OLED Green Emission Layer Using TADF Sensitization for Color Purity
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Solution Overview
Problem
Existing green light organic electroluminescent devices using phosphorescent materials have wide half-peak widths, leading to low color purity and smaller display color gamut areas due to the heavy atom effect and spin-orbit coupling, limiting their efficiency and color purity.
Innovation Solution
An organic electroluminescent device utilizing a thermally activated delayed fluorescence (TADF) sensitizer and a green fluorescent dye with a specific boron-nitrogen resonance structure, combined with a host material, to achieve narrow emission spectra and high color purity, employing a mass ratio of 0.1% to 30% for the dye and 1% to 99% for the sensitizer in the light-emitting layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphorescent materials are used in green light organic electroluminescent devices, then the device efficiency is improved, but the half-peak width becomes wide, resulting in low color purity and smaller display color gamut area
Solution Approach 1:
The patent changes the emission mechanism from phosphorescence to thermally activated delayed fluorescence (TADF), fundamentally altering the physical process governing light emission. This parameter change enables narrow emission spectra (half-peak width of 10-45 nm) while maintaining high device efficiency, as the TADF mechanism allows for efficient triplet exciton utilization without the heavy atom effect that broadens phosphorescent emission bands
Solution Approach 2:
The patent introduces a TADF sensitizer as an intermediary component in the light-emitting layer. The sensitizer receives energy from the host material and transfers it to the fluorescent dye through a TADF mechanism, acting as a mediator that enables efficient energy transfer while producing narrow emission spectra. This intermediary approach allows the system to achieve both high efficiency and high color purity that cannot be obtained with direct phosphorescent emission
2Use of energy by moving object
If phosphorescent materials are used, then the internal quantum efficiency limit of 25% is broken, but the spectrum width increases, reducing color purity
Solution Approach 1:
The patent changes the emission mechanism from phosphorescence to thermally activated delayed fluorescence (TADF), fundamentally altering the physical process governing light emission. This parameter change enables narrow emission spectra (half-peak width of 10-45 nm) while maintaining high device efficiency, as the TADF mechanism allows for efficient triplet exciton utilization without the heavy atom effect that broadens phosphorescent emission bands
Solution Approach 2:
The patent employs a composite light-emitting layer comprising host material, TADF sensitizer, and fluorescent dye. This composite material system combines the advantages of each component: the host provides structural framework, the TADF sensitizer enables efficient triplet exciton management with narrow emission, and the fluorescent dye contributes to the overall emission characteristics. The composite approach achieves both high internal quantum efficiency and high color purity simultaneously
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 device achieves green light emission with a half-peak width of 10 to 45 nm, improving color purity and efficiency comparable to phosphorescent devices, thereby increasing the display color gamut area.
Implementation Method 1
the triplet state energy thereof returns to the singlet state through the reverse intersystem crossing (RISC) process
Implementation Method 2
the energy is transferred to the doped fluorescent dye to emit light
Data Source
AI summary
The organic electroluminescent device includes a first electrode, a second electrode and an organic layer located between the first electrode and the second electrode, the organic layer includes a light-emitting layer, the light-emitting layer includes a host material, a thermally activated delayed fluorescence sensitizer and a green fluorescent dye, the green fluorescent dye includes a structure as shown in formula I. A thermally activated sensitized fluorescence technique is used, and the green fluorescent dye of a specific structure in combination with the sensitizer and the host material is used, so as to achieve the effects of narrowing the spectrum of a device and improving the green color purity. The efficiency of the organic electroluminescent device is equivalent to that of a phosphorescent green light device, so that a display panel including the organic electroluminescent device has a large display color gamut area.