Quantum Dot Salt Ligands for Charge Transport
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Solution Overview
Problem
Quantum dots in quantum dot light-emitting diodes (QD-LEDs) do not reach maximum theoretical efficiency due to crystal defects and the insulating, bulky nature of ligands, which hinder charge transport and packing in the solid state.
Innovation Solution
Incorporating salt ligands with charge transporting properties at the surface of quantum dots, allowing for cross-linkable cations that enhance charge transport and solubility, and using a combination of ligands to balance charges and stabilize the system, enabling efficient packing and defect coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ligands are used to passivate crystal defects, then quantum efficiency is improved, but charge transport is hindered due to insulating and bulky nature of ligands
Solution Approach 1:
The patent changes the chemical parameters of the ligands by using salt ligands with ionic character instead of conventional organic ligands. This parameter change transforms the insulating ligands into charge-transporting ligands, resolving the contradiction between defect passivation and charge transport
Solution Approach 2:
The patent employs composite ligand structures consisting of both anionic and cationic components. The anionic part provides defect passivation while the cationic part enables charge transport, combining the beneficial properties of different materials within a single ligand system
2Productivity
If small ligands are used to achieve better packing of quantum dots, then carrier mobility is improved, but crystal defects are not adequately passivated
Solution Approach 1:
The patent divides the ligand into two functional segments: an anionic segment that passivates crystal defects and a cationic segment that facilitates charge transport. This segmentation allows each part to perform its specific function optimally, resolving the contradiction between packing efficiency and defect passivation
Solution Approach 2:
The salt ligand performs multiple functions simultaneously: it acts as a passivating agent for crystal defects, a charge transport medium, and a packing optimizer. This multi-functionality resolves the contradiction by making a single ligand type capable of addressing multiple competing requirements
3Productivity
If ligands are exchanged after quantum dot synthesis, then solubility and packing are improved, but quantum efficiency is reduced due to additional processing steps
Solution Approach 1:
The patent performs ligand exchange during the quantum dot synthesis process itself, rather than as a subsequent step. This preliminary action ensures that the salt ligands are already in place to maintain quantum efficiency while providing the desired packing and solubility properties
Solution Approach 2:
The patent merges the synthesis process with the ligand exchange process, combining two previously separate operations into a single integrated process. This merging eliminates the need for additional processing steps that would compromise quantum efficiency while achieving the desired packing efficiency
Data Source
AI summary
A quantum dot includes a salt ligand at an outer surface thereof, the salt ligand including an anion and a cation, the cation having charge transporting properties. A light-emitting device includes an anode, a cathode, and an emissive layer disposed between the anode and the cathode, the emissive layer including multiple instances of the quantum dot. In some embodiments, the emissive layer is a crosslinked layer formed by depositing a mixture including the quantum dots on a layer, and subjecting at least a portion of the mixture to external activation stimuli to form the emissive layer including quantum dots dispersed in a crosslinked matrix.