Green OLED Composite Emission Layer for BT-2020 Color Purity
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Solution Overview
Problem
Existing organic electroluminescent devices struggle to achieve a balance of high quantum yield, long lifetime, and good color purity, particularly in achieving the BT-2020 and DCPI3 color gamut, which requires a narrow emission spectrum.
Innovation Solution
Incorporating a light-emitting layer with a host material, a thermally activated delayed fluorescence (TADF) material, and a small full width at half maximum (FWHM) emitter, where the TADF material transfers energy to the FWHM emitter, resulting in a narrow green emission with an emission maximum of 500 nm to 560 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional OLED device uses standard emitters, then it can achieve good efficiency and lifetime, but it cannot achieve good color purity and narrow emission spectrum required for BT-2020 and DCPI3 color gamut
Solution Approach 1:
The patent employs a composite light-emitting layer containing both TADF emitter and NRCT emitter materials. The TADF emitter (e.g., carbazole derivative) provides efficient triplet exciton utilization with broad emission, while the NRCT emitter (e.g., pyridine-boron-dipyrromethene complex) provides narrow emission spectrum. The synergistic combination allows the device to achieve both high efficiency and narrow emission spectrum for BT-2020 color gamut compliance.
2Manufacturing precision
If an OLED device targets BT-2020 and DCPI3 color gamut with narrow emission spectrum, then color purity is improved, but efficiency and lifetime are compromised
Solution Approach 1:
The patent optimizes the energy level parameters of the host and emitter materials to ensure efficient energy transfer. The host material (e.g., mCP or TCTA) is selected with triplet energy level (ET) higher than both TADF and NRCT emitters, while the TADF emitter has higher triplet energy than the NRCT emitter. This parameter optimization enables efficient triplet exciton transfer from host to TADF to NRCT, achieving high external quantum efficiency (>10% at 1000 cd/m²) and extended device lifetime (>100 h at constant current density).
3Use of energy by moving object
If a device uses TADF material alone, then efficiency is improved through triplet exciton utilization, but emission spectrum becomes too broad for BT-2020 color gamut
Solution Approach 1:
The TADF emitter serves as an energy transfer intermediary between the host material and the NRCT emitter. The host transfers triplet excitons to the TADF emitter, which then transfers energy to the NRCT emitter. This intermediary mechanism allows efficient utilization of triplet excitons (improving quantum yield) while the final emission comes from the narrow-spectrum NRCT emitter, achieving both high efficiency and color purity.
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 combination achieves a long lifetime, high quantum yield, and narrow emission suitable for the BT-2020 and DCPI3 color gamut, with external quantum efficiencies exceeding 10% at 1000 cd/m² and lifetimes exceeding 100 h at a constant current density.
Implementation Method 1
at least one thermally activated delayed fluorescence (TADF) material E B, wherein the TADF material E B transfers energy to the small FWHM emitter S B
Implementation Method 2
The different layers are sequentially disposed. Excitons of high energy are then generated by recombination of the holes and the electrons in the light-emitting layer. The decay of such excited states (e.g., singlet states such as S1 and/or triplet states such as T1) to the ground state (S0) desirably leads to the emission of light.
Data Source
AI summary
The present invention relates to a an organic electroluminescent device comprising at least one light-emitting layer B comprising at least one host material HB, at least one thermally activated delayed fluorescence (TADF) material EB, and at least one small full width at half maximum (FWHM) emitter SB wherein E B transfers energy to SB and SB emits light with an emission maximum in the wavelength range from 500 nm to 560 nm.