Coating Liquid for Organic EL Light Emitting Layer
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Solution Overview
Problem
Current organic electroluminescent elements, particularly those emitting blue light, face challenges in achieving high quantum efficiency and long service life due to the requirement for a wide energy gap between the ground and excited states, which compromises molecular stability and luminescent efficiency.
Innovation Solution
A coating solution comprising a thermally-activated delayed fluorescent compound and a phosphorescent metal complex is used to form a luminous layer, where the energy levels of the compounds allow for efficient intersystem crossing, enhancing quantum efficiency and preventing agglomeration, thereby improving the service life and luminescent efficiency of organic electroluminescent elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a wide energy gap between ground state and excited state is used to achieve blue light emission, then light emission wavelength is shortened (bluer color), but molecular stability is reduced and service life is shortened
Solution Approach 1:
The patent introduces a host compound as an intermediary substance that accommodates the blue fluorescent material. The host compound has a triplet energy level higher than the blue fluorescent material, enabling efficient energy transfer while the host matrix provides structural stability and prevents direct degradation of the luminous material, thus extending service life while maintaining blue emission
Solution Approach 2:
The patent optimizes multiple parameters including the energy gap between singlet and triplet states (ΔEST), the triplet energy level of the host compound, and the concentration of fluorescent material. By carefully controlling these parameters, the invention achieves blue light emission with improved molecular stability and extended service life
2Use of energy by moving object
If phosphorescent materials are used to utilize both singlet and triplet excitons, then luminescent efficiency is improved, but triplet energy level requirements for blue emission reduce molecular stability
Solution Approach 1:
The host compound serves as an intermediary that receives energy from both singlet and triplet excitons generated by the blue fluorescent material. The host's higher triplet energy level allows it to accept triplet excitons without energy loss, then transfer this energy back to the fluorescent material for light emission, achieving high luminescent efficiency while the host matrix protects the luminous material from degradation
Solution Approach 2:
The patent creates a composite luminous layer combining blue fluorescent material with a host compound having specific energy level characteristics. This composite structure enables the system to utilize both singlet and triplet excitons through the fluorescent material-host interaction, achieving phosphorescent-like efficiency with fluorescent materials while maintaining molecular stability through the protective host matrix
3Power
If triplet-triplet fusion phenomenon is enhanced in fluorescent materials, then power efficiency is doubled or tripled, but fundamental 50% conversion limit from triplet to singlet state remains
Solution Approach 1:
The host compound acts as an intermediary energy reservoir that facilitates triplet-triplet fusion. Triplet excitons are transferred to the host, where they can undergo fusion processes, and the resulting singlet excitons are transferred back to the fluorescent material for light emission. This intermediary mechanism bypasses the direct 50% conversion limit by using the host's higher energy level as a platform for more efficient energy conversion
Solution Approach 2:
The patent optimizes the energy level difference between the host compound and the fluorescent material, specifically controlling the triplet energy level of the host to be higher than that of the fluorescent material. This parameter optimization enables enhanced triplet-triplet fusion while exceeding the traditional 50% conversion limit through the host-mediated energy transfer process
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 the quantum efficiency and service life of organic electroluminescent elements by promoting intersystem crossing and reducing agglomeration, leading to improved luminescent performance and reliability.
Implementation Method 1
the energy levels of the compounds allow for efficient intersystem crossing, enhancing quantum efficiency
Implementation Method 2
a heavy atom compound having an external heavy-atom effect to promote intersystem crossing of the thermally-activated delayed fluorescent compound from a triplet excited state to a singlet excited state to increase a fluorescent intensity
Implementation Method 3
the concentration of the fluorescent compound and the type of solvent can prevent the fluorescent compound from agglomerating
Data Source
AI summary
One objective of the present invention is to provide a coating liquid for forming a light emitting layer, which improves quantum efficiency. Another objective of the present invention is to provide: an organic electroluminescent element which is formed by means of this coating liquid for forming a light emitting layer; a lighting device, a display device and a white electroluminescent device, each of which is provided with this organic electroluminescent element; and a method for manufacturing an organic electroluminescent element. A coating liquid for forming a light emitting layer according to the present invention is used for the purpose of forming a light emitting layer, which is one of one or more organic layers held between a positive electrode and a negative electrode, and this coating liquid for forming a light emitting layer is characterized by containing a thermally activated delayed fluorescent compound.