Green OLED Emission Layer With TADF for Narrow FWHM and Lifetime
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Solution Overview
Problem
Existing organic electroluminescent devices struggle to achieve a balance of high efficiency, long lifetime, and good color purity, particularly in achieving the BT-2020 and DCPI3 color gamut, due to broad emission spectra and the use of expensive transition metal-based phosphorescence materials.
Innovation Solution
Incorporating a light-emitting layer with a TADF material and a small full width at half maximum (FWHM) emitter, along with a host material and an exciton management layer containing a triplet-triplet-annihilation material, to manage excitons and enhance emission efficiency and color purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescence materials based on transition metals are used, then efficiency is improved, but cost increases due to low abundance of materials like iridium
Solution Approach 1:
The patent replaces expensive transition metal-based phosphorescence materials with organic TADF materials that are more abundant and cost-effective. The TADF materials achieve comparable efficiency without relying on scarce metals like iridium, directly addressing the cost issue while maintaining energy efficiency.
Solution Approach 2:
The patent changes the material composition parameters by using specific TADF materials (E B[0012]) with optimized molecular structures and energy levels. This parameter change enables the system to achieve high efficiency through organic materials rather than transition metals, resolving the contradiction between efficiency and cost.
2Use of energy by moving object
If phosphorescence emitters are used, then efficiency is improved, but emission spectrum becomes broad (FWHM > 0.25 eV), leading to high losses in out-coupling efficiency for top emitting devices
Solution Approach 1:
The patent employs TADF materials that inherently provide narrow emission spectra (FWHM ≤ 0.25 eV), replacing phosphorescence emitters that produce broad spectra. This substitution eliminates the out-coupling efficiency losses associated with broad emission while maintaining high efficiency through the TADF mechanism.
Solution Approach 2:
The patent changes the emission spectrum parameter by selecting TADF materials with specific molecular structures that produce narrow FWHM values. This parameter change directly addresses the out-coupling efficiency issue by ensuring the emission spectrum is narrow enough for top-emitting device architecture.
3Illumination intensity
If fluorescence or TADF emitters with narrow emission spectrum are used, then color purity is improved, but efficiency decreases due to roll-off behavior at higher luminance
Solution Approach 1:
The patent uses a composite light-emitting layer combining TADF material E B[0012] with host material H B[0172] and exciton management components. This composite structure maintains the narrow emission spectrum of the TADF emitter while the host and exciton management materials work together to suppress roll-off behavior, thereby preserving both color purity and efficiency at high luminance.
Solution Approach 2:
The patent introduces an exciton management layer with triplet-triplet-annihilation material that acts as an intermediary to manage excitons effectively. This intermediary component prevents exciton-polaron annihilation and exciton-exciton annihilation, thereby maintaining high efficiency at high luminance while the TADF emitter maintains its narrow emission spectrum for good color purity.
4Illumination intensity
If fluorescence or TADF emitters are used, then color purity is improved, but lifetime decreases due to exciton-polaron annihilation and exciton-exciton annihilation
Solution Approach 1:
The patent introduces an exciton management layer containing triplet-triplet-annihilation material that acts as an intermediary to manage excitons before they can cause damage. This intermediary layer prevents exciton-polaron annihilation and exciton-exciton annihilation at the TADF emitter, thereby extending device lifetime while maintaining the narrow emission spectrum required for good color purity.
Solution Approach 2:
The patent places the exciton management layer adjacent to the light-emitting layer to provide beforehand cushioning against exciton-related degradation. This protective layer absorbs and manages excitons before they can cause annihilation events that would reduce device lifetime, allowing the TADF emitter to maintain its narrow emission spectrum without suffering from reduced lifetime.
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 device achieves a long lifetime, high quantum yield, and narrow emission, effectively meeting the BT-2020 and DCPI3 color gamut requirements.
Implementation Method 1
The TADF material E B[0012] comprises a first chemical moiety A B[0010] and a second chemical moiety B B[0011], which are covalently bonded to each other... the TADF material E B[0012] has a lowermost excited singlet state energy level E(S1 E B[0012]) and a lowermost excited triplet state energy level E(T1 E B[0012... displaying reversed intersystem crossing (RISC)
Implementation Method 2
an exciton management layer EXL containing a triplet-triplet-annihilation material... 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
Implementation Method 3
When a voltage (and electrical current) is applied to an organic electroluminescent device, holes and electrons are injected from an anode and a cathode, respectively... Excitons of high energy are then generated by recombination of the holes and the electrons in a light-emitting layer
Implementation Method 4
some fluorescence or thermally-activated-delayed-fluorescence (TADF) emitters have been developed that display a rather narrow emission spectrum, which exhibits an FWHM of the emission spectrum, which is typically smaller than or equal to 0.25 eV
Data Source
AI summary
The present invention relates to organic electroluminescent devices comprising a light-emitting layers B comprising a TADF material, a small full width at half maximum (FWHM) emitter SB emitting green light with an FWHM of less than or equal to 0.25 eV, and a host material HB, and an optional excitation energy transfer component EET-2. Furthermore, the present invention relates to a method for generating green light by means of an organic electroluminescent device according to the present invention.