Light-Emitting Element with Protecting Groups for Multicolor Emission
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Solution Overview
Problem
Current light-emitting elements using fluorescent materials face challenges in efficiently converting triplet excitation energy into singlet excitation energy, leading to decreased emission efficiency, especially in achieving multicolor emission from a single layer without the need for multiple stacked layers.
Innovation Solution
A light-emitting element structure incorporating a first material that converts triplet excitation energy into light emission and a second material with protecting groups that efficiently transfers singlet excitation energy, utilizing a luminophore with condensed aromatic or heteroaromatic rings and specific protecting groups to inhibit Dexter mechanism energy transfer, allowing for multicolor emission from a single layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fluorescent material is used in a light-emitting element, then the compound stability is improved, but the emission efficiency deteriorates due to inability to utilize triplet excited state energy
Solution Approach 1:
A TADF material is introduced as an intermediary substance between the electrode and the fluorescent material. This TADF material has the capability to convert triplet excited state energy into singlet excited state energy through reverse intersystem crossing, which then transfers energy to the fluorescent material for light emission. This mediator resolves the contradiction by enabling efficient energy utilization while maintaining fluorescent material stability.
Solution Approach 2:
The invention changes the energy level parameters of the light-emitting layer by incorporating a TADF material with specific energy characteristics (small S1-T1 energy gap). This parameter change enables efficient reverse intersystem crossing from triplet to singlet state, allowing the system to utilize triplet excited state energy that would otherwise be lost, thereby improving emission efficiency while maintaining fluorescent material stability.
2Adaptability or versatility
If multiple stacked EL layers are used to achieve multicolor emission, then the color variety is improved, but the device complexity increases
Solution Approach 1:
The invention merges the functions of multiple EL layers into a single light-emitting layer by co-doping both TADF material and fluorescent material together. The TADF material converts triplet excited state energy to singlet excited state energy, which then transfers to different fluorescent materials to produce multiple colors. This combining approach achieves multicolor emission in one layer, reducing device complexity while maintaining color variety.
Solution Approach 2:
The TADF material serves multiple functions simultaneously: it acts as a host for the fluorescent material, converts triplet excited state energy to singlet excited state energy, and enables energy transfer to multiple different fluorescent materials to produce various colors. This multi-functionality allows a single light-emitting layer to achieve what would otherwise require multiple stacked layers, simplifying the device structure.
3Illumination intensity
If the concentration of fluorescent material is increased to improve emission intensity, then the brightness is improved, but the energy transfer efficiency from TADF material deteriorates
Solution Approach 1:
The invention uses a moderate concentration of fluorescent material (0.01-5 wt%) rather than high concentration, which is sufficient to achieve good emission intensity while preventing excessive concentration quenching. This partial action approach maintains optimal energy transfer efficiency from the TADF material to the fluorescent material, avoiding the energy loss that would occur at higher concentrations where fluorescent molecules quench each other's excitation.
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 emission efficiency and reliability by effectively converting triplet excitation energy into singlet excitation energy, enabling multicolor light emission from a single light-emitting layer with reduced power consumption and increased stability.
Implementation Method 1
In a TADF material, a singlet excited state is generated from a triplet excited state by reverse intersystem crossing
Implementation Method 2
light emission from the singlet excited state is referred to as fluorescence
Implementation Method 3
utilizing a luminophore with condensed aromatic or heteroaromatic rings and specific protecting groups to inhibit Dexter mechanism energy transfer
Implementation Method 4
light emission from the triplet excited state is referred to as phosphorescence
Data Source
AI summary
A light-emitting element with high emission efficiency and high reliability is provided. The light-emitting element includes a light-emitting layer that contains a material serving as an energy donor and a light-emitting material. The material serving as an energy donor has a function of converting triplet excitation energy into light emission and the light-emitting material emits fluorescence. The light-emitting material has a molecular structure that includes a luminophore and protecting groups; one molecule of a guest material includes 5 or more protecting groups. Introduction of protecting groups in a molecule inhibits the energy transfer of triplet excitation energy from the material serving as an energy donor to the light-emitting material by the Dexter mechanism. An alkyl group or a branched-chain alkyl group is used as the protecting group. Light emission is obtained from both the light-emitting material and the material serving as an energy donor.