Organic EL Device Blocking Layer Triplet Energy
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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 TTF phenomenon is hindered by affinity differences between layers, leading to reduced exciton generation and luminous efficiency.
Innovation Solution
An organic electroluminescence device structure is implemented with a blocking layer and electron injecting layer having a predetermined affinity difference, utilizing an aromatic heterocyclic derivative with a higher triplet energy than the host, and a dopant with a triplet energy larger than the host, to facilitate the TTF phenomenon and enhance luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a blocking layer with large affinity difference from the electron injecting layer is used, then electron supply to the emitting layer is insufficient, but exciton generation is improved
Solution Approach 1:
The patent changes the affinity parameter relationship between blocking layer and electron injecting layer by specifying that their affinity difference should be less than 0.2 eV. This parameter optimization allows sufficient electron supply to the emitting layer while maintaining conditions favorable for TTF phenomenon and triplet exciton utilization.
2Loss of energy
If conventional electron transporting materials are used in the blocking layer, then TTF phenomenon cannot occur, but device structure is simpler
Solution Approach 1:
The patent changes the material selection criterion for the blocking layer by specifying triplet energy parameter requirements (ETb > ETh) and affinity relationship (Ae - Ab < 0.2 eV). These parameter specifications enable TTF phenomenon occurrence in the blocking layer while maintaining a relatively simple layered structure.
Solution Approach 2:
The blocking layer acts as an intermediary between the emitting layer and electron injecting layer, with specifically controlled affinity and triplet energy parameters. This intermediary layer facilitates electron transport while enabling TTF phenomenon, bridging the functional requirements of both adjacent layers.
3Productivity
If triplet energy of blocking layer material is not higher than host, then TTF phenomenon is suppressed, but manufacturing is easier
Solution Approach 1:
The patent establishes a clear parameter criterion that the triplet energy of the blocking layer material (ETb) must be higher than that of the host material (ETh). This parameter specification enables TTF phenomenon and high luminous efficiency while providing a straightforward material selection guideline for manufacturing.
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 structure effectively increases the density of triplet excitons within the emitting layer, leading to improved luminous efficiency and efficient generation of singlet excitons through the TTF phenomenon, thereby enhancing the overall efficiency of the fluorescent emission.
Implementation Method 1
When a voltage is applied to the organic EL device, holes are injected from an anode and electrons are injected from a cathode
Implementation Method 2
The holes and the electrons are recombined in an emitting layer to form excitons. According to the electron spin statistics theory, singlet excitons and triplet excitons are generated at a ratio of 25%:75%
Implementation Method 3
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 4
the blocking layer includes an aromatic heterocyclic derivative, a triplet energy ETb (eV) of the aromatic heterocyclic derivative is larger than a triplet energy ETh (eV) of the host
Implementation Method 5
In a fluorescent EL device which uses emission caused by singlet excitons
Data Source
AI summary
An organic electroluminescence device that includes an anode, an emitting layer that includes a host and a dopant, a blocking layer, an electron injecting layer, and a cathode where the blocking layer includes an aromatic heterocyclic derivative, the triplet energy ETb (eV) of the blocking layer is larger than a triplet energy ETh (eV) of the host, and the affinity Ab (eV) of the blocking layer and an affinity Ae (eV) of the electron injecting layer satisfy a relationship of Ae−Ab<0.2.