Tungsten Oxide Hole Injection Layer for Organic EL

Solution Overview

Problem

The presence of adsorbates on the surface of the hole injection layer in organic EL elements, primarily carbon-containing species from the atmosphere or manufacturing impurities, leads to increased drive voltage and reduced longevity of the organic EL elements during the lamination process.

Innovation Solution

A tungsten oxide-based hole injection layer with a recessed structure and a bank configuration that covers the upper peripheral edge, ensuring a clean surface and maintaining the energy level from oxygen vacancies, thereby reducing adsorbate concentration and enhancing hole injection efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a hole injection layer is used to improve hole injection efficiency, then carrier injection is facilitated, but adsorbates on the surface increase drive voltage and reduce longevity

Engineering Contradiction:

Improvehole injection efficiencyVSAvoiddrive voltage increase due to adsorbates

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary cleaning action by irradiating the hole injection layer surface with ultraviolet light and/or oxygen plasma before subsequent layer formation. This preliminary treatment removes adsorbates that would otherwise increase drive voltage and reduce device longevity, while preserving the energy level structure necessary for efficient hole injection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the surface state parameters of the hole injection layer by controlling adsorbate concentration through ultraviolet irradiation and plasma treatment. This modifies the surface chemistry without fundamentally changing the bulk material properties, thereby reducing drive voltage while maintaining injection efficiency.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a hole injection layer is used to improve hole injection efficiency, then carrier injection is facilitated, but adsorbates reduce the longevity of the organic EL element

Engineering Contradiction:

Improvehole injection efficiencyVSAvoidlongevity of organic EL element

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent applies preliminary cleaning action by irradiating the hole injection layer surface with ultraviolet light and/or oxygen plasma before subsequent layer formation. This preliminary treatment removes adsorbates that would otherwise increase drive voltage and reduce device longevity, while preserving the energy level structure necessary for efficient hole injection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the surface state parameters of the hole injection layer by controlling adsorbate concentration through ultraviolet irradiation and plasma treatment. This modifies the surface chemistry without fundamentally changing the bulk material properties, thereby reducing drive voltage while maintaining injection efficiency.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If adsorbates are present on the hole injection layer surface, then the surface is ready for lamination, but the adsorbates are embedded between layers causing performance degradation

Engineering Contradiction:

Improvelamination processVSAvoidinterface quality between layers

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent applies preliminary cleaning action by irradiating the hole injection layer surface with ultraviolet light and/or oxygen plasma before subsequent layer formation. This preliminary treatment removes adsorbates that would otherwise be embedded during lamination, ensuring high interface quality while maintaining manufacturing feasibility.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the surface state parameters of the hole injection layer by controlling adsorbate concentration through ultraviolet irradiation and plasma treatment. This modifies the surface chemistry without fundamentally changing the bulk material properties, thereby reducing drive voltage while maintaining injection efficiency.

Inventive Principle:

Principle #35Parameter changes

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 allows for organic EL elements to operate at low voltage with high intensity emission, preventing uneven luminance and extending the service life by minimizing the impact of adsorbates and film loss.

Implementation Method 1

Upon application of voltage across the pair of electrodes, holes injected from the anode to the functional layer recombine with electrons injected from the cathode to the functional layer. The recombination causes the phenomenon of electroluminescence, which involves emission of light.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

An injection layer disposed between a functional layer and the anode is a hole injection layer composed of an organic material, such as copper phthalocyanine or PEDOT (conductive polymer), or of a metal oxide, such as molybdenum oxide or tungsten oxide.

Methodology Applied

Scientific EffectEnergy level modulation:

Implementation Method 3

it has become an important issue to reduce the concentration of such adsorbates by irradiation with ultraviolet light or oxygen plasma or by subjecting the surface to oxygen atmosphere after the formation of the hole injection layer

Methodology Applied

Scientific EffectPhotodesorption:

Implementation Method 4

it has become an important issue to reduce the concentration of such adsorbates by irradiation with ultraviolet light or oxygen plasma or by subjecting the surface to oxygen atmosphere after the formation of the hole injection layer

Methodology Applied

Scientific EffectPlasma: Plasma

Implementation Method 5

it has become an important issue to reduce the concentration of such adsorbates by irradiation with ultraviolet light or oxygen plasma or by subjecting the surface to oxygen atmosphere after the formation of the hole injection layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS9130187B2Organic EL element, display device, and light-emitting device

Publication Date: 2015.09.08 MAGNOLIA BLUE CORP

AI summary

The present invention aims to provide organic EL elements operating at low voltage to emit light at high intensity. For this aim, each EL element includes an anode, a cathode, a functional layer disposed between the anode and the cathode and including a light-emitting layer composed of organic material, a hole injection layer disposed between the anode and the functional layer, and a bank defining the light-emitting layer. The hole injection layer contains tungsten oxide and exhibits: by UPS measurement, a UPS spectrum having a protrusion appearing near a Fermi surface and within a region corresponding to a binding energy range lower than the top of a valence band; and by XPS measurement, that the tungsten oxide in the hole injection layer satisfies a condition that a ratio in number density of atoms other than tungsten atoms and oxygen atoms to the tungsten atoms is equal to 0.83 or smaller.