Exciplex Light-Emitting Element for Efficient Triplet Conversion
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Solution Overview
Problem
Existing light-emitting elements using thermally activated delayed fluorescent materials face challenges in efficiently generating singlet excited states from triplet excited states, leading to suboptimal luminous efficiency, high driving voltage, and high power consumption.
Innovation Solution
A light-emitting element is designed with a light-emitting layer containing two organic compounds that form an exciplex, where one compound converts triplet excitation energy into light emission, and the energy levels are aligned to facilitate efficient formation of an exciplex with a small energy difference between singlet and triplet excited states, promoting reverse intersystem crossing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a thermally activated delayed fluorescent material is used in a light-emitting element, then the element can convert triplet excitation energy into light emission, but the luminous efficiency remains suboptimal due to inefficient generation of singlet excited states from triplet excited states
Solution Approach 1:
The patent introduces an exciplex system as an intermediary mechanism between triplet and singlet states. The exciplex forms between a donor compound and acceptor compound, creating a complex that facilitates reverse intersystem crossing from triplet to singlet excited states through its unique energy level structure, thereby improving the efficiency of singlet state generation from triplet states
Solution Approach 2:
The patent optimizes the energy level parameters of the exciplex system by carefully selecting donor and acceptor compounds with specific HOMO and LUMO levels. The energy difference between singlet and triplet states in the exciplex is controlled to be small, enabling efficient thermal activation and reverse intersystem crossing, thus improving luminous efficiency
2Loss of energy
If conventional thermally activated delayed fluorescent materials are used, then triplet excitation energy can be partially converted into light emission, but the driving voltage remains high
Solution Approach 1:
The patent divides the light-emitting layer into distinct functional components: a donor compound and an acceptor compound that form the exciplex. This segmentation allows each component to be optimized for its specific function - the donor for generating excitons and the acceptor for facilitating reverse intersystem crossing - resulting in lower driving voltage while maintaining efficient triplet energy utilization
3Illumination intensity
If traditional fluorescent or phosphorescent compounds are used, then light emission can be achieved, but power consumption remains high due to incomplete utilization of excitons
Solution Approach 1:
The patent employs a composite material system consisting of a donor compound and an acceptor compound that form an exciplex. This composite structure combines the advantages of both components: the donor provides efficient exciton generation and the acceptor enables effective reverse intersystem crossing, achieving near 100% utilization of both singlet and triplet excitons for light emission, thereby significantly reducing power consumption
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 enhances luminous efficiency, reduces driving voltage, and lowers power consumption while providing a highly reliable light-emitting element with improved luminous efficiency and stability.
Implementation Method 1
Light emission from the triplet excited state is referred to as phosphorescence. The formation ratio of S* to T* in a light-emitting element is 1:3. Thus, a light-emitting element containing a compound that emits phosphorescence (phosphorescent compound) has higher luminous efficiency
Implementation Method 2
In a thermally activated delayed fluorescent material, a singlet excited state is generated from a triplet excited state by reverse intersystem crossing, and the singlet excited state is converted into light emission
Implementation Method 3
Patent Document 1, for example, discloses a method in which an exciplex formed by two kinds of organic compounds is used as a thermally activated delayed fluorescent material because the energy difference between a singlet excited state and a triplet excited state is small
Implementation Method 4
voltage application between the pair of electrodes causes injection of electrons from a cathode and holes from an anode into the EL layer having a light-emitting property; thus, current flows
Implementation Method 5
By recombination of the injected electrons and holes, the light-emitting organic compound is brought into an excited state to provide emission
Data Source
AI summary
A light-emitting element with high luminous efficiency is provided. The light-emitting element contains a first organic compound and a second organic compound. The first and second organic compounds form an exciplex. The first organic compound emits no fluorescence but phosphorescence at a temperature ranging from low temperature to normal temperature. The luminescence quantum yield of the first organic compound is higher than or equal to 0% and lower than or equal to 40% at room temperature. Light emitted from the light-emitting element includes light emitted from an exciplex formed by the first organic compound and the second organic compound.