Graphene for Flexible Lighting and Displays PDF by Tae-Woo Lee


Graphene for Flexible Lighting and Displays
Edited by Tae-Woo Lee

Graphene for flexible lighting and displays


Contributors vii
About the editor ix
Preface xi
Acknowledgments xiii
1. Introduction 1
Tae-Woo Lee and Sung-Joo Kwon
References 2

2. Structure and properties of graphene 5
Yong Seok Choi, Je Min Yoo and Byung Hee Hong
2.1 Structure of graphene 5
2.2 Synthesis of graphene 8
2.3 Electronic band structure of graphene 11
2.4 Optical properties of graphene 14
2.5 Electrical properties of graphene 16
2.6 Mechanical properties of graphene 22
References 23
Further reading 26

3. Preparation of graphene electrode 27
Wencai Ren
3.1 Solution casting of graphene oxide 27
3.2 Transfer methods of CVD grown graphene 33
References 52
4. Graphene doping for electrode application 59
Amirhossein Hasani and Soo Young Kim
4.1 Chemical doping of graphene 59
4.2 Metal oxide doping of graphene 65
4.3 Stability of the doped graphene electrodes 67
Acknowledgments 70
References 70
5. Technical issues and integration scheme for graphene electrode
OLED panels 73
Jaehyun Moon, Jin-Wook Shin, Hyunsu Cho, Jun-Han Han,
Byoung-Hwa Kwon, Jeong-Ik Lee and Nam Sung Cho
5.1 Introduction 73
5.2 Graphene preparation for OLED applications 74
5.3 Technical issues of OLEDs having graphene film electrodes 74
5.4 Integration schemes for realizing large area graphene electrode
OLED panels 87
5.5 Summary and future outlook 94
Acknowledgments 95
References 95
Further reading 98
6. Graphene-based buffer layers for light-emitting diodes 99
Quyet Van Le and Soo Young Kim
6.1 Introduction 99
6.2 Graphene oxide buffer layer 99
6.3 Graphene-based composite buffer layer 110
6.4 Conclusion 113
References 113
7. Graphene-based quantum dot emitters for light-emitting diodes 117
Park Minsu, Yoon Hyewon and Jeon Seokwoo
7.1 Introduction to graphene quantum dots 117
7.2 Synthetic strategies for GQDs 121
7.3 Toward highly efficient fluorescence from GQDs 133
7.4 Lighting applications of GQDs 138
7.5 Summary and outlooks 143
References 145
8. Graphene-based composite emitter 151
Hong Hee Kim and Won Kook Choi
8.1 Grapheneemetal/metal oxide hybrid composite 151
8.2 Graphene-based composite emitter 152
References 170
9. Stretchable graphene electrodes 175
Shuyan Qi and Nan Liu
9.1 Introduction 175
9.2 Preparation of stretchable graphene electrodes 177
9.3 Applications of stretchable graphene electrodes 191
9.4 Summary and outlook 199
References 201
10. Conclusions and outlook 205
References 207
Index 209

The demand for lighting and display technologies is driving research to diversify the forms of devices. Future lighting and displays should be bendable, foldable, and stretchable to satisfy consumers’ desire for convenience and efficient use of space. Flexible components of lighting and display devices should be mechanically tolerant of repeated severe flexion. However, conventional light-emitting diodes (LEDs) for lighting and displays are mostly fabricated on a brittle transparent conducting oxide electrode (e.g., indium tin oxide [ITO]), which has poor tolerance to mechanical strain. Therefore, alternative flexible transparent conducting materials have been evaluated to replace ITO.

Graphene is a two-dimensional single-atom-thick sheet of carbon atoms in an sp2-bonded hexagonal configuration. Graphene’s unique structure yields excellent electrical and optical properties as well as mechanical robustness, so it is regarded as a strong candidate for use as a flexible electrode in lighting and displays. However, pristine graphene has several characteristics that limit its practical applications in flexible self-emissive LEDs. Its sheet resistance Rs is too high, and its work function (WF) is too low for graphene to be effective as an anode in LEDs. Chemical doping of graphene can control Rs and WF, so the charge injection from graphene electrode to overlying layers in LEDs can be significantly improved. As a result of appropriate chemical doping, especially with organic and polymeric dopants, the luminous properties of organic light-emitting diodes (OLEDs) based on graphene electrodes have been increased to be comparable to those of OLEDs that use ITO electrodes. The doping can also make graphene very stable against moisture, organic solvents, and acids.

Graphene-based materials can be used as an interfacial layer to improve the charge injection in LEDs. Pristine graphene has no bandgap, but chemical functionalization (e.g., oxidation, hydrogenation) can induce one and provide an intermediate step for charge injection, so the luminous properties of LEDs can be improved. Graphene quantum dots (QDs) can also themselves be light emitters. The graphene QDs have advantages (e.g., nontoxicity, high chemical stability, high carrier mobility) over inorganic QDs.

Graphene can also be stretchable, so it can be used in stretchable electronics and displays. To date, several structural modifications or composite with other stretchable conducting materials have increased the stretchability of graphene and allowed it to be used in stretchable electronics.

This book will cover the fundamental electrical, optical, and mechanical properties of graphene; the preparation of pristine graphene, doped graphene, graphene-derived interfacial and graphene QD emitting materials and their composites; and treatments to modify its electrical properties by adsorbed molecules and deposited films. Then the book presents the use of flexible or stretchable electrodes with graphene or its composites in various LEDs for lighting and displays (e.g., OLEDs, inorganic LEDs, QD-LEDs, and halide perovskite LEDs). It will also describe the use of graphenederived materials as interfacial buffer layers or as light-emitting layers in LEDs.

This book is written by leading experts who are working on graphene-based materials and optoelectronic devices. It provides in-depth information on use of graphene in light-emitting devices. The overall goal of this book is to provide comprehensive information about fundamental properties of graphene; on methods to synthesize graphene; on techniques to prepare graphene electrodes and composite electrodes; on methods to dope graphene electrodes; and on applications of graphene-based flexible electrodes, interfacial buffer layers, nanoscale emitters, and graphene-based stretchable electrodes. The ultimate objective is to inspire further research on practical optoelectronics applications of graphene.

This book will be of interest to the large community of researchers who are working on applying graphene in various electronic and optoelectronic devices and may stimulate research to develop practical uses of graphene sheets in next-generation displays and lightings. The book will additionally provide future prospects and suggest further directions for research on graphene-based next-generation displays and lightings. Therefore, this book will be helpful for students, professors, researchers, and engineers who work on graphene or graphene-derived materials or on graphene-based displays and lighting technology.

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