Light-Emitting Device Host Mobility Gradient for Lifespan

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Solution Overview

Problem

In light-emitting devices, the strong electron transporting characteristics of single-host emission layers lead to triplet-triplet fusion at the electron blocking layer interface, causing deterioration and reducing the lifespan of the device.

Innovation Solution

A light-emitting device with a structure including a first emission layer and a second emission layer, where the hole mobilities and triplet energy levels of the hosts satisfy specific conditions, allowing hole-electron recombination to occur at the interface between the layers, thereby preventing electron blocking layer deterioration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a single-host emission layer with strong electron transporting characteristics is used, then electron transport efficiency is improved, but triplet-triplet fusion occurs at the electron blocking layer interface causing device deterioration and reduced lifespan

Engineering Contradiction:

Improveelectron transport efficiencyVSAvoiddevice lifespan

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The emission layer is divided into multiple emission layers with different host materials (first host, second host, third host) having different hole mobilities. This segmentation allows different regions to perform different functions: the first emission layer with high hole mobility prevents triplet-triplet fusion at the interface, while other layers maintain electron transport efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different host materials are used in different emission layers to create local variations in hole mobility. The first emission layer uses a host with higher hole mobility specifically at the interface region to prevent triplet-triplet fusion, while other layers use hosts optimized for their specific functions, achieving local optimization of device performance.

Inventive Principle:

Principle #3Local quality

2Reliability

If the recombination zone is located at the electron blocking layer interface, then electron blocking layer deterioration occurs, but if moved to the interface between emission layers, then device lifespan is improved

Engineering Contradiction:

Improvedevice lifespanVSAvoidelectron blocking layer deterioration

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The recombination zone is extracted from the electron blocking layer interface and relocated to the interface between the first and second emission layers. This is achieved by designing the hole mobility gradient such that holes accumulate at the emission layer interface rather than at the electron blocking layer, thereby removing the harmful effect from the electron blocking layer.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The first emission layer acts as an intermediary between the electron blocking layer and the second emission layer. By positioning the recombination zone at the interface between emission layers rather than directly at the electron blocking layer interface, the first emission layer mediates and protects the electron blocking layer from deterioration caused by triplet-triplet fusion.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If hole mobility of hosts is optimized to prevent triplet-triplet fusion, then device lifespan is improved, but device complexity increases due to multiple hosts with specific mobility requirements

Engineering Contradiction:

Improvedevice lifespanVSAvoidemission layer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention changes the key parameter of hole mobility across different emission layers to prevent triplet-triplet fusion. By systematically varying the hole mobility parameter (μH1 > μH2 and μH1 > μH3) rather than changing the overall device architecture, the solution achieves improved reliability with controlled complexity through parameter optimization rather than structural complexity.

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 enhances the lifespan and efficiency of light-emitting devices by moving the recombination zone to the interface between the emission layers, improving luminance and reducing driving voltage.

Implementation Method 1

Carriers, such as holes and electrons, recombine in such an emission layer region to produce excitons. These excitons transition from an excited state to a ground state to thereby generate light.

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS20230165022A1Light-emitting device and electronic apparatus including the same

Publication Date: 2023.05.25 SAMSUNG DISPLAY CO LTD

AI summary

In a light-emitting device, an emission layer includes a first emission layer and a second emission layer, the first emission layer includes a first host, the second emission layer includes a second host and a third host, and a hole mobility of the first host (μH1), a hole mobility of the second host (μH2), and a hole mobility of the third host (μH3) satisfy Expressions (1) and (2) below:μH1>μH2 (1)μH1>μH3 (2).