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2022 | Book

Flexible OLEDs

Fundamental and Novel Practical Technologies

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About this book

This book offers a wealth of knowledge and information about the fundamental and practical aspects of flexible organic light-emitting diode (OLED) devices. The book provides an overview of these devices by considering their merits and business potential, the history of their research and development, the fundamental technology, and required properties for materials, devices, processes, and future trends of flexible OLED devices. The practical sections describe novel, cutting-edge expertise for flexible substrates, gas barriers, encapsulation, novel electrodes, and on-demand patterning for OLED devices. Applications of the technologies of ultra-thin glass, stainless steel foil, and barrier films are described as flexible substrates. The book also explains features such as dry-barrier layers, wet-barrier layers, multi-layer barrier structures, dam-fill encapsulation, thin film encapsulation (TFE), and laminating encapsulation. In addition, there are explanations of novel electrodes and on-demand ink-jet patterning, both of which are applicable to flexible OLED devices. As the novel electrodes, transparent conducting polymer, silver nanowire (AgNW), metal-mesh and roll-to-roll (R2R) process technologies are included. The know-how that is described here is applicable to flexible devices, not only for OLEDs, OPVs, OTFTs, and others but also for sensors, wearable devices, robots, and healthcare devices. The information contained in this valuable book is useful for all scientists, engineers, and managers who are interested in the field of flexible devices.

Table of Contents

Frontmatter
Chapter 1. Introduction
Abstract
A flexible OLED (Organic Light Emitting Diode) is becoming one of the important key devices in the current IT society supporting our life. The business of flexible OLEDs keeps a significant portion of the current display business and is predicted to make a vigorous expansion. This chapter describes the overview of the current situation and the future’s potential of flexible OLEDs.
Mitsuhiro Koden
Chapter 2. Fundamentals of Flexible OLEDs
Abstract
This chapter describes the fundamental technologies of flexible OLEDs. Sect. 2.1 describes the fundamentals of OLEDs, which include emission mechanism, device structures, encapsulations, and driving methods. Sects. 2.2 and 2.3 describe typical device structures and typical fabrication processes of flexible OLEDs, respectively. Sect. 2.4 describes required properties for flexible OLEDs.
Mitsuhiro Koden
Chapter 3. History of Flexible OLEDs
Abstract
A flexible OLED has already been reported in 1992, though the technological level was still primitive. Research and development on flexible OLEDs have been activated around 2010. In such development, various prototypes of flexible OLED displays and lighting were reported. The first products of flexible OLED display and lighting were commercialized in 2013, respectively. At present (in 2022), flexible OLEDs are mainly applied to smartphones and will increase their applications to various displays such as TV and PC, lighting, wearable devices, healthcare devices, robots, etc., in future. This chapter overviews such active developments and commercialization of flexible OLEDs.
Mitsuhiro Koden
Chapter 4. Flexible Substrates
Abstract
Flexible substrate is one of the important key components for flexible OLED devise. Sect. 4.1 describes requirements for flexible substrates in flexible OLED devices because flexible substrates need to possess not only flexibility but also various features such as gas barrier property, temperature stability, chemical stability, size stability, surface smoothness, etc. Later, Sects. 4.2, 4.3, 4.4, and 4.5 review three actual flexible substrates for flexible OLED devices, describing ultra-thin glass, stainless steel foil, and barrier film, accompanied by novel research and development on these technologies in our research group (Research Group for Flexible Technologies) of Yamagata University (Japan). These sections describe not only features about these flexible substrates but also applications to flexible OLED devices.
Mitsuhiro Koden
Chapter 5. Gas Barrier Technologies
Abstract
Gas barrier technologies are key technologies in flexile OLED devices, being essentially related with the storage reliability. Indeed, if a gas barrier technology applied to flexible OLED device is poor, the storage lifetime of the device is extremely short by penetration of gases such as H2O. In flexible OLED devices, gas barrier technologies are applied to flexible substrates and encapsulations. This chapter describes evaluation methods for gas barrier properties and various gas barrier technologies that are applied to flexible substrates and encapsulations, while the encapsulating technologies are also described in Chap. 6 in more detail. Novel gas barrier technologies developed by our research group (Research Group for Flexible Technologies) in Yamagata University (Japan) are also described.
Mitsuhiro Koden
Chapter 6. Encapsulating Technologies
Abstract
Flexible OLEDs require flexible encapsulation technologies that are essentially different from encapsulation technologies for rigid OLED devices. Flexible encapsulation technologies need to have not only sufficient gas barrier ability but also thin thickness, flexibility, etc. Typical flexible encapsulation technologies are dam-fill, TFE (thin film encapsulation) and laminating. This chapter describes these three technologies, accompanying with novel research and development on these technologies in our research group (Research Group for Flexible Technologies) of Yamagata University (Japan).
Mitsuhiro Koden
Chapter 7. Novel Electrode Technologies
Abstract
Current common transparent electrodes for OLED devices are ITO (indium tin oxide) and IZO (indium zinc oxide) which are usually fabricated by sheet-to-sheet sputtering and photolithography. However, these electrodes have issues in cost and the compatibility with flexible devices. Based on such background, this chapter describes several non-ITO electrodes, which are transparent conducting polymer, silver nanowire (AgNW) and implanted metal-mesh electrodes, and roll-to-roll (R2R) fabrications of ITO and IZO.
Mitsuhiro Koden
Chapter 8. OLEDs with On-Demand Patterns by Ink-Jet Printing
Abstract
In addition to current major OLED applications such as mobile phones, large-size TVs, etc., one of other promising application fields might be OLED lighting devices with certain design patterns. Such OLED devices can be applied to various products such as direction indicators, emergency signs, labels, packaging, advertisements, souvenirs, name plates, name tags, etc. For fabricating such OLEDs, on-demand patterning of OLEDs was developed by patterning of insulators fabricated by ink-jet printing by Sugimoto et al. of our research group (Research Group for Flexible Technologies) in Yamagata University (Japan). The developed OLEDs with on-demand patterns show comparable performances with OLEDs without the patterned insulators. By preventing ink spreading, we achieved high-resolution patterns with L/S = 61/62 μm, which is almost comparable with 400 dpi.
Mitsuhiro Koden
Metadata
Title
Flexible OLEDs
Author
Prof. Dr. Mitsuhiro Koden
Copyright Year
2022
Publisher
Springer Nature Singapore
Electronic ISBN
978-981-19-3544-2
Print ISBN
978-981-19-3543-5
DOI
https://doi.org/10.1007/978-981-19-3544-2