Quantum Dot LED Electron Transporting Layer Charge Balance

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Solution Overview

Problem

Quantum-dot (QD) light emitting diodes face challenges with charge balance and emitting efficiency due to the deep highest occupied molecular orbital (HOMO) level of QDs, leading to decreased performance and lifespan.

Innovation Solution

Incorporating an electron transporting layer with both electron-property and hole-property materials, where the electron-property material has a higher electron mobility than hole mobility, and the hole-property material has a higher hole mobility, to improve charge balance and emitting efficiency by forming an exciplex that enhances light emission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a conventional QD emitting layer is used, then the device structure is simple, but the charge balance is poor and emitting efficiency is decreased due to the deep HOMO level of QDs

Engineering Contradiction:

Improvedevice structureVSAvoidcharge balance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The emitting layer is segmented into multiple sub-layers: a first emitting sub-layer containing QDs and a hole transporting material, and a second emitting sub-layer containing an electron transporting material and a hole transporting material. This segmentation allows each sub-layer to specialize in different charge carrier functions, improving overall charge balance while maintaining a relatively simple overall device structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the emitting layer are assigned different material compositions and functions. The first emitting sub-layer focuses on hole transport and QD emission, while the second emitting sub-layer focuses on electron transport and additional hole transport. This local differentiation of material properties optimizes charge balance without requiring complete structural redesign.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If a conventional QD emitting layer is used, then the device is easy to manufacture, but the emitting efficiency is decreased due to the deep HOMO level

Engineering Contradiction:

Improveease of manufactureVSAvoidemitting efficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The emitting layer uses composite materials combining QDs with specific hole transporting materials in the first sub-layer, and electron transporting materials with hole transporting materials in the second sub-layer. These composite material systems are designed to have complementary energy levels that overcome the deep HOMO level limitation while maintaining compatibility with conventional manufacturing processes.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The energy level parameters of the materials are carefully selected and adjusted. The hole transporting material in the first sub-layer and the electron transporting material in the second sub-layer are chosen to have appropriate HOMO and LUMO levels that create favorable energy gradients for charge injection and transport, thereby improving emitting efficiency without complicating manufacturing.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If the QD has a deep HOMO level, then the QD maintains its inherent properties, but the charge balance in the emitting layer is poor

Engineering Contradiction:

ImproveQD propertiesVSAvoidcharge balance

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

Hole transporting materials are introduced as intermediaries between the QDs and the electrodes. These intermediary materials have appropriate energy levels that bridge the gap created by the deep HOMO level of QDs, facilitating balanced charge transport while leaving the QD composition and intrinsic properties unchanged.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The emitting layer structure is designed to self-compensate for the deep HOMO level effect. The dual sub-layer configuration with different material functions creates internal charge balance mechanisms that automatically adjust charge distribution, allowing the QDs to maintain their inherent properties while the overall system achieves improved charge balance.

Inventive Principle:

Principle #25Self-service

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 increases the emitting efficiency and lifespan of QD light emitting diodes by adjusting the electron and hole injection rates, resulting in enhanced light emission properties.

Implementation Method 1

Methodology Applied

Scientific EffectExciplex formation:

Implementation Method 2

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 EffectElectron transition and light emission: Electroluminescence

Data Source

PatentUS11489130B2Quantum-dot light emitting diode and quantum-dot light emitting display device including the same

Publication Date: 2022.11.01 LG DISPLAY CO LTD

AI summary

The present disclosure provides a quantum dot (QD) light emitting diode including: a first electrode and a second electrode facing each other; a QD emitting material layer positioned between the first electrode and the second electrode and including a QD; a hole auxiliary layer positioned between the first electrode and the QD emitting material layer; and an electron transporting layer positioned between the QD emitting material layer and the second electrode and including an electron-property material and a hole-property material.