CdZnSe Core CdZnS Shell Blue Quantum Dots
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing blue quantum dots have a deep HOMO energy level and high LUMO energy level due to a thick ZnS shell, leading to poor carrier injection and short device lifetime, which fails to meet commercialization requirements, especially at low current densities.
Innovation Solution
A quantum dot with a CdZnSe core and a CdZnS shell, where the molar ratio of Cd to S in the shell layer is between 0.15:1 and 0.4:1, facilitating better energy matching with transport layers for improved carrier injection, and a preparation method involving controlled precursor addition and reaction conditions to form a homogeneous shell layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thick ZnS shell is used to cover blue quantum dots, then the quantum dots achieve high brightness (>10,000 cd/m2) and initial external quantum efficiency (>10%), but the HOMO energy level becomes too deep and LUMO energy level becomes too high, resulting in poor carrier injection and device lifetime <1000 hours
Solution Approach 1:
The patent changes the material composition parameter of the shell layer by using CdZnS alloy instead of pure ZnS, and specifically controlling the Cd:S molar ratio to be between 0.15:1 and 0.4:1. This parameter change adjusts the energy levels (HOMO and LUMO) to achieve better carrier injection while maintaining high brightness, resolving the contradiction between initial efficiency and device lifetime
Solution Approach 2:
The patent employs a composite shell layer made of CdZnS alloy material that combines the advantages of both CdS (low LUMO level for electron injection) and ZnS (high brightness stability). This composite material approach allows the shell to simultaneously provide good carrier injection and maintain high brightness, thereby extending device lifetime while preserving initial efficiency
2Reliability
If ZnCdSe quantum dots are coated with ZnSe shell to improve HOMO level and achieve device lifetime of 7000 hours, then the energy level matching with hole transport layer is improved, but the external quantum efficiency attenuates to only 3% at luminance of 50-200 cd/m2, which is far below commercialization requirements
Solution Approach 1:
The patent changes the shell material from ZnSe to CdZnS alloy and specifically controls the Cd:S molar ratio parameter to be between 0.15:1 and 0.4:1. This parameter optimization achieves a balance where the LUMO level is lowered to improve electron injection and maintain high external quantum efficiency (9.6%-12.6% at low current density) while the HOMO level remains suitable for hole injection, thus achieving both long lifetime and high efficiency
Solution Approach 2:
The patent applies different material compositions to different functional requirements: the CdZnS shell layer with optimized Cd:S ratio provides low LUMO level for electron injection, while the core-shell structure maintains appropriate HOMO level for hole injection. This local optimization of material properties at different locations (shell vs core, electron transport interface vs hole transport interface) achieves both long device lifetime and high external quantum efficiency simultaneously
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 quantum dot achieves higher external quantum efficiency and longer device lifetime at lower working current densities, meeting commercialization requirements for blue QLEDs with maximum EQE ranging from 9.6% to 12.6% and extended lifespan.
Implementation Method 1
The CdZnSe core and CdZnS shell layer structure achieves energy level matching with transport layer materials, where the HOMO level of the quantum dot aligns with the HOMO level of the hole transport layer (TFB), facilitating effective carrier injection
Implementation Method 2
The optimized energy level structure enables effective carrier injection from the transport layers into the quantum dot, with holes injecting from the TFB hole transport layer and electrons from the electron transport layer
Implementation Method 3
The quantum dot exhibits photoluminescence emission in the blue region with a peak wavelength of 460-480 nm, making it suitable for blue light emission in photoelectric devices
Data Source
AI summary
The present disclosure relates to a quantum dot and a preparation method for the same, and a photoelectric device. The quantum dot includes a core and a shell layer coating the core, a material of the core is CdZnSe, and a material of the shell layer is CdZnS, wherein, a molar ratio of Cd element with respect to S element in the shell layer is from 0.15:1 to 0.4:1.