Quantum Dot Light-Emitting Element with Bandgap-Engineered Shells
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Solution Overview
Problem
The light-emitting layer of existing light-emitting elements containing non-light-emitting quantum dots impairs electron and hole transport capabilities, leading to reduced light emission efficiency in terms of luminance and external quantum efficiency (EQE).
Innovation Solution
A light-emitting element with a light-emitting layer comprising first and second quantum dots, where the first quantum dots have a core-shell structure with a shell containing S or Se, and the second quantum dots have a core-shell structure with a shell containing Te, ensuring a conduction band minimum (CBM) of the first shell is lower than that of the second shell, and a valence band maximum (VBM) of the first shell is lower than that of the second shell, optimizing carrier balance and recombination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-light-emitting quantum dots are added to the light-emitting layer, then the quantum dot density is increased, but the electron transport capability and hole transport capability are impaired, leading to reduced light emission efficiency
Solution Approach 1:
The quantum dots are divided into two distinct groups: first quantum dots with S or Se shells and second quantum dots with Te shells. This segmentation allows each group to perform specialized functions - the first quantum dots primarily for light emission while the second quantum dots facilitate carrier transport, thereby maintaining high quantum dot density without compromising light emission efficiency
Solution Approach 2:
Different shell materials are assigned to different quantum dot groups based on their specific functions. The S or Se shell in first quantum dots optimizes for light emission properties, while the Te shell in second quantum dots optimizes for carrier transport capability. This local differentiation of material properties enables simultaneous optimization of both light emission efficiency and carrier transport
2Reliability
If quantum dots with higher CBM and VBM are used, then the shell material properties are improved, but electron flow into the hole transport layer increases, reducing carrier balance
Solution Approach 1:
The second quantum dots with Te shells act as intermediary carriers that facilitate controlled electron and hole transport. These intermediary quantum dots mediate the carrier flow between the first quantum dots and the transport layers, preventing direct excessive electron flow into the hole transport layer while maintaining optimal carrier balance through their specific CBM and VBM energy levels
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
This configuration enhances light emission efficiency by improving carrier balance, reducing electron flow into the hole transport layer, and increasing the chances of recombination in the first quantum dots, thereby enhancing luminance and EQE.
Implementation Method 1
wherein a CBM of the first shell is lower than a CBM of the second shell, and a VBM of the first shell is lower than a VBM of the second shell
Implementation Method 2
A light-emitting element includes: an anode; a cathode provided across from the anode; and a light-emitting layer provided between the anode and the cathode
Data Source
AI summary
A light-emitting element includes: an anode; a cathode provided across from the anode; and a light-emitting layer provided between the anode and the cathode, and containing first quantum dots and second quantum dots, the first quantum dots each having a core-shell structure including a first core and a first shell provided on a surface of the first core, and the second quantum dots each having a core-shell structure including a second core and a second shell provided on a surface of the second core. A CBM of the first shell is lower than a CBM of the second shell, and a VBM of the first shell is lower than a VBM of the second shell.