Exciplex Light-Emitting Element for Low-Voltage High-Efficiency EL
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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 LUMO and HOMO levels of these compounds are strategically aligned to facilitate efficient formation of an exciplex, promoting reverse intersystem crossing and reducing driving voltage.
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 excited states. The exciplex forms between a phosphorescent compound (compound 1) and a fluorescent compound (compound 2), creating a coupled system where energy transfer occurs through the exciplex state. This intermediary exciplex mechanism enables efficient reverse intersystem crossing from triplet to singlet states, resolving the contradiction by providing a pathway that is more efficient than direct conversion while maintaining the ability to utilize triplet excitation energy.
Solution Approach 2:
The patent employs a composite material system consisting of two distinct organic compounds (a phosphorescent compound containing heavy atoms and a fluorescent compound) that work together to form the exciplex. This composite approach combines the advantages of both phosphorescent materials (efficient triplet state utilization) and fluorescent materials (high radiative decay rate from singlet states), achieving superior luminous efficiency compared to using either compound alone.
2Device complexity
If conventional organic EL materials are used, then the device structure is simple, but the driving voltage remains high and power consumption is high
Solution Approach 1:
The patent optimizes the energy level parameters of the exciplex system by carefully selecting compounds with appropriate HOMO and LUMO levels. The energy difference between the exciplex singlet and triplet states is controlled to be small (less than 0.2 eV), which facilitates efficient reverse intersystem crossing. Additionally, the highest occupied molecular orbital (HOMO) level of the exciplex is optimized to be lower than that of conventional materials, which directly reduces the driving voltage required for carrier injection and transport, thereby reducing power consumption while maintaining the relatively simple organic EL device structure.
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 performance.
Implementation Method 1
light emission from the triplet excited state is referred to as phosphorescence
Implementation Method 2
a singlet excited state is generated from a triplet excited state by reverse intersystem crossing
Implementation Method 3
research and development of light-emitting elements using electroluminescence (EL)
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.