Organic Electroluminescent Element Emitter Layer Composition
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Solution Overview
Problem
Current organic electroluminescence devices with thermally activated delayed fluorescence (TADF) mechanisms require improvement in performance to enhance efficiency and longevity.
Innovation Solution
An organic electroluminescence device comprising an anode, an emitting layer with a first delayed fluorescent compound, a second fluorescent compound, and a third compound with high electron mobility, where the ionization potentials of the compounds satisfy specific relationships to prevent simultaneous trapping of holes and electrons, thereby improving electron transport and reducing luminous efficiency roll-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a TADF mechanism is used in an organic EL device, then the internal quantum efficiency can be improved beyond 25%, but the device performance requires further improvement in terms of stability and longevity
Solution Approach 1:
The patent employs a composite emitting layer containing three distinct compounds: a delayed fluorescent compound (first compound), a fluorescent compound (second compound), and an electron transporting compound (third compound). This composite material system leverages the TADF mechanism of the first compound to achieve high internal quantum efficiency while the second and third compounds provide structural stability and improved device longevity, respectively.
Solution Approach 2:
The patent optimizes specific physical parameters of the compounds in the emitting layer. The ionization potential difference between the first and second compounds is controlled to be 0≤Ip2−Ip1≤0.8 eV, and the electron mobility of the third compound is maintained at 1×10−8 cm2/(V·s) or more. These parameter optimizations enable efficient exciton management and charge transport, improving both efficiency and device stability.
2Productivity
If triplet excitons are utilized in combination with singlet excitons, then light emission efficiency can be enhanced, but simultaneous trapping of holes and electrons occurs reducing overall efficiency
Solution Approach 1:
The patent assigns specific functional roles to different compounds in the emitting layer based on their local properties. The first compound (delayed fluorescent) is positioned to generate triplet excitons and facilitate RISC, while the second compound (fluorescent) is selected with specific ionization potential to accept excitons without simultaneous charge trapping. The third compound provides electron transport capability. This functional differentiation based on local material properties prevents simultaneous trapping while maintaining high emission efficiency.
Solution Approach 2:
The second fluorescent compound acts as an intermediary between the delayed fluorescent compound and the electron transporting compound. It receives excitons from the first compound through energy transfer and transfers them to the third compound, preventing direct interaction between charge carriers that would lead to simultaneous trapping. The controlled ionization potential difference ensures this intermediary function operates efficiently.
3Speed
If the ionization potential difference between compounds is optimized, then electron transport is improved, but the device complexity increases due to multiple compound requirements
Solution Approach 1:
The patent implements a moderate level of complexity by using exactly three compounds in the emitting layer - no fewer to maintain necessary functions, no more to avoid excessive complexity. Each compound performs a specific partial function: the first compound handles TADF and triplet exciton management, the second compound manages energy transfer and prevents charge trapping, and the third compound provides electron transport. This partial specialization achieves efficient electron transport without overwhelming system complexity.
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 solution achieves high internal quantum efficiency and extended device lifetime by optimizing the energy levels and mobilities of the compounds in the emitting layer, inhibiting exciton deactivation and enhancing luminous efficiency.
Implementation Method 1
a phenomenon where reversed inter-system crossing (RISC) from triplet excitons to singlet excitons thermally occurs when a material having a small energy difference (ΔST) between singlet energy level and triplet energy level is used
Implementation Method 2
a thermally activated delayed fluorescence (TADF) mechanism has been studied
Implementation Method 3
The injected electrons and holes are recombined in the emitting layer to form excitons
Implementation Method 4
When a voltage is applied to an organic electroluminescence device, holes and electrons are injected from an anode and a cathode into an emitting layer
Data Source
AI summary
An organic electroluminescence device includes an anode, an emitting layer, and a cathode. The emitting layer contains a first compound, a second compound, and a third compound. An ionization potential Ip1 of the first compound and an ionization potential Ip2 of the second compound satisfy the numerical expression.0≤Ip2−Ip1≤0.8[eV]The first compound is a delayed fluorescent compound. The second compound is a fluorescent compound. The third compound has an electron mobility of 1×10−8 cm2/(V·s) or more.