Quantum Dot Electroluminescent Device with Asymmetric Ligand Distribution
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Solution Overview
Problem
Conventional quantum dot electroluminescent devices face challenges with high turn-on and operating voltages, carrier injection efficiency due to large band offsets between quantum dots and hole transport layer materials, and difficulties in finding suitable HTL materials with high enough HOMO levels.
Innovation Solution
A quantum dot electroluminescent device with a QD light-emitting layer having different organic ligand distributions on its surfaces, where the first surface in contact with the HTL and the second surface in contact with the ETL, facilitating reduced band offsets and improved carrier injection efficiency by using a polymer-based HTL and surface modification to control the band levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional HTL material with HOMO level between 5.0-5.3 eV is used, then the device structure is simple and easy to manufacture, but the large band offset between HTL and quantum dots causes high turn-on voltage and poor carrier injection efficiency
Solution Approach 1:
The patent changes the HOMO level parameter of the HTL material to 5.4 eV or higher, which reduces the band offset with quantum dots (valence band ~6.8 eV) and improves carrier injection efficiency while maintaining device manufacturability
Solution Approach 2:
The patent uses a composite structure combining HTL material with quantum dots, where the HTL layer with optimized HOMO level (5.4 eV or higher) works synergistically with the quantum dot light-emitting layer to achieve both good color purity and high carrier injection efficiency
2Reliability
If a HTL material with HOMO level of 5.4 eV or above is used, then the band offset between HTL and quantum dots is reduced improving carrier injection, but a large band offset is created between HTL and ITO anode making hole migration difficult
Solution Approach 1:
The patent optimizes the HOMO level parameter to a specific range (5.4 eV or higher) that balances two competing requirements: reducing band offset with quantum dots for efficient carrier injection while maintaining sufficient hole migration capability from the ITO anode
Solution Approach 2:
The patent applies different material properties at different locations: the HTL material with HOMO level of 5.4 eV or higher is positioned between the ITO anode and quantum dots, creating localized optimal conditions for both hole injection from anode and carrier injection into quantum dots
3Ease of manufacture
If the quantum dot light-emitting layer has uniform organic ligand distribution, then the manufacturing process is simple, but the turn-on voltage and operating voltage remain high
Solution Approach 1:
The patent creates different organic ligand distributions at different surfaces of the quantum dot light-emitting layer: the first surface in contact with HTL has one ligand distribution optimized for carrier injection, while the second surface in contact with ETL has another ligand distribution optimized for electron transport, thereby reducing both turn-on and operating voltages
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
The solution results in a device with lower turn-on voltage, lower operating voltage, and higher luminescence efficiency, enhancing the overall performance of the quantum dot electroluminescent device.
Implementation Method 1
The small size of a quantum dot results in a large surface area per unit volume. This allows most of the constituent atoms to be exposed to the surface, and gives rise to various effects, including quantum confinement. By taking advantage of the quantum confinement effect, the emission wavelength of the quantum dots may be controlled by varying the size of the quantum dots.
Implementation Method 2
quantum dots have received a great deal of attention in the display arts for their advantages such as good color purity and high photoluminescence ('PL') efficiency
Data Source
Figure 1
Figure 2a~2b
Figure 3(A)~3(D)
AI summary
A quantum dot electroluminescent device that includes a substrate, a quantum dot light-emitting layer disposed on the substrate, a first electrode which injects charge carriers into the quantum dot light-emitting layer, a second electrode which injects charge carriers, which have an opposite charge than the charge carriers injected by the first electrode, into the quantum dot light-emitting layer, a hole transport layer disposed between the first electrode and the quantum dot light-emitting layer, and an electron transport layer disposed between the second electrode and the quantum dot light-emitting layer, wherein the quantum dot light-emitting layer has a first surface in contact with the hole transport layer and a second surface in contact with an electron transport layer, and wherein the first surface has an organic ligand distribution that is different from an organic ligand distribution of the second surface.