Fluorescent Light-Emitting Layer Using TADF Triplet Conversion
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Solution Overview
Problem
Fluorescent light-emitting elements have lower emission efficiency and require higher current and heat generation due to inefficient conversion of triplet excitation energy, making them less reliable and requiring higher driving voltages.
Innovation Solution
A light-emitting element structure incorporating a light-emitting layer with specific organic compounds, including a first compound that converts triplet excitation energy into light emission, a second compound with a π-electron rich and π-electron deficient skeleton for improved carrier transport, and a third compound that converts singlet excitation energy into light emission, optimizing energy transfer and reducing driving voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fluorescent compound is used as the light-emitting substance, then stability is improved, but emission efficiency deteriorates due to inefficient conversion of triplet excitation energy
Solution Approach 1:
The patent uses a composite light-emitting layer containing both a fluorescent compound and a thermally activated delayed fluorescent (TADF) compound. The TADF compound converts triplet excitation energy into singlet excitation energy through reverse intersystem crossing, while the fluorescent compound emits light from singlet excited states. This composite approach maintains the stability of fluorescent materials while improving emission efficiency through the energy conversion capability of TADF materials.
Solution Approach 2:
The patent modifies the energy level parameters of the light-emitting substances by selecting specific TADF compounds with particular singlet-triplet energy differences. By controlling the energy levels of the TADF compound relative to the fluorescent compound, the system achieves efficient energy transfer from triplet to singlet states, thereby improving emission efficiency while maintaining stability.
2Reliability
If a fluorescent light-emitting element is used, then reliability is improved through stable compounds, but driving voltage increases due to higher current requirements
Solution Approach 1:
The composite light-emitting layer combines a fluorescent compound with a TADF compound that has superior carrier transport properties. The TADF compound facilitates more efficient charge carrier injection and transport, reducing the current density required for operation. This lowers the driving voltage while maintaining the reliability benefits of using stable fluorescent materials.
Solution Approach 2:
The TADF compound acts as an intermediary that converts triplet excitation energy into singlet excitation energy, which then transfers energy to the fluorescent compound for light emission. This energy conversion mechanism reduces the need for high current densities, thereby lowering driving voltage while preserving the reliability of the fluorescent material system.
3Loss of energy
If triplet excitation energy is not efficiently converted, then emission efficiency is low, but heat generation increases
Solution Approach 1:
The patent utilizes TADF compounds with specific energy level parameters where the singlet-triplet energy difference is small but positive. This parameter configuration enables efficient reverse intersystem crossing from triplet to singlet states, converting non-emissive triplet energy into emissive singlet energy. This energy conversion pathway reduces heat generation from non-radiative decay while improving overall emission efficiency.
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 emission efficiency, reduces driving voltage, and increases reliability of fluorescent light-emitting elements by efficiently converting triplet excitation energy into singlet excitation energy, leading to high color purity and lower power consumption.
Implementation Method 1
a first organic compound having a function of converting triplet excitation energy into light emission
Implementation Method 2
a third organic compound having a function of converting singlet excitation energy into light emission
Implementation Method 3
by voltage application between the pair of electrodes, electrons from a cathode and holes from an anode are injected into the EL layer having a light-emitting property; thus, current flows
Data Source
AI summary
A light-emitting element having high emission efficiency is provided.The light-emitting element includes a first organic compound, a second organic compound, and a third organic compound. The first organic compound has a function of converting triplet excitation energy into light emission. The second organic compound is preferably a TADF material. The third organic compound is a fluorescent compound. Light emitted from the light-emitting element is obtained from the third organic compound. Triplet excitation energy in a light-emitting layer is transferred to the third organic compound by reverse intersystem crossing caused by the second organic compound or through the first organic compound.