Quantum-dot Light Emitting Diode Charge Balance

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Solution Overview

Problem

The charge balance in quantum-dot (QD) light emitting diodes is degraded due to slower hole injection rates compared to electron injection rates, leading to decreased emitting efficiency.

Innovation Solution

Incorporating first and second charge auxiliary layers between the QD emitting material layers and electrodes, where the first charge auxiliary layer contacts the ligand and the second charge auxiliary layer contacts the shell of the QD, and using a dry-etching process to remove the ligand from one side of the QD surface, enhancing electron and hole injection rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional QD emitting layer structure is used, then device structure is simple, but charge balance is degraded and emitting efficiency is decreased

Engineering Contradiction:

Improvestructure simplicityVSAvoidemitting efficiency

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The charge auxiliary layer is segmented into two distinct functional layers: a first charge auxiliary layer contacting the ligand for hole injection, and a second charge auxiliary layer contacting the shell for electron injection. This segmentation allows independent optimization of electron and hole injection rates, resolving the charge balance degradation issue while maintaining manufacturing simplicity through sequential layer deposition.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the QD structure are treated with different properties: the ligand surface is modified with a first charge auxiliary layer having hole transport characteristics, while the shell surface is modified with a second charge auxiliary layer having electron transport characteristics. This local quality differentiation enables optimized charge injection at each interface, improving overall emitting efficiency without complicating the global device structure.

Inventive Principle:

Principle #3Local quality

2Reliability

If hole injection rate is increased to improve charge balance, then charge balance improves, but electron injection rate becomes excessively high causing new imbalance

Engineering Contradiction:

Improvecharge balanceVSAvoidinjection rate balance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

Two intermediary charge auxiliary layers are introduced between the electrodes and the QD emitting layer. The first charge auxiliary layer acts as an intermediary for hole injection by contacting the ligand, while the second charge auxiliary layer acts as an intermediary for electron injection by contacting the shell. These intermediaries mediate the charge transfer process, enabling balanced electron and hole injection rates without direct electrode-QD interaction.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If ligand is removed from entire QD surface to improve electron injection, then electron injection rate increases, but hole injection rate decreases and charge balance deteriorates

Engineering Contradiction:

Improveelectron injection rateVSAvoidcharge balance

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

Instead of uniformly removing the ligand from the entire QD surface, the invention applies local quality modification: the ligand is selectively removed or modified only in the region contacting the first charge auxiliary layer to facilitate hole injection, while the shell region contacting the second charge auxiliary layer is prepared for electron injection. This localized approach enables independent optimization of electron and hole injection without compromising charge 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 improves charge balance and emitting efficiency by increasing electron and hole injection rates, thereby enhancing the performance of QD light emitting diodes and display devices.

Implementation Method 1

In the QD, an electron in unstable state transitions from a conduction band to a valence band such that light is emitted

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Implementation Method 2

using a dry-etching process to remove the ligand from one side of the QD surface

Methodology Applied

Scientific EffectDry-etching:

Data Source

PatentUS10873048B2Quantum-dot light emitting diode, method of fabricating the quantum-dot light emitting diode and quantum-dot light emitting display device

Publication Date: 2020.12.22 LG DISPLAY CO LTD

AI summary

A quantum-dot (QD) light emitting diode and a quantum-dot light emitting display device are disclosed. The QD light emitting diode includes first and second electrodes facing each other; a QD emitting material layer between the first and second electrodes and including a QD; a first charge auxiliary layer between the first electrode and the QD emitting material layer; and a second charge auxiliary layer between the QD emitting material layer and the second electrode, wherein the QD includes a core, a shell surrounding the core and a ligand contacting a portion of the shell, and wherein the first charge auxiliary layer contacts the ligand, and the second charge auxiliary layer contacts the shell.