Quantum Dot Light Emitting Device Gradient Sub-Function Layers
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Solution Overview
Problem
Quantum dot light emitting diodes (QLEDs) face challenges with high turn-on voltage and low efficiency due to a high energy level barrier between the hole transport layer and the electron transport layer, limiting their further application in display technology.
Innovation Solution
A quantum dot light emitting device is designed with multiple sub-function layers in the light emitting functional layers, where the surface energies of ligands change in gradient, allowing for a matched energy level configuration that enhances carrier transmission and balance, comprising fluorine-containing, hydrophobic, and hydrophilic amine ligands, and inorganic nanoparticles with varying refractive indexes to form a stepped barrier and improve light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional single-layer electron transport layer and hole transport layer are used in QLED, then device structure is simple, but turn-on voltage is high and efficiency is low due to high energy level barrier
Solution Approach 1:
The electron transport layer and hole transport layer are divided into multiple sub-function layers with different energy levels. The electron transport layer includes a first sub-function layer, second sub-function layer, and third sub-function layer, each with progressively deeper LUMO energy levels. Similarly, the hole transport layer is segmented into sub-layers with progressively shallower HOMO energy levels. This segmentation creates stepped energy barriers that facilitate gradual carrier transport while maintaining overall structural organization.
Solution Approach 2:
Each sub-function layer is assigned specific local properties including distinct energy levels, surface energies, and refractive indexes. The first sub-function layer of the electron transport layer has higher surface energy and shallower LUMO level, while the third sub-function layer has lower surface energy and deeper LUMO level. This local differentiation of properties enables optimized carrier injection at each interface while managing overall device performance.
2Loss of energy
If multiple sub-function layers with gradient surface energies are introduced to reduce energy barrier, then carrier transmission is improved, but device complexity increases
Solution Approach 1:
The patent systematically changes key parameters across the sub-function layers including surface energy, LUMO energy level, HOMO energy level, and refractive index. Surface energy decreases from the first to third sub-function layer in the electron transport layer, while LUMO energy levels deepen progressively. These parameter gradients create favorable energy alignment at each interface, enabling efficient carrier transport through the multiple layers without requiring excessive complexity.
Solution Approach 2:
The intermediate sub-function layers act as mediators between the quantum dot light emitting layer and the electrode. The second sub-function layer of the electron transport layer and the second sub-function layer of the hole transport layer serve as intermediate structures that bridge the energy gap between the quantum dot layer and respective electrodes, facilitating smooth carrier transition through energy level alignment.
3Loss of energy
If gradient refractive index layers are used to improve light extraction, then light emission efficiency increases, but manufacturing complexity increases
Solution Approach 1:
The patent combines multiple functions into the sub-function layers: each layer simultaneously provides carrier transport, energy level alignment, and light extraction functions. The gradient refractive index structure is integrated with the gradient energy level structure, so that the same sub-function layers that facilitate carrier transport also enable progressive light extraction. This merging reduces the need for separate dedicated light extraction layers, simplifying the overall manufacturing process while achieving multiple benefits.
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 reduces the turn-on voltage and increases efficiency by aligning energy levels and refractive indexes, improving carrier injection and light emission, thus enhancing the performance of QLEDs for display applications.
Implementation Method 1
surface energies of the ligands corresponding to sub-function layers change in gradient along a transmission direction of carriers in the sub-function layers, so that energy levels of the sub-function layers change in gradient
Implementation Method 2
inorganic nanoparticles with varying refractive indexes to form a stepped barrier and improve light extraction efficiency
Implementation Method 3
quantum dot light emitting device
Data Source
AI summary
The present disclosure discloses a quantum dot light emitting device, a preparation method therefor and a display apparatus. In the present disclosure, at least one of one or more layers of light emitting functional layers is disposed to include at least two sub-function layers, the sub-function layers comprise ligands, and surface energies of the ligands corresponding to sub-function layers change in gradient along a transmission direction of carriers in the sub-function layers, so that energy levels of the sub-function layers change in gradient. In this way, the energy levels of the sub-function layers can be matched with the energy levels of the adjacent light emitting function layers, so that carrier transmission and balance as well as device efficiency can be improved.