Organic EL Dual Emitting Layer Triplet-Triplet Annihilation
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Solution Overview
Problem
Existing organic electroluminescence devices face limitations in luminous efficiency due to the inefficiency of triplet exciton utilization, with conventional devices having a theoretical internal quantum efficiency of 25% due to the thermal deactivation of triplet excitons, and struggles in achieving improved performance in top emission type devices with color conversion portions.
Innovation Solution
The organic electroluminescence device incorporates a dual emitting layer structure with host materials having specific triplet energy relationships and photoluminescence spectrum overlaps, where the first emitting layer generates triplet excitons and the second emitting layer utilizes the Triplet-Triplet Annihilation (TTA) mechanism to enhance singlet exciton generation, improving luminous efficiency by minimizing light extraction losses through controlled emission spectrum overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single emitting layer is used, then the device structure is simple, but the internal quantum efficiency is limited to 25% due to thermal deactivation of triplet excitons
Solution Approach 1:
The emitting layer is divided into two distinct layers: a first emitting layer containing host material H1 and emitting material E1, and a second emitting layer containing host material H2 and emitting material E2. This segmentation allows the first layer to generate triplet excitons while the second layer utilizes TTA to convert them to singlet excitons for light emission, thereby resolving the efficiency limitation of conventional single-layer structures.
Solution Approach 2:
The first emitting layer acts as an intermediary that generates triplet excitons which are then transferred to the second emitting layer. The triplet energy relationship T1(H1) > T1(H2) ensures thermodynamic feasibility of this energy transfer, enabling efficient triplet exciton utilization without requiring direct electron-hole recombination in the second layer.
2Loss of energy
If the photoluminescence spectra of the two emitting layers are made to overlap significantly, then light extraction losses are minimized, but the spectral design precision requirements increase
Solution Approach 1:
The patent specifies precise parameters for photoluminescence spectrum overlap, requiring that the maximum peak wavelengths λ1 and λ2 satisfy |λ1-λ2| ≤ 3 nm and the FWHM values satisfy |FWHM1-FWHM2| ≤ 2 nm, or alternatively that the overlap integral of normalized spectra be 99.0% or more. These parameter specifications enable minimal light extraction loss while providing clear design criteria for material selection and device fabrication.
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 configuration enhances luminous efficiency by effectively utilizing triplet excitons through TTA, improving internal quantum efficiency beyond conventional limits and reducing light extraction losses, particularly in top emission type devices with color conversion, thereby enhancing overall performance.
Implementation Method 1
a phenomenon in which a singlet exciton is generated by collision and fusion of two triplet excitons (hereinafter, occasionally referred to as a Triplet-Triplet Fusion (TTF) phenomenon)
Implementation Method 2
When voltage is applied to an organic EL device, holes are injected from an anode and electrons are injected from a cathode into an emitting layer. The injected holes and electrons are recombined in the emitting layer to form excitons.
Implementation Method 3
a maximum peak wavelength λ1 and a full width at half maximum FWHM1 of a photoluminescence spectrum of a first film provided by adding the first emitting material to the first host material
Data Source
AI summary
An organic EL device includes an anode, an emitting layer of first and second emitting layers, and a cathode. The first emitting layer contains a first host material and a first emitting material. The second emitting layer contains a second host material and a second emitting material. The first and second emitting materials emit light having a maximum peak wavelength of 500 nm or less. The triplet energy of the first host material T1(H1) and the triplet energy of the second host material T1(H2) satisfy T1(H1)>T1(H2). The maximum peak wavelength λ1 and FWHM1 of a first film provided by adding the first emitting material to the first host material, and the maximum peak wavelength λ2 and FWHM2 of a second film provided by adding the second emitting material to the second host material satisfy |λ1−λ2|≤3 nm and |FWHM1−FWHM2|≤2 nm.