Polycycloolefin Optical Films for OLED Refractive Index Matching
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Solution Overview
Problem
Conventional OLEDs face challenges with refractive index mismatch between organic layers and glass substrates, leading to photon loss, and require protective materials that are stable, transparent, and compatible with fabrication processes.
Innovation Solution
A single component mass polymerizable polycycloolefin monomer composition comprising norbornene-based monomers with a refractive index of 1.4 to 1.6, which undergoes polymerization at elevated temperatures or radiation, forming a transparent optical layer with adhesion to both OLED stacks and glass covers, and exhibits low viscosity and shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional OLED structures are used with glass substrates, then device assembly is simple, but light extraction efficiency is low due to refractive index mismatch
Solution Approach 1:
The patent introduces an intermediate layer composed of polycycloolefin polymer (norbornene-based) with refractive index n=1.7-1.9 that matches the organic light-emitting layer. This intermediary layer serves as a refractive index bridge between the organic layer (n=1.7-1.9) and the glass substrate (n=1.5), enabling efficient light extraction while maintaining simple device assembly. The intermediate layer is applied as a coating on the glass substrate before OLED assembly.
2Reliability
If protective coating materials are applied to protect OLEDs from harsh conditions, then OLED reliability improves, but fabrication process complexity increases
Solution Approach 1:
The patent combines multiple functions into a single protective coating layer: (1) barrier function against moisture and oxygen, (2) refractive index matching for light extraction, and (3) thermal stability for fabrication process compatibility. The polycycloolefin polymer provides all these functions simultaneously, eliminating the need for separate protective layers and simplifying the fabrication process.
Solution Approach 2:
The patent utilizes the thermal and optical parameters of the polycycloolefin polymer to enable in-situ polymerization during OLED fabrication. The monomer form is applied as a low-viscosity coating, then polymerized in-place using thermal or UV irradiation, transforming from a processable liquid to a protective solid layer without requiring additional fabrication steps.
3Ease of operation
If single component mass polymerizable composition is used, then dispensing and application is simplified, but control over polymerization timing becomes difficult
Solution Approach 1:
The patent incorporates a photoinitiator or thermal initiator into the single-component monomer composition during manufacturing. This preliminary action enables controlled polymerization to be triggered later during OLED fabrication using UV irradiation or thermal processing, allowing the composition to remain stable and dispensable in monomer form while enabling on-demand polymerization.
Solution Approach 2:
The patent exploits the phase transition from monomer to polymer, and from liquid to solid, to control the timing and properties of the protective layer. The monomer is applied in liquid form for easy dispensing, then undergoes phase transition to solid polymer during fabrication, providing both ease of application and controlled final properties.
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 composition enhances light extraction into substrates, provides stable protection against harsh conditions, and facilitates rapid polymerization, forming a uniform, transparent film with high optical transparency and compatibility with OLED fabrication processes.
Implementation Method 1
which undergoes polymerization at elevated temperatures or radiation
Implementation Method 2
By matching the refractive index of the substrate (n=1.8) and organic layers and augmenting the distance of the emission zone to the cathode to suppress plasmonic losses light extraction into the substrate can be increased to 80-90%
Data Source
AI summary
Embodiments in accordance with the present invention encompass compositions encompassing a procatalyst and a thermal or photoactivator along with one or more monomers which undergo vinyl addition polymerization when said composition is heated to a temperature from 50 °C to 100 °C to form a substantially transparent film. The monomers employed therein have a range of refractive index from 1.4 to 1.6 and thus these compositions can be tailored to form transparent films of varied refractive indices. Accordingly, compositions of this invention are useful in various opto-electronic applications, including as coatings, encapsulants, fillers, leveling agents, among others.