OLED Electron-Injecting Layer Reduces Drive Voltage

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Solution Overview

Problem

Organic electroluminescent devices (OLEDs) face challenges in achieving low drive voltage, high efficiency, and long lifetime, particularly in tandem OLEDs, where increased drive voltage and metallic dopant-induced excited-state quenching lower luminance efficiency and shorten device lifetime.

Innovation Solution

Incorporating an electron-injecting layer with a metal dopant having a work function less than 4.0 eV and an electron-transporting material different from the first electron-transporting material, adjacent to the cathode, to reduce voltage while maintaining efficiency and extending the OLED's operational life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If an electron-injecting layer with metallic dopant is provided between the cathode and the light-emitting layer to reduce drive voltage, then drive voltage is reduced, but excited-state quenching occurs and luminance efficiency decreases

Engineering Contradiction:

Improvedrive voltageVSAvoidluminance efficiency

Core Design Contradiction:

PowerVSLoss of energy

Solution Approach 1:

An electron-transporting layer is introduced as an intermediary between the electron-injecting layer (containing metallic dopant) and the light-emitting layer. This intermediary layer prevents direct contact between the metallic dopant and the light-emitting layer, thereby eliminating excited-state quenching while still allowing the electron-injecting layer to perform its voltage-reducing function. The electron-transporting layer acts as a protective barrier that maintains luminance efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The device is divided into functionally distinct layers: an electron-injecting layer for voltage reduction, an electron-transporting layer for protection and transport, and a light-emitting layer for light generation. This segmentation allows each layer to optimize its specific function without interfering with others, particularly preventing the metallic dopant from quenching the light-emitting layer while maintaining low drive voltage.

Inventive Principle:

Principle #1Segmentation

2Power

If an electron-injecting layer with metallic dopant is provided to reduce drive voltage, then drive voltage is reduced, but device lifetime is shortened

Engineering Contradiction:

Improvedrive voltageVSAvoiddevice lifetime

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The electron-transporting layer serves as a protective intermediary that prevents metallic dopant diffusion into the light-emitting layer. By blocking the diffusion path, this intermediary layer eliminates the degradation mechanism that would otherwise shorten device lifetime, while allowing the electron-injecting layer to maintain low drive voltage operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Illumination intensity

If high current density is used to achieve high brightness, then luminance is increased, but lifetime is reduced

Engineering Contradiction:

ImproveluminanceVSAvoidlifetime

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The invention changes the electrical parameters of the device by introducing the electron-injecting layer, which enables operation at lower current densities. The low-work-function metallic dopant in the electron-injecting layer facilitates easier electron injection, reducing the voltage and current required to achieve target luminance levels, thereby extending device lifetime while maintaining high brightness.

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

This configuration reduces drive voltage, enhances luminous efficiency, and prolongs the OLED's operational life by minimizing excited-state quenching and metal dopant diffusion, while maintaining desirable chromaticity for broadband or white light emission.

Implementation Method 1

an electron-injecting layer disposed between the electron-transporting layer and the cathode, such electron-injecting layer including a metal dopant having a work function less than 4.0 eV

Methodology Applied

Scientific EffectElectron injection:

Implementation Method 2

an electron-transporting layer disposed between the at least one light-emitting layer and the cathode, such electron-transporting layer including a first electron-transporting material

Methodology Applied

Scientific EffectElectron transport:

Implementation Method 3

Holes and electrons recombine and emit light in the ETL near the interface of HTL/ETL

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS8057916B2OLED device with improved performance

Publication Date: 2011.11.15 GLOBAL OLED TECHNOLOGY LLC

AI summary

An OLED device includes an anode, a cathode, and at least one individually selected organic light-emitting layer disposed between the anode and cathode. The device also includes an electron-transporting layer disposed between the at least one light-emitting layer and the cathode, such electron-transporting layer including a first electron-transporting material, and an electron-injecting layer disposed between the electron-transporting layer and the cathode, such electron-injecting layer including a metal dopant having a work function less than 4.0 eV and an electron-transporting material that is different from the first electron-transporting material.