Benzoazole Hole Blocking Layer for Organic EL Efficiency
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Solution Overview
Problem
Current organic electroluminescence (EL) devices face challenges in achieving high light emission efficiency, low driving voltage, long lifetime, and durability due to inadequate electron injection/transport and hole blocking properties in existing materials, particularly with compounds like Alq3 and TAZ, which have slow electron movement and poor film stability.
Innovation Solution
A two-layer structure is implemented with a benzoazole-based material as a hole blocking layer and specific arylamine or pyrimidine compounds as hole and electron transport layers to enhance carrier balance and exciton confinement, improving electron injection, hole blocking, and film stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Alq3 is used as electron transport material, then electron transport function is provided, but electron movement is slow and hole blocking property is insufficient
Solution Approach 1:
The electron transport layer is divided into two separate functional layers: a first electron transport layer (ETL1) using Alq3 for electron transport, and a second electron transport layer (ETL2) using TAZ for hole blocking. This segmentation allows each layer to specialize in its primary function without compromise.
Solution Approach 2:
Different regions of the electron transport layer are assigned different material properties: the region adjacent to the light-emitting layer uses TAZ with high hole blocking capability (work function 6.6 eV), while the region adjacent to the electron injection layer uses Alq3 with good electron transport capability. This local differentiation optimizes both functions simultaneously.
2Reliability
If TAZ is used to improve hole blocking property, then hole blocking performance is enhanced, but electron transport property becomes insufficient
Solution Approach 1:
The electron transport layer is segmented into two layers with TAZ-based ETL2 positioned to perform hole blocking function while Alq3-based ETL1 handles electron transport, allowing TAZ to fulfill its hole blocking role without compromising overall electron transport.
Solution Approach 2:
The Alq3-based first electron transport layer acts as an intermediary between the cathode and the TAZ-based second electron transport layer, facilitating electron transport to the interface where hole blocking occurs, thus mediating between electron injection and hole blocking functions.
3Ease of manufacture
If materials with low heat resistance are used, then device manufacturing is easier, but thermal decomposition occurs at low temperature due to heat generated during device operation
Solution Approach 1:
The patent selects materials with specific thermal parameters: Alq3 with glass transition temperature of 83°C and TAZ with glass transition temperature of 120°C. These parameter selections ensure the materials can withstand operational temperatures without decomposition while maintaining ease of deposition from organic solvent solutions.
4Ease of manufacture
If materials with low amorphous property are used, then material deposition is simpler, but crystallization of thin film occurs quickly leading to device degradation
Solution Approach 1:
The patent utilizes materials with specific glass transition temperatures (Alq3: 83°C, TAZ: 120°C) that allow formation of stable amorphous thin films at device operating temperatures. The materials are deposited from organic solvent solutions, and their thermal parameters ensure they remain amorphous and stable during device operation.
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 organic EL devices with improved light emission efficiency, reduced driving voltage, extended lifetime, and enhanced durability by effectively controlling hole movement and exciton confinement.
Implementation Method 1
a compound having a benzoazole structure represented by general formula (1) ... as a material for a hole blocking layer
Implementation Method 2
charges injected from both electrodes are recombined in the light-emitting layer to obtain light emission
Implementation Method 3
an electron transport material having a high electron injection property, a high mobility of electrons
Implementation Method 4
a device using light emission by thermally activated delayed fluorescence (TADF)
Data Source
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AI summary
[Object] It is an object of the present invention to provide an organic EL device in which, as a highly efficient and highly durable organic EL material, various materials excelling in electron injection/transport performance, hole blocking performance, hole resistance performance, exciton confinement performance, stability in a film state, and durability, are combined so that properties of each material can be effectively demonstrated, thereby achieving (1) high light emission efficiency and power efficiency, (2) low luminescence starting voltage, (3) low practical driving voltage, and (4) particularly long lifetime. [Solving Means] An organic EL device including at least a anode, a hole transport layer, a light-emitting layer, a hole blocking layer, an electron transport layer, and a cathode in this order, characterized in that the hole blocking layer includes a compound having a benzoazole structure represented by the following general formula (1). (In the formula, Ar1 and Ar2 may be the same or different from each other and each represent a hydrogen atom, a deuterium atom, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted fused polycyclic aromatic group, or a substituted or unsubstituted aromatic heterocyclic group. Y1 represents a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted fused polycyclic aromatic group, a substituted or unsubstituted aromatic heterocyclic group, a straight-chained or branched alkyl group that has 1 to 6 carbon atoms and may have a substituent group, a cycloalkyl group that has 5 to 10 carbon atoms and may have a substituent group, or a straight-chained or branched alkenyl group that has 2 to 6 carbon atoms and may have a substituent group. X represents an oxygen atom or a sulfur atom. Z1 and Z2 may be the same or different from each other and each represent a carbon atom or a nitrogen atom).