattering or diffractive elements (such as microlenses, prisms, or roughened surfaces) while maintaining a smooth interface with the OLED core. The intermediary film thus enables light extraction enhancement without compromising the reliability of the core device interface.
Solution Approach 2:
The light extraction function is segmented from the core OLED structure and placed in a separate film layer. This segmentation allows the light extraction elements to be optimized independently without affecting the fabrication and reliability of the core device, while still achieving the desired light extraction improvement.
2Loss of energy
If the core-to-substrate interface is disturbed with scattering or diffractive structures to enhance light extraction, then light extraction efficiency is improved, but ease of manufacture deteriorates due to the complexity of fabricating such structures
Solution Approach 1:
The light extraction film serves as an intermediary that can be manufactured separately using suitable techniques (such as molding or coating methods) and then integrated with the OLED device. This approach simplifies the overall manufacturing process compared to directly fabricating complex scattering structures at the core interface.
Solution Approach 2:
The light extraction film allows for optimization of geometric parameters (such as lens diameter, pitch, depth, or surface roughness) without changing the fundamental fabrication process of the core OLED device. These parameter changes can be achieved through standard manufacturing techniques applied to the separate film layer.
3Loss of energy
If microlenses or roughened surfaces are used to disturb the substrate-to-air interface, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The light extraction film is designed to be a universal component that can be applied to various OLED device types and configurations. By consolidating the light extraction function in a single multi-functional film layer, the overall device complexity is managed more effectively than if multiple separate components were required.
Solution Approach 2:
Multiple functions (light extraction enhancement, interface smoothing, and potential encapsulation or protection) are merged into a single light extraction film component. This consolidation reduces the number of separate parts and simplifies the overall device structure while achieving the desired light extraction improvement.
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 improves light extraction efficiency by up to 100% compared to unmodified OLED devices, maintaining the electrical and optical integrity of the OLEDs and being compatible with existing fabrication processes.
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
a substantial portion of the extraction elements are within an evanescent zone adjacent to a light emitting region of a self-emissive light source
Implementation Method 3
The backfill layer has a material having a second index of refraction different from the first index of refraction
Implementation Method 4
When a voltage is applied across the device, electrons and holes are injected from their respective electrodes and recombine in the electroluminescent organic material through the intermediate formation of emissive excitons
Data Source
AI summary
A multifunctional optical film for enhancing light extraction includes a flexible substrate, a structured layer, 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 lighting device such as solid state lighting devices or backlight units. 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.