Top-Emitting OLED Cathode with Mg-Ag Alloy Buffer Layer

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Solution Overview

Problem

The high-energy sputtering process used to deposit metal oxides in top-emitting organic electroluminescent devices can damage the underlying organic layer, reducing efficiency and lifetime, and increasing film thickness to lower square resistance also shortens the device's lifespan.

Innovation Solution

A top-emitting organic electroluminescent device structure with a transparent metal layer and a transparent metal oxide layer, optionally including transparent metal strips, is used to reduce damage during sputtering, enhancing stability and transmittance while minimizing square resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If high-energy sputtering process is used to deposit metal oxide cathode layer, then light transmittance of cathode is increased, but organic functional layer is damaged leading to reduced efficiency and lifetime

Engineering Contradiction:

Improvelight transmittanceVSAvoiddevice lifetime

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

A low-work-function metal layer (magnesium-silver alloy) is introduced as an intermediary between the organic functional layer and the transparent metal oxide layer. This intermediate layer acts as a buffer that protects the organic layer from high-energy sputtering damage while still allowing the metal oxide layer to provide high light transmittance. The metal layer has work function of 3.7 eV which is lower than ITO, enabling efficient electron injection without damaging the underlying organic layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The cathode is designed as a composite structure combining transparent metal oxide (ITO or ZnO:In) with a magnesium-silver alloy metal layer. This composite cathode structure leverages the high transmittance properties of the metal oxide while the metal layer provides protection against sputtering damage and maintains low work function for efficient electron injection. The composite structure achieves both high transmittance and high reliability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If thickness of metal oxide film is increased to reduce square resistance, then cathode conductivity is improved, but device lifetime is reduced due to increased damage to organic layer

Engineering Contradiction:

Improvecathode conductivityVSAvoiddevice lifetime

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The magnesium-silver alloy metal layer serves as an intermediary that enables the metal oxide layer to be deposited with sufficient thickness for good conductivity without directly damaging the organic functional layer. The metal layer absorbs the sputtering energy that would otherwise damage the organic layer, allowing thicker metal oxide films to be deposited safely.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The work function parameter of the cathode is optimized by using magnesium-silver alloy with work function of 3.7 eV, which is lower than conventional ITO. This parameter change enables efficient electron injection at lower energies, reducing damage to the organic layer while maintaining good conductivity. The thickness of metal oxide is also optimized at 5-20 nm to balance conductivity and damage reduction.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional ITO cathode is used, then manufacturing process is simple, but light transmittance is insufficient and square resistance is large

Engineering Contradiction:

Improvemanufacturing process simplicityVSAvoidlight transmittance

Core Design Contradiction:

Ease of manufactureVSIllumination intensity

Solution Approach 1:

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The optical and electrical parameters of the cathode are optimized by changing from conventional thick ITO to a thin metal oxide layer (5-20 nm) combined with a low-work-function metal layer. This parameter change achieves higher light transmittance (improving by 10-15%) and lower square resistance while maintaining ease of manufacture through sputtering deposition.

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 achieves a cathode with high stability and high transmittance, improving the device's efficiency and extending its lifetime by reducing damage to the organic layer and lowering square resistance.

Implementation Method 1

a transparent metal oxide layer disposed on a surface of the transparent metal layer facing away from the organic functional layer

Methodology Applied

Scientific EffectSputtering: Sputtering

Implementation Method 2

organic electroluminescent device with a top-emitting structure has a strong selectivity for color of emitted light

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS10818869B2Top-emitting type organic electroluminescent device, manufacturing method thereof and display apparatus

Publication Date: 2020.10.27 BOE TECHNOLOGY GROUP CO LTD

AI summary

A top-emitting type organic electroluminescent device, a manufacturing method thereof and a display apparatus are disclosed. The top-emitting type organic electroluminescent device includes an anode, an organic functional layer and a cathode that are sequentially stacked. The cathode includes a transparent metal layer disposed on a surface of the organic functional layer facing away from the anode, and a transparent metal oxide layer disposed on a surface of the transparent metal layer facing away from the organic functional layer.