Silicon Nitride Barrier for OLED Thermal Stability

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Solution Overview

Problem

Organic electroluminescent display devices face issues with thermal durability due to fluctuations in in-plane retardation caused by exposure to high temperatures, especially when using polarizing plates with polymerizable liquid crystal compounds exhibiting reverse wavelength dispersibility.

Innovation Solution

Incorporating a silicon nitride layer between the circularly polarizing plate and the organic electroluminescent display element, with a polarizer of 10 μm or less thickness containing polyvinyl alcohol-based resin or dichroic organic coloring agents, and low moisture permeability substrates to reduce moisture and ammonia generation, thereby stabilizing the optically anisotropic layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a polarizing plate with polymerizable liquid crystal compound having reverse wavelength dispersibility is used, then the optically anisotropic layer can be thinned to meet thinning demands, but in-plane retardation fluctuates significantly when exposed to high temperature causing change in tint

Engineering Contradiction:

Improvethickness of optically anisotropic layerVSAvoidthermal durability

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

A silicon nitride layer is introduced as an intermediary barrier layer between the optically anisotropic layer and the organic light emitting element. This layer prevents ammonia generated from the organic light emitting element from reaching and decomposing the polymerizable liquid crystal compound, thereby maintaining in-plane retardation stability under high temperature conditions while keeping the optically anisotropic layer thin

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent uses a composite structure combining the silicon nitride layer with the polymerizable liquid crystal compound-based optically anisotropic layer. The silicon nitride layer provides thermal and chemical stability, protecting the polymerizable liquid crystal compound from degradation while maintaining the desired optical properties and thin profile

Inventive Principle:

Principle #40Composite materials

2Volume of moving object

If the optically anisotropic layer is thinned to meet thinning demands, then the apparatus thickness is reduced, but the layer becomes more vulnerable to decomposition under high temperature exposure

Engineering Contradiction:

Improvethickness of optically anisotropic layerVSAvoiddecomposition under high temperature

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The silicon nitride layer serves as a protective intermediary that blocks harmful ammonia and moisture from reaching the thinned optically anisotropic layer, preventing decomposition under high temperature conditions while allowing the layer to maintain its reduced thickness

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The silicon nitride layer creates an inert protective environment around the optically anisotropic layer, isolating it from reactive species (ammonia and moisture) that would otherwise cause decomposition under high temperature exposure

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

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 configuration enhances thermal durability by suppressing decomposition of the polymerizable liquid crystal compound and maintaining consistent in-plane retardation, improving the stability of the organic electroluminescent display device under high-temperature conditions.

Implementation Method 1

a silicon nitride layer is often installed to block oxygen and moisture

Methodology Applied

Scientific EffectMoisture barrier: Permeation

Implementation Method 2

the silicon nitride layer...reduce moisture and ammonia generation

Methodology Applied

Scientific EffectAmmonia generation suppression: Hydrolysis

Implementation Method 3

a polymerizable liquid crystal compound having reverse wavelength dispersibility...the optically anisotropic layer is a layer formed of a composition containing a polymerizable liquid crystal compound exhibiting reverse wavelength dispersibility

Methodology Applied

Scientific EffectReverse wavelength dispersibility: Birefringence

Implementation Method 4

the polarizer is a polarizer having a thickness of 10 μm or less and containing a polyvinyl alcohol-based resin, or a polarizer having a dichroic organic coloring agent

Methodology Applied

Scientific EffectPolarization: Polarisation

Data Source

PatentUS20220190303A1Organic electroluminescent display device

Publication Date: 2022.06.16 FUJIFILM CORP

AI summary

Provided is an organic electroluminescent display device having excellent thermal durability including, in order from a visual recognition side, at least a circularly polarizing plate, and an organic electroluminescent display element having a pair of electrodes and an organic light emitting layer sandwiched therebetween, in which the circularly polarizing plate has a polarizer and an optically anisotropic layer, the polarizer having a thickness of 10 μm or less and containing a polyvinyl alcohol-based resin, or having a dichroic organic coloring agent, the optically anisotropic layer being formed of a composition containing a polymerizable liquid crystal compound exhibiting reverse wavelength dispersibility, a silicon nitride layer being included between the circularly polarizing plate and the organic electroluminescent display element, and the circularly polarizing plate being disposed between two substrates having a moisture permeability of 1 g/m2·day or less, and one of the low moisture permeability substrates is the silicon nitride layer.