Quantum Dot Light-Emitting Device Using TADF Energy Transfer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The poor injection ability of holes into quantum dots due to their valence band being far below the highest occupied molecular orbital (HOMO) level of the hole transport layer leads to carrier imbalance, current leakage, and degradation in quantum dot light-emitting devices, affecting their light-emitting efficiency and lifetime.
Innovation Solution
Incorporating a thermally activated delayed fluorescence (TADF) material as a fluorescent layer between the electrodes, which can be codoped with the quantum dot light-emitting material or form an energy transfer layer, enhancing energy transfer and improving the internal quantum efficiency by converting triplet excitons into singlet excitons through reverse intersystem crossing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct injection of carriers is used to excite quantum dots, then the device structure is simple, but the hole injection ability is poor due to valence band mismatch leading to carrier imbalance and current leakage
Solution Approach 1:
The patent introduces an energy transfer layer comprising a thermally activated delayed fluorescence (TADF) material as an intermediary between the hole transport layer and quantum dot light-emitting layer. This TADF layer acts as a mediator that receives excitons from the hole transport layer and transfers energy to the quantum dots, bypassing the direct carrier injection problem caused by valence band mismatch. The TADF material's triplet state to singlet state transition enables efficient energy transfer to quantum dots without requiring direct hole injection into the quantum dot valence band.
2Reliability
If energy transfer mechanism is used to excite quantum dots, then the carrier injection problem is avoided, but the internal quantum efficiency is limited due to triplet exciton loss
Solution Approach 1:
The patent utilizes the unique photophysical parameters of TADF materials, specifically the small energy difference between triplet and singlet states (ΔEST), to enable reverse intersystem crossing. By selecting TADF materials with appropriate energy level parameters that match both the hole transport layer and quantum dots, the system achieves efficient energy transfer while converting non-emissive triplet excitons into emissive singlet excitons, thereby significantly improving internal quantum efficiency.
Solution Approach 2:
The patent employs a composite energy transfer system where the TADF material is combined with the hole transport layer and quantum dot light-emitting layer. This composite structure creates a multi-functional system that simultaneously achieves good hole extraction, efficient energy transfer, and high internal quantum efficiency by leveraging the complementary properties of each material component.
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 approach enhances the light-emitting ability of quantum dots by ensuring efficient energy transfer, potentially reaching 100% internal quantum efficiency and improving the overall performance and longevity of quantum dot light-emitting devices.
Implementation Method 1
converting triplet excitons into singlet excitons through reverse intersystem crossing
Implementation Method 2
a fluorescent material between the first electrode layer and the second electrode layer, wherein the fluorescent material comprises a thermally activated delayed fluorescence material
Implementation Method 3
injection of holes from a hole transport layer to a quantum dot light-emitting layer, and injection of electrons from an electron transport layer to the quantum dot light-emitting layer, and combining the holes and the electrons in the quantum dot light-emitting layer to form excitons and emit light
Implementation Method 4
Due to quantum confinement of the electrons and holes, the continuous band structure becomes a discrete energy level structure with molecular characteristics, and the quantum dots can be excited to emit fluorescence
Data Source
Figure 1~4
Figure 5
AI summary
A quantum dot light-emitting device, a fabricating method thereof, a display substrate and a display apparatus are provided. The quantum dot light-emitting device includes: a base substrate; a first electrode layer, a light-emitting layer, a second electrode layer and an encapsulation layer which are sequentially formed on the base substrate, wherein the light-emitting layer includes a quantum dot light emitting material; a fluorescent material is disposed between the first electrode layer and the second electrode layer, and the fluorescent material includes a thermally activated delayed fluorescence (TADF) material; one of the first electrode layer and the second electrode layer is an anode layer, and the other of the first electrode layer and the second electrode layer is a cathode layer.