Exciplex-Excimer Host System for OLED Efficiency and Stability
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Solution Overview
Problem
Traditional organic electroluminescent devices face issues such as low efficiency, poor stability, and color purity due to imbalanced carrier transport, excessive triplet exciton concentration, and inefficient energy transfer, particularly with thermally activated delayed fluorescence (TADF) materials, which struggle to simultaneously achieve high exciton utilization and fluorescent radiation efficiency.
Innovation Solution
The use of an organic electroluminescent device structure comprising a luminescent layer with a host material formed by a mixture of first, second, and third organic compounds, where the exciplex and excimer are generated to balance carriers, reduce triplet exciton concentration, and enhance energy transfer, utilizing the triplet excitons of the host material to convert into singlet excitons for improved luminescent efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional host and guest materials are used in a doping system, then energy transfer efficiency can be improved, but carrier mobility imbalance causes exciton recombination region deviation and reduces device efficiency and stability
Solution Approach 1:
The patent employs a composite host material system comprising three distinct organic compounds (first host compound, second host compound, and third host compound) with different carrier mobility characteristics. This composite approach allows simultaneous optimization of energy transfer efficiency and carrier balance, resolving the contradiction between energy transfer performance and device stability. The first and second host compounds form an exciplex system for efficient energy transfer, while the third host compound provides balanced carrier transport.
2Productivity
If phosphorescent material is used to utilize both singlet and triplet excitons, then internal quantum efficiency can reach 100%, but the material suffers from expensive price, poor stability, and serious device efficiency drop
Solution Approach 1:
The patent changes the fundamental parameters of the luminescent system by using TADF materials with specific singlet-triplet energy level differences (ΔEST) and implementing an exciplex-host system. This allows the device to achieve high internal quantum efficiency through triplet exciton upconversion without relying on phosphorescent materials containing heavy metals, thereby improving both efficiency and material stability simultaneously.
3Productivity
If TADF material with small singlet-triplet energy level difference is used to convert triplet excitons into singlet excitons, then internal quantum efficiency can reach 100%, but fluorescent radiation efficiency decreases
Solution Approach 1:
The patent introduces an exciplex system formed by the first and second host compounds as an intermediary energy transfer mediator. The exciplex receives energy from the third host compound and transfers it to the guest material, providing an additional energy transfer pathway that maintains high internal quantum efficiency while preserving fluorescent radiation efficiency through the exciplex's radiative decay.
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
This approach effectively improves the efficiency and lifetime of organic light-emitting devices by balancing carriers, reducing triplet exciton quenching, and promoting thermal and chemical stability, while ensuring efficient energy transfer to the guest material, thereby enhancing the overall performance and longevity of the device.
Implementation Method 1
the first organic compound and the second organic compound form a mixture or a laminated interface which generates an exciplex under the condition of optical excitation or electric field excitation
Implementation Method 2
utilizing the triplet excitons of the host material to convert into singlet excitons for improved luminescent efficiency and stability
Implementation Method 3
when a voltage is applied between electrodes sandwiched with the luminescent layer, electrons injected from the anode and holes injected from the cathode are recombined in the luminescent layer to form excitons, and the excitons are relaxed to a ground state to release energy to form photons
Implementation Method 4
the third organic compound is doped into the mixture or laminated interface formed by the first and second organic compounds and forms an intramolecular excimer
Implementation Method 5
The thermally activated delayed fluorescence (TADF) material is a third-generation organic luminescent material developed after the organic fluorescent material and the organic phosphorescent material
Data Source
AI summary
The present invention relates to an exciplex and excimer system-based organic electroluminescent device. The host material of the light emitting layer comprises first, second and third organic compounds. A mixture or lamination formed by the first and second organics produces an exciplex under light or electrical excitation. The third organic compound is doped in the mixture or a layer of the lamination formed by the first and second organic compounds, and the third organic compound forms an excimer. The singlet energy level of the exciplex is higher than the singlet energy level of the third organic compound, and the triplet energy level thereof is higher than the triplet energy level of the third organic compound. The device of the present invention has the characteristics of high efficiency and long service time.