OLED Emissive Layer Suppression Mechanism for Color Saturation

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Solution Overview

Problem

Existing OLEDs face challenges in achieving saturated color emission, particularly in red, green, and blue pixels, with current technologies limited in efficiency and color range when using multiple dopants in the emissive layer.

Innovation Solution

The use of a device structure comprising an anode, cathode, and an organic emissive layer with a host and two or three phosphorescent compounds, where the first compound emits at a longer wavelength than the second or third compound, and a suppression mechanism, such as a micro-cavity, down-conversion filter, or optical filter, is employed to preferentially reduce the emission of the second or third compound, achieving specific CIE coordinates for desired color outputs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple phosphorescent dopants are used in the emissive layer to achieve wide color range, then color emission range is improved, but color saturation deteriorates due to overlapping emission spectra

Engineering Contradiction:

Improvecolor emission rangeVSAvoidcolor saturation

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent extracts and eliminates the harmful emission component by using a suppression mechanism (optical filter, microcavity, or wavelength converter) to selectively remove or convert the emission from the second phosphorescent dopant at its peak wavelength, while preserving the emission from the first dopant that contributes to the desired color

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the emission spectrum parameters by introducing a suppression mechanism that selectively targets specific wavelength ranges. This modifies the overall emission profile to achieve both wide color range and high saturation by suppressing unwanted spectral components

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If multiple dopants are used to achieve desired CIE coordinates, then color accuracy is improved, but device complexity increases due to additional suppression mechanisms

Engineering Contradiction:

ImproveCIE coordinate accuracyVSAvoidemissive layer structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The suppression mechanism serves multiple functions simultaneously: it suppresses emission from the second dopant at its peak wavelength, enhances color saturation, and helps achieve the desired CIE coordinates. This multi-functionality reduces the need for additional separate components

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent introduces an intermediary suppression mechanism that mediates between the multiple dopants. This intermediary component manages the interaction between dopants by selectively suppressing unwanted emission, simplifying the overall system design

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If the first phosphorescent compound is used at low concentration to achieve saturation, then color purity is improved, but emission intensity deteriorates

Engineering Contradiction:

Improvecolor purityVSAvoidemission intensity

Core Design Contradiction:

Manufacturing precisionVSIllumination intensity

Solution Approach 1:

The patent converts the potentially harmful effect of the second dopant's emission into a benefit by using it to provide overall emission intensity, while the suppression mechanism selectively removes its unwanted spectral components. The second dopant's emission is thus transformed from a source of color contamination to a source of luminous output

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

This approach enhances OLED performance by achieving a wide range of color emissions with improved efficiency, EQE, and superior lifetime, particularly for red phosphorescent OLEDs, by effectively managing the emission spectra of multiple dopants.

Implementation Method 1

The first compound is capable of phosphorescent emission at room temperature and is present in an amount less than 3 weight %. The second compound is capable of phosphorescent emission at room temperature

Methodology Applied

Scientific EffectPhosphorescence: Phosphorescence

Implementation Method 2

OLEDs make use of thin organic films that emit light when voltage is applied across the device

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 3

a suppression mechanism, such as a micro-cavity, down-conversion filter, or optical filter, is employed to preferentially reduce the emission of the second or third compound

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentUS9450198B2Organic electroluminescent materials and devices

Publication Date: 2016.09.20 UNIVERSAL DISPLAY CORP

AI summary

An OLED includes a suppression mechanism and multiple dopants in its organic emissive layer. The organic emissive layer includes a host, a first compound capable of phosphorescent emission at room temperature, and a second compound capable of phosphorescent emission at room temperature. The suppression mechanism is capable of preferentially reducing the emission of light emitted by the second compound. The organic emissive layer may also contain a third compound capable of phosphorescent emission at room temperature.