Organic Electroluminescence Device Azine Blocking Layer Triplet Confinement
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Solution Overview
Problem
Conventional organic electroluminescence devices face limitations in achieving high efficiency due to the inefficient utilization of triplet excitons, particularly in fluorescent emission, where the theoretical limit of internal quantum efficiency is 25% and external quantum efficiency is low, especially for blue-emission devices.
Innovation Solution
Incorporating an aromatic heterocyclic derivative with an azine ring in the blocking layer, which has a higher triplet energy than the host, to facilitate the Triplet-Triplet Fusion (TTF) phenomenon, enhancing the supply of electrons to the emitting layer and increasing the luminous efficiency by confining triplet excitons and promoting their collision to generate singlet excitons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional fluorescent EL devices are used, then the device structure is simple, but the external quantum efficiency is limited to about 5-8%
Solution Approach 1:
The electron transporting zone is divided into two functional layers: a blocking layer adjacent to the emitting layer and an electron injecting layer adjacent to the cathode. This segmentation allows the blocking layer to specifically manage triplet excitons and promote TTF phenomenon while the electron injecting layer handles electron supply, thereby resolving the contradiction between simple structure and low efficiency by adding only one functional layer rather than completely redesigning the device.
Solution Approach 2:
The blocking layer acts as an intermediary between the emitting layer and the electron injecting layer. It mediates the interaction between triplet excitons and electrons by confining triplet excitons in the emitting layer and facilitating their collision with electrons, thereby enabling the TTF phenomenon to occur efficiently. This intermediary layer resolves the contradiction by providing a specific functional interface that enhances efficiency without requiring complete structural overhaul.
2Loss of energy
If triplet excitons are utilized through TTF phenomenon, then the external quantum efficiency can be improved, but the device requires additional blocking layer with specific triplet energy requirements
Solution Approach 1:
The invention specifies that the blocking layer should have a triplet energy (ETb) larger than the triplet energy (ETh) of the host material in the emitting layer. This parameter change in the blocking layer's triplet energy enables it to confine triplet excitons effectively and promote the TTF phenomenon. By controlling this specific energy parameter, the device achieves improved external quantum efficiency while maintaining manageable structural complexity through a clear material selection criterion.
3Loss of energy
If blue-emission fluorescent device is optimized for efficiency, then the external quantum efficiency reaches about 8%, but the voltage required is still 4 to 6 V
Solution Approach 1:
The blocking layer serves as an intermediary that facilitates efficient electron-hole recombination by confining triplet excitons and promoting their collision with electrons. This mediation enables the device to achieve higher external quantum efficiency without requiring excessive voltage, as the TTF phenomenon occurs more readily at lower voltages due to the blocking layer's triplet energy confinement effect.
Solution Approach 2:
By changing the triplet energy parameter of the blocking layer to be higher than the host material, the device enables more efficient triplet exciton utilization. This parameter change allows the recombination process to occur more efficiently at lower voltages, thereby resolving the contradiction between achieving high efficiency and maintaining reasonable operating voltage.
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 use of an aromatic heterocyclic derivative with an azine ring in the blocking layer significantly improves the external quantum efficiency of the organic electroluminescence device, allowing for a high-efficiency fluorescent emission by efficiently utilizing triplet excitons through the TTF phenomenon, achieving a luminous intensity from single excitons generated by triplet exciton collisions that accounts for 30% or more of the total luminous intensity.
Implementation Method 1
A mechanism is found that singlet excitons are generated by collision and fusion of two triplet excitons, whereby fluorescent emission is increased. Such a phenomenon in which singlet excitons are generated by collision and fusion of two triplet excitons is hereinafter referred to as TTF (Triplet-Triplet Fusion) phenomenon.
Implementation Method 2
When a voltage is applied to the organic EL device, holes are injected from an anode and electrons are injected from a cathode. The holes and the electrons are recombined in an emitting layer to form excitons.
Data Source
AI summary
An organic electroluminescence device that includes an anode, an emitting layer that includes a host and a fluorescent dopant, an electron transporting zone, a cathode, a blocking layer adjacent to the emitting layer in the electron transporting zone where the blocking layer includes an aromatic heterocyclic derivative with an azine ring and where the triplet energy ETb (eV) of the aromatic heterocyclic derivative is larger than a triplet energy ETh (eV) of the host.