OLED Redox-Doped Electron Transport Layer Stack

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Solution Overview

Problem

Existing organic light-emitting diodes (OLEDs) face challenges in achieving low operational voltages while maintaining high brightness and balanced hole and electron injection, which affects efficiency and lifetime.

Innovation Solution

The use of a specific electron transport layer stack comprising a first electron transport layer with a matrix compound and a second electron transport layer doped with a redox n-dopant, arranged between the emission layer and the cathode, to enhance charge transport and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single electron transport layer is used, then the device structure is simple, but the operational voltage is high and efficiency is low

Engineering Contradiction:

Improveelectron transport layer structureVSAvoidoperational voltage

Core Design Contradiction:

Device complexityVSUse of energy by moving object

Solution Approach 1:

The electron transport layer is divided into two distinct layers: a first electron transport layer adjacent to the emission layer and a second electron transport layer adjacent to the cathode. This segmentation allows each layer to be optimized for specific functions, resulting in reduced operational voltage and improved efficiency without excessive complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each electron transport layer is assigned different material compositions and properties tailored to its specific location and function. The first layer uses materials optimized for electron transport from the emission layer, while the second layer uses materials optimized for electron injection from the cathode, creating local quality optimization that reduces overall operational voltage.

Inventive Principle:

Principle #3Local quality

2Productivity

If redox doping is applied to increase charge carrier concentration, then efficiency improves, but device complexity increases

Engineering Contradiction:

Improvecharge carrier concentrationVSAvoiddoping process

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

Redox dopants are incorporated into the electron transport layers during the material deposition process rather than requiring post-fabrication doping steps. This preliminary action allows charge carrier concentration to be optimized while maintaining relatively simple device fabrication processes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The redox doping modifies the electrical parameters of the electron transport layers by introducing charge carriers, which changes the conductivity and charge transport properties. This parameter change achieves high charge carrier concentration through material composition optimization rather than complex structural modifications.

Inventive Principle:

Principle #35Parameter changes

3Illumination intensity

If electron transport is enhanced, then brightness increases, but hole-electron balance deteriorates

Engineering Contradiction:

ImprovebrightnessVSAvoidhole-electron balance

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The segmented electron transport layer structure allows independent optimization of electron transport in each layer while maintaining overall charge balance. The first layer focuses on electron transport from the emission layer, while the second layer manages electron injection and overall charge balance, preventing excessive electron accumulation that would disrupt hole-electron balance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different materials with tailored electron mobility and energy level characteristics are used in each electron transport layer to locally optimize electron transport while maintaining global charge balance. This local quality approach ensures high brightness without compromising hole-electron balance.

Inventive Principle:

Principle #3Local quality

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 configuration results in improved external quantum efficiency, reduced operating voltage, and extended lifetime of OLEDs, particularly in top and bottom emission devices.

Implementation Method 1

redox doping which generates doped layers with high charge carrier concentrations

Methodology Applied

Scientific EffectRedox reactions: Redox Reactions

Implementation Method 2

electrons injected from the cathode move to the EML, via the ETL

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS11532801B2Organic electroluminescent device comprising a redox-doped electron transport layer and an auxiliary electron transport layer

Publication Date: 2022.12.20 NOVALED GMBH

AI summary

The present invention relates to an organic electroluminescent device, particularly to an organic light emitting diode (OLED) including an ETL stack of at least two electron transport layers, wherein the first electron transport layer comprises a first electron transport matrix compound and the second electron transport layer comprises second electron transport matrix compound and a redox n-dopant, and a device comprising the OLED.