Organic EL Device Mixed Host Material Triplet-Triplet Fusion
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Solution Overview
Problem
Current organic electroluminescent (EL) devices face limitations in luminous efficiency and stability, particularly requiring improvements in internal quantum efficiency and driving voltage characteristics for practical application in display devices.
Innovation Solution
An organic EL device is developed using a specific mixed host material in the light-emitting layer, comprising compounds represented by general formulas (1) and (2), with a dopant, to enhance charge transport properties and localization of light emission, thereby improving efficiency and durability at low voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluorescence-emitting organic EL device using light emission from singlet excitons is used, then the device structure is simple, but the internal quantum efficiency is limited to 25%
Solution Approach 1:
The patent employs a composite host system consisting of a first host material and a second host material with different triplet energy levels. This composite structure enables simultaneous achievement of simple device architecture and high internal quantum efficiency through the TTF mechanism, resolving the contradiction between structural simplicity and energy utilization efficiency.
Solution Approach 2:
The patent optimizes specific parameters including the triplet energy level difference between host materials (Et2 - Et1 = 0.5-2.0 eV), dopant concentration (0.1-10 wt%), and host material ratios to maximize the TTF mechanism efficiency. These parameter adjustments enable the system to achieve over 25% internal quantum efficiency while maintaining structural simplicity.
2Use of energy by moving object
If a phosphorescent organic EL device using light emission from triplet excitons is used, then the internal quantum efficiency is enhanced to 100%, but the device complexity increases
Solution Approach 1:
The patent replaces expensive phosphorescent dopants and complex device structures with a simpler TTF-based fluorescent system. The short-lived triplet excitons in the first host material are converted to singlet excitons through collision with the second host material, achieving high efficiency without requiring phosphorescent materials or complex device architectures.
3Use of energy by moving object
If delayed fluorescence mechanisms (TTF or TADF) are used to improve internal quantum efficiency, then efficiency can be raised to 40% or 100%, but the device life and stability remain insufficient
Solution Approach 1:
The patent creates distinct functional zones within the light-emitting layer by using two host materials with different triplet energy levels. The first host material (higher Et) localizes triplet excitons and prevents their migration to the second host material, while the second host material (lower Et) provides the TTF mechanism. This spatial separation of functions enhances both efficiency and device stability.
Solution Approach 2:
The second host material acts as an intermediary that facilitates the TTF mechanism without permanently trapping excitons. It enables efficient singlet exciton generation through triplet-triplet fusion while its lower triplet energy level prevents exciton leakage, thereby improving both efficiency and device lifetime.
4Ease of manufacture
If conventional host materials are used in the light-emitting layer, then the device can be manufactured with standard processes, but the luminous efficiency and driving voltage characteristics are insufficient
Solution Approach 1:
The patent designs host materials that simultaneously perform multiple functions: charge transport, exciton confinement, and TTF mechanism facilitation. The first host material transports charges and confines triplet excitons, while the second host material enables the TTF mechanism. This multi-functionality allows standard manufacturing processes to produce devices with superior luminous efficiency and driving voltage characteristics.
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 results in an organic EL device with enhanced luminous efficiency, extended life, and reduced driving voltage, achieving high efficiency and stability by controlling charge injection and localization within the light-emitting layer.
Implementation Method 1
The TTF mechanism utilizes a phenomenon in which singlet excitons are generated due to collision of two triplet excitons
Implementation Method 2
The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing from triplet excitons to singlet excitons is generated in a material having a small energy difference between a singlet level and a triplet level
Implementation Method 3
Application of a voltage to an organic EL device allows injection of holes and electrons from an anode and a cathode, respectively, into a light-emitting layer
Implementation Method 4
the light-emitting layer comprises a compound represented by the general formula (1), a compound represented by the general formula (2) and a dopant
Data Source
AI summary
To provide an organic electroluminescent device realizing high efficiency and low voltage characteristics. A light-emitting layer including compounds of (1) and (2) and a dopant is included. X represents N or CR3, wherein at least one X represents N. R1 represents (1b), R2 represents (1c), and R3 represents an alkyl group or the like. Y represents O, S, NR4, or CR5R6, R4 to R6 each represent an alkyl group or the like, and one of R7 to R14 binds to a ring in (1). * represents a binding position to a ring in (1), and rings C and D are each an aromatic ring fused to an adjacent ring. R15, R16 and R17 have the same meaning as R3 (a and b represent the number of substitutions). R19 has the same meaning as R4, and R20 to R27 each represent CR3, CR28 or N and at least one thereof represents CR28, and R28 represents formula (2b). Z represents O, S, NR37, or CR38R39, R37 to R39 each has the same meaning as R4, and one of R29 to R36 binds to a ring in (2) and the others represent CR3 or N.