Fluorescent Light-Emitting Layer Structure for Triplet Energy Blocking
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Solution Overview
Problem
Existing light-emitting devices using fluorescent materials face challenges in achieving high emission efficiency and reliability due to inefficient conversion of triplet excitation energy into singlet excitation energy, leading to decreased luminance and reliability.
Innovation Solution
A light-emitting device structure is proposed, featuring a first light-emitting layer with a phosphorescent material that converts triplet excitation energy into light emission, and a second light-emitting layer with a fluorescent material having a luminophore and multiple protecting groups, which inhibits triplet excitation energy transfer to the fluorescent material, thereby enhancing emission efficiency and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fluorescent material is used as the light-emitting substance, then the stability of the compound is improved, but the emission efficiency is worsened due to inefficient conversion of triplet excitation energy into singlet excitation energy
Solution Approach 1:
A TADF material is introduced as an intermediary substance between the electrodes and the fluorescent material. The TADF material first absorbs triplet excitation energy, then converts it to singlet excitation energy through reverse intersystem crossing, and finally transfers this energy to the fluorescent material which emits light. This mediator resolves the contradiction by enabling efficient triplet-to-singlet conversion while maintaining fluorescent material stability.
Solution Approach 2:
The invention modifies the energy level parameters of the light-emitting system by selecting a TADF material with specific triplet and singlet energy levels that are optimized for energy transfer to the fluorescent material. By controlling the triplet excitation energy level and singlet excitation energy level parameters, the system achieves both high conversion efficiency and material stability.
2Loss of energy
If a phosphorescent material is used to convert triplet excitation energy into light emission, then the emission efficiency is improved, but the device complexity increases due to the need for additional materials and processes
Solution Approach 1:
The TADF material performs multiple functions: it acts as a host material for charge recombination, converts triplet excitation energy to singlet excitation energy, and serves as an energy transfer donor to the fluorescent material. This multi-functionality reduces the need for separate phosphorescent materials and simplifies the overall device structure while maintaining high emission efficiency.
3Illumination intensity
If the concentration of fluorescent material is increased to improve light emission, then the luminance is improved, but the triplet excitation energy transfer to fluorescent material increases causing energy loss
Solution Approach 1:
The TADF material serves as an intermediary that prevents direct triplet-to-triplet energy transfer between the host and fluorescent material. Instead, the TADF material absorbs triplet energy, converts it to singlet energy, and then transfers singlet energy to the fluorescent material. This intermediary mechanism allows higher fluorescent material concentrations for improved luminance without the harmful direct triplet energy transfer that causes energy loss.
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 proposed structure significantly improves the emission efficiency and reliability of light-emitting devices by effectively converting triplet excitation energy into singlet excitation energy, leading to enhanced luminance and reduced power consumption.
Implementation Method 1
light emission from the triplet excited state is referred to as phosphorescence
Implementation Method 2
light emission from the singlet excited state is referred to as fluorescence
Implementation Method 3
a singlet excited state is generated from a triplet excited state by reverse intersystem crossing
Implementation Method 4
light-emitting devices utilizing electroluminescence (EL)
Data Source
AI summary
A light-emitting device with high emission efficiency and reliability is provided. The light-emitting device includes first and second fluorescent light-emitting layers. A host material used in the first fluorescent light-emitting layer has a function of converting triplet excitation energy into light emission, a guest material used in the first light-emitting layer has a molecular structure including a luminophore and a protecting group, and one molecule of the guest material includes five or more protecting groups. The introduction of the protecting groups into the molecule inhibits transfer of triplet excitation energy by the Dexter mechanism from the host material to the guest material. An alkyl group or a branched-chain alkyl group is used as the protecting groups. The materials are selected such that the triplet excitation energy level of the host material in the second light-emitting layer is lower than the triplet excitation energy level of the guest material in the second light-emitting layer.