Quantum Dot Light Emitting Device Dual Ligand Hole Injection
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Solution Overview
Problem
Quantum dot light emitting devices face an electron-hole imbalance issue due to difficulties in injecting holes with large energy level differences into the light emitting layer, affecting performance and lifetime.
Innovation Solution
Incorporating a quantum dot light emitting layer with a first ligand having a chain structure adjacent to the electron transport layer and a second ligand with a ring structure, such as pyridine, shorter in length, to facilitate balanced electron and hole injection, along with a multilayer structure and specific materials like cadmium selenide and zinc oxide, to improve hole transport and injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If holes are injected into the light emitting layer, then the light emitting function is achieved, but the large energy level difference prevents ready injection, causing electron-hole imbalance
Solution Approach 1:
The patent introduces a hole transport layer as an intermediary between the anode and the quantum dot light emitting layer. This intermediate layer has energy levels that bridge the gap between the anode and the quantum dots, facilitating hole injection. Additionally, surface ligands on the quantum dots act as intermediaries to modify the energy level alignment and improve hole transport into the light emitting layer.
Solution Approach 2:
The patent modifies the energy level parameters of the system by selecting specific materials for the hole transport layer and by controlling the surface ligands of quantum dots. These parameter changes adjust the energy level differences to enable efficient hole injection while maintaining electron transport, thereby achieving electron-hole balance.
2Reliability
If a single type of ligand is used on quantum dot surface, then the structure is simple, but the electron-hole injection balance is poor
Solution Approach 1:
The patent applies different types of ligands at different locations on the quantum dot surface. Specifically, hydrophobic ligands are used in regions favorable for electron injection, while hydrophilic ligands are used in regions favorable for hole injection. This local differentiation of ligand properties optimizes the injection characteristics for each charge carrier type without requiring a completely complex overall structure.
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 hole injection efficiency, reducing electron-hole imbalance, leading to improved brightness, current efficiency, and power efficiency, and supports high color reproduction capabilities.
Implementation Method 1
A quantum dot light emitting device refers to a device which emits light by itself upon combination of electrons and holes injected from both electrodes of a light emitting layer including quantum dots
Data Source
AI summary
Provided is a light emitting device including a lower electrode, an upper electrode disposed to face the lower electrode, a quantum dot light emitting layer between the lower electrode and the upper electrode, an electron transport layer between the lower electrode and the quantum dot light emitting layer, and a hole transport layer between the upper electrode and the quantum dot light emitting layer, wherein the quantum dot light emitting layer includes a quantum dot, and a first ligand on a surface of the quantum dot, and a second ligand on the surface of the quantum dot.