Crosslinked Quantum Dot Emissive Layer for Stable QLEDs
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Solution Overview
Problem
Existing light-emitting devices with quantum dots face challenges in achieving uniform and stable emission layers, particularly in multicolor displays, due to the instability of quantum dot layers during solvent rinsing and the complexity of fabrication methods.
Innovation Solution
A cross-linked emissive layer is developed, where quantum dots are dispersed in a cross-linked material, forming a combined charge transport and emissive layer (CCTEL), which is resistant to solvent rinsing and simplifies fabrication by integrating charge transport and emissive functions. This layer is formed using a solution containing quantum dots, cross-linkable material, and ligands, with specific ligand concentrations and distribution within the cross-linked network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If quantum dots are deposited using solution process methods, then fabrication cost and complexity are reduced, but the emissive layer becomes unstable during solvent rinsing
Solution Approach 1:
The patent combines quantum dots with cross-linkable organic materials to create a composite emissive layer. The quantum dots are dispersed within the cross-linkable matrix, forming a composite structure that maintains the advantages of solution processing while adding solvent resistance through cross-linking. This composite approach allows the emissive layer to retain quantum dot functionality while gaining structural stability.
Solution Approach 2:
The patent changes the chemical state of the emissive layer by introducing cross-linkable functional groups and applying cross-linking reactions. This parameter change transforms the emissive layer from a soluble state to a cross-linked insoluble state, providing solvent resistance while maintaining the solution processing advantage. The cross-linking degree and network structure are controlled to optimize both stability and emission performance.
2Device complexity
If separate charge transport layer and emissive layer are used, then device structure is well-defined, but fabrication process becomes more complex
Solution Approach 1:
The patent merges the charge transport layer and emissive layer into a single combined layer. The cross-linkable organic material serves dual functions: as a charge transport medium and as an emissive matrix containing quantum dots. This merging eliminates the need for separate deposition steps and interfaces, simplifying the fabrication process while maintaining well-defined device structure through the integrated layer design.
Solution Approach 2:
The cross-linkable organic material in the combined layer performs multiple functions simultaneously: charge transport, structural support, and emission enhancement. This multi-functional material replaces what would traditionally require separate specialized layers, reducing fabrication complexity while maintaining the structural definition needed for device operation.
3Illumination intensity
If quantum dot concentration is increased to improve emission intensity, then light-emitting efficiency increases, but uniformity of the emissive layer decreases
Solution Approach 1:
The cross-linkable organic material acts as an intermediary matrix that disperses and stabilizes quantum dots at high concentrations. This matrix prevents quantum dot aggregation and settling by providing steric and electrostatic stabilization, enabling high quantum dot loading while maintaining uniform distribution. The cross-linking network further locks in this uniform distribution, preventing phase separation during device operation.
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 CCTEL enhances the performance of quantum dot light-emitting devices by improving light-emitting efficiency and simplifying the fabrication process, allowing for more stable and uniform emission layers, especially in high-resolution multicolor displays.
Implementation Method 1
the crosslinking of the cross-linkable material with the quantum dots dispersed therein to form a crosslinked emissive layer
Implementation Method 2
WO 2017/117994 (Li et al., published Jul. 13, 2017) describes that through external energy stimuli (e.g. pressure, temperature or UV irradiation), QDs which emit different colors can be selectively attached to bonding surfaces
Implementation Method 3
When a forward bias is applied between the anode and cathode, holes and electrons are transported in the device through the hole transport layer and electron transport layer, respectively. The holes and electrons recombine in the emissive material layer, which generates light that is emitted from the device.
Implementation Method 4
Surfaces and ligands of QDs must contain particular ending functional groups (e.g. alkenes, alkynes, thiols) to be selectively strongly bonded to each other through chemical reactions
Implementation Method 5
U.S. Pat. No. 7,910,400 (Kwon et al., issued Mar. 22, 2011) describes that QD films can be made more uniform using wet-type film exchanging ligand processes, in which QDs can be connected to each other using organic ligands with particular functional groups at both ends
Data Source
AI summary
A light-emitting device includes an anode, a cathode, and a crosslinked emissive layer disposed between the anode and the cathode in which quantum dots are dispersed. The crosslinked layer includes a crosslinked material and quantum dots dispersed in the crosslinked mater, the quantum dots having ligands respectively bonded to the quantum dots. The quantum dots are distributed unevenly within the crosslinked material. The ligands have a concentration relative to the weight of the quantum dots of 10 to 45 wt %. A method of forming a crosslinked emissive layer of a light-emitting device in which quantum dots are dispersed includes the steps of depositing a mixture on a deposition surface and subjecting at least a portion of the mixture to an activation stimulus to crosslink the cross-linkable material.