TADF Organic EL Device with Host Material
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current organic electroluminescent (EL) devices, particularly blue phosphorescent and fluorescent types, face challenges in achieving high efficiency and long lifetime with low driving voltage, and existing TADF-based devices have limitations in efficiency and stability.
Innovation Solution
An organic EL device incorporating a thermally activated delayed fluorescent material represented by a specific general formula, combined with a host material, in the light-emitting layer to enhance efficiency and stability, with the TADF material having a specific emission wavelength range and ionization potential, and the host material having a higher singlet excitation energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent emission-type organic EL device is used to improve internal quantum efficiency to 100%, then efficiency is improved, but lifetime is insufficient particularly for blue devices
Solution Approach 1:
The patent changes the emission mechanism parameter from phosphorescence to TADF by selecting materials with appropriate singlet-triplet energy gaps. The TADF material (compound 1) has a small energy difference between singlet and triplet states, enabling efficient reverse intersystem crossing and achieving near-100% internal quantum efficiency through delayed fluorescence rather than phosphorescence, thereby improving both efficiency and lifetime.
2Use of energy by moving object
If TADF mechanism is used to improve internal quantum efficiency to 100% theoretically, then efficiency is improved, but lifetime characteristic is insufficient
Solution Approach 1:
The patent uses a composite light-emitting layer containing both TADF material (compound 1) and host material (compound 2 or 3). The host material absorbs excitons and transfers energy to the TADF material, which then emits light through delayed fluorescence. This composite approach enables efficient energy utilization with near-100% internal quantum efficiency while the host-guest system provides improved stability and lifetime compared to pure TADF materials.
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 high luminous efficiency, long lifetime, and low driving voltage, with improved color purity and stability, outperforming existing TADF-based devices in efficiency and lifetime characteristics.
Implementation Method 1
The TADF mechanism utilizes a phenomenon in which inverse intersystem crossing from a triplet exciton to a singlet exciton occurs in a material having a small energy difference between a singlet level and a triplet level
Implementation Method 2
inverse intersystem crossing from a triplet exciton to a singlet exciton
Implementation Method 3
the host material having a higher singlet excitation energy
Implementation Method 4
When a voltage is applied to an organic EL device, a hole is injected from an anode into a light-emitting layer, and an electron is injected from a cathode into the layer
Data Source
AI summary
Provided is a thermally activated delayed fluorescent organic electroluminescent device having a low driving voltage, high luminous efficiency, and a long lifetime. The organic electroluminescent device includes light-emitting layers between an anode and a cathode opposite to each other, and at least one of the light-emitting layers contains a thermally activated delayed fluorescent material, or the thermally activated delayed fluorescent material and a host material. The thermally activated delayed fluorescent material is represented by the following general formula (1) where A represents an electron-withdrawing group, such as a CN group, and D1 and D2 each represent an electron-donating group having an indole ring structure.