Light-Emitting Device With Protected Guests Against Dexter Transfer
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Solution Overview
Problem
Existing light-emitting devices face challenges in achieving high emission efficiency and reliability due to inefficient conversion of triplet excitation energy to singlet excitation energy, leading to decreased luminance and reliability, particularly in multicolor devices with phosphorescent and fluorescent layers.
Innovation Solution
Incorporating a first light-emitting layer with a material that converts triplet excitation energy into light emission and a second light-emitting layer with a material that converts singlet excitation energy into light emission, utilizing luminophores or exciplexes with specific protecting groups, and ensuring the emission spectra overlap with absorption spectra to enhance energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent material is used to convert triplet excitation energy into light emission, then emission efficiency is improved, but device stability and reliability deteriorate due to difficulty in developing stable compounds with high triplet excitation energy levels
Solution Approach 1:
The patent changes the emission mechanism parameter from phosphorescence to fluorescence by using fluorescent materials with high triplet energy levels. This allows the device to maintain high emission efficiency through effective triplet energy utilization while achieving improved device stability and reliability, as fluorescent materials do not require heavy metal atoms and have longer operational lifetimes.
Solution Approach 2:
The patent introduces an intermediary mechanism where triplet excitons generated in the fluorescent material are converted to singlet excitons through thermal energy (reverse intersystem crossing), which then emit photons. This intermediary process allows efficient utilization of triplet states while maintaining the stability advantages of fluorescent materials.
2Reliability
If a fluorescent material is used instead of phosphorescent material, then device stability is improved, but emission efficiency deteriorates due to inability to utilize triplet excitation energy
Solution Approach 1:
The patent changes the energy utilization parameter by selecting fluorescent materials with triplet energy levels (T1) higher than their singlet energy levels (S1). This parameter configuration enables the material to accept triplet excitons from host materials and convert them to singlet excitons through thermal energy, thereby achieving high emission efficiency while maintaining device stability.
Solution Approach 2:
The patent utilizes dynamic thermal energy at operating temperatures to drive the reverse intersystem crossing process, converting triplet excitons to singlet excitons in the fluorescent material. This dynamic process enables efficient energy utilization without requiring stable phosphorescent compounds with high triplet energy levels.
3Adaptability or versatility
If multiple light-emitting layers are used in multicolor devices, then color variety is improved, but energy transfer efficiency deteriorates due to deactivation pathways between layers
Solution Approach 1:
The patent applies local quality by assigning different fluorescent materials with specific triplet energy levels to different light-emitting layers. Each layer is designed with materials having appropriate energy level configurations to prevent deactivation pathways, ensuring efficient energy transfer within each layer while maintaining color variety across multiple layers.
Solution Approach 2:
The patent changes the energy level parameters of materials in different light-emitting layers to create energy cascades where higher energy layers transfer to lower energy layers without deactivation. By carefully selecting materials with appropriate T1 and S1 energy level differences, the patent eliminates deactivation pathways and improves overall energy transfer efficiency in multicolor devices.
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 structure improves emission efficiency and reliability by inhibiting deactivation pathways, enhancing fluorescence efficiency, and reducing power consumption in light-emitting devices.
Implementation Method 1
the first material has a function of converting triplet excitation energy into light emission
Implementation Method 2
the second material has a function of converting singlet excitation energy into light emission
Implementation Method 3
the emission spectrum of the third material overlaps with the longest wavelength absorption band in the absorption spectrum of the fourth material
Data Source
AI summary
A light-emitting device with high emission efficiency and reliability is provided. The light-emitting device includes a fluorescent light-emitting layer and a phosphorescent light-emitting layer. A host material used in the fluorescent light-emitting layer has a function of converting triplet excitation energy into light emission and a guest material used in the fluorescent light-emitting layer emits fluorescence. The guest material 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 from the host material to the guest material by the Dexter mechanism. An alkyl group or a branched-chain alkyl group is used as the protecting group. The longest wavelength absorption band in the absorption spectrum of the guest material in the phosphorescent light-emitting layer has an overlap with the emission spectrum of the host material in the phosphorescent light-emitting layer.