Organic EL Host Composition for Low-Voltage Stable Emission
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Solution Overview
Problem
Existing organic electroluminescent (EL) devices face challenges in achieving high luminous efficiency, low drive voltage, and long lifespan, particularly in phosphorescent and delayed fluorescence mechanisms.
Innovation Solution
The use of a specific indolocarbazole compound as a first host, combined with a second host selected from compounds represented by General Formulae (2) or (3), in the light emitting layer of an organic EL device, along with a luminescent dopant, to enhance charge injection and transport capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent organic EL device is used to increase internal quantum efficiency to up to 100%, then luminous efficiency is improved, but device lifespan becomes insufficient
Solution Approach 1:
The patent changes the chemical structure parameters of the host material by introducing specific indolocarbazole compounds with particular substituents (Formula 1) and combining them with carbazole or dibenzofuran compounds (Formulae 2 and 3). This structural parameter change enables the material to achieve both high triplet energy levels (improving efficiency) and enhanced stability (improving lifespan), resolving the contradiction between efficiency and durability.
Solution Approach 2:
The patent creates a composite host material system by combining indolocarbazole compounds (Formula 1) with carbazole or dibenzofuran compounds (Formulae 2 and 3) in specific weight ratios (70:30 to 30:70). This composite approach leverages the high triplet energy of indolocarbazole for efficiency while the carbazole/dibenzofuran components contribute to stability and lifespan, simultaneously addressing both contradictory requirements.
2Use of energy by moving object
If a thermally activated delayed fluorescence (TADF) mechanism is used to increase internal quantum efficiency to 100%, then luminous efficiency is improved, but device lifespan remains insufficient
Solution Approach 1:
The patent modifies the energy level parameters and molecular structure of the host material using indolocarbazole compounds with specific substituents (Formula 1) combined with carbazole or dibenzofuran compounds. This parameter optimization enables efficient reverse intersystem crossing for TADF while the robust molecular structure and high triplet energy levels simultaneously enhance device lifespan, resolving the efficiency-lifespan contradiction.
Solution Approach 2:
The patent employs a composite material system combining indolocarbazole compounds (Formula 1) with carbazole or dibenzofuran compounds (Formulae 2 and 3) in optimized ratios. The indolocarbazole component facilitates TADF through small singlet-triplet energy gaps while the carbazole/dibenzofuran components provide structural stability and extended lifespan, achieving both high efficiency and durability.
3Use of energy by moving object
If triplet-triplet fusion (TTF) mechanism is used to achieve delayed fluorescence, then internal quantum efficiency increases to 40%, but efficiency remains lower than phosphorescent devices
Solution Approach 1:
The patent optimizes the triplet energy level parameters and molecular structure of the host material by using indolocarbazole compounds (Formula 1) combined with carbazole or dibenzofuran compounds (Formulae 2 and 3). This parameter optimization enhances the TTF mechanism efficiency by improving triplet exciton population and collision probability, enabling the system to surpass conventional TTF-based devices and approach phosphorescent device efficiency levels.
Solution Approach 2:
The patent creates a composite host system combining indolocarbazole compounds (Formula 1) with carbazole or dibenzofuran compounds (Formulae 2 and 3) in specific ratios. This composite structure enhances triplet energy levels and improves triplet exciton dynamics, thereby boosting TTF mechanism efficiency and achieving luminous efficiency comparable to or exceeding conventional phosphorescent devices.
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 configuration results in an organic EL device with improved power efficiency, extended lifespan, and high drive stability, effectively addressing the limitations of previous technologies.
Implementation Method 1
The use of a specific indolocarbazole compound as a first host, combined with a second host selected from compounds represented by General Formulae (2) or (3), in the light emitting layer of an organic EL device, along with a luminescent dopant, to enhance charge injection and transport capabilities
Implementation Method 2
When a voltage is applied to an organic EL device, holes from an anode and electrons from a cathode are injected into a light emitting layer. Then, the injected holes and electrons are recombined in the light emitting layer to generate excitons
Implementation Method 3
it is known that the internal quantum efficiency of a phosphorescent organic EL device in which light emission due to triple excitons is used can increase to up to 100% in a case where intersystem crossing from singlet excitons is efficiently performed
Implementation Method 4
In the TADF mechanism, a phenomenon that reverse intersystem crossing from triple excitons to singlet exciton is caused in materials having a small energy difference between a singlet level and a triple level is used, and therefore, it is theoretically thought that the internal quantum efficiency can be increased to 100%
Data Source
AI summary
Provided is an organic EL device including: a light emitting layer between an anode and a cathode facing each other, in which the light emitting layer contains a first host, a second host, and a luminescent dopant, an indolocarbazole compound represented by General Formula (1) is contained as the first host, and a biscarbazole compound or a dibenzofuran compound having a dibenzofuran or dibenzothiophene ring is contained as the second host. This organic EL device has a low drive voltage, high efficiency, and high drive stability.