EL Device Composition for Stable Co-Evaporation
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Solution Overview
Problem
The existing methods for manufacturing organic electroluminescent (EL) devices using the co-evaporation process are costly and inefficient due to the need for multiple evaporation sources and the challenge of maintaining stable characteristics across repeated evaporation processes, as substances with different sublimation temperatures can lead to composition changes in the evaporation source and resulting film changes.
Innovation Solution
A composition for EL devices comprising two organic compounds with a difference in 5% weight loss temperature under low pressure of no more than 50°C, allowing for stable and cost-effective manufacturing by mixing substances with electron-transport and hole-transport properties, which can be evaporated from a single source without significant composition changes, thereby maintaining consistent device characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If co-evaporation of multiple substances is performed using multiple evaporation sources, then the carrier balance and device characteristics can be improved, but the apparatus cost and maintenance complexity increase
Solution Approach 1:
The patent combines multiple substances (host material and emission center substance) into a single mixed composition that can be evaporated from one evaporation source. This merging approach maintains the functional benefits of multiple components while eliminating the need for multiple separate evaporation sources, thereby reducing apparatus complexity and maintenance requirements.
Solution Approach 2:
The patent uses a composite material composition consisting of a host material and an emission center substance mixed in specific ratios. This composite approach allows multiple functional components to be delivered through a single evaporation source, resolving the contradiction between achieving good device characteristics and simplifying the evaporation apparatus.
2Reliability
If substances with different sublimation temperatures are used in co-evaporation, then the functional properties of the light-emitting layer can be optimized, but composition changes occur during repeated evaporation processes
Solution Approach 1:
The patent carefully selects and controls the temperature parameter during evaporation to ensure that both the host material and emission center substance evaporate at appropriate rates despite their different sublimation temperatures. This parameter control maintains stable film composition across repeated evaporation processes while still allowing functional optimization.
Solution Approach 2:
By creating a composite material composition with specifically selected components and ratios, the patent ensures that the mixture evaporates uniformly. The composite structure allows functional property optimization through component selection while maintaining composition stability during repeated use of the evaporation source.
3Manufacturing precision
If multiple evaporation sources are used to co-evaporate substances, then the resolution and lifetime of EL devices can be increased, but the manufacturing cost and time consumption increase
Solution Approach 1:
The patent merges multiple evaporation steps into a single evaporation process by using one evaporation source to deliver a pre-mixed composition of host material and emission center substance. This eliminates the time required to sequentially operate multiple evaporation sources while maintaining precise film formation through controlled evaporation parameters.
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 enables the stable and cost-effective production of EL devices with consistent characteristics by ensuring that the composition of the film does not change significantly during repeated evaporation, reducing capital investment and maintenance efforts while maintaining favorable performance.
Implementation Method 1
Co-evaporation refers to an evaporation method by which different substances are evaporated from different evaporation sources at the same time
Implementation Method 2
substances with different sublimation temperatures can lead to composition changes in the evaporation source
Implementation Method 3
A difference in the 5% weight loss temperature between the at least two kinds of organic compounds measured by thermogravimetry under a pressure of 0.1 Pa or lower is less than or equal to 50° C.
Data Source
AI summary
An object is to provide a novel composition for an EL device. Another object of one embodiment of the present invention is to provide a composition for an EL device capable of easily manufacturing an EL device with stable characteristics. Another object of one embodiment of the present invention is to provide a composition for an EL device capable of manufacturing an EL device with stable characteristics at low cost. The present inventors have studied a composition for an EL device in which different substances are mixed in advance and which does not cause change in characteristics of the EL device even when evaporation is repeated with use of the composition. As a result, a composition for an EL device in which a difference in the 5% weight loss temperature under a pressure lower than or equal to 0.1 Pa between contained substances is less than or equal to 50° C. is provided.