Soft Nanoelectronic Devices Based on Novel 2D Nanomaterials and Self-assembled Organic Semiconductors

다국어 초록 (Multilingual Abstract)

Recent advances in electronic device are focused on a fabrication of flexible and stretchable electronic gadgets in a low-cost and sustainable ways. The fabrication of flexible and stretchable electronic devices is highly challenging using inorganic or Si-based electronic materials due to its fragile nature upon a strain. Utilization of solution-processable organic materials including small molecules and polymer in organic field effect transistors (OFETs), light emitting diodes, and solar cells, facilitates a low-cost, large-area, cheap, and environment-friendly mass production for the fabrication of flexible and stretchable electronic devices. Conjugated small molecules and polymers continue to be studied intensively as semiconducting and conducting materials due to its tunability of their electronic and optoelectronic properties. Graphene, a single layer of two-dimensional (2D) carbon atoms in a honeycomb lattice, has attracted enormous attention due to its unique electronic, optical, thermal, and mechanical properties. It has an extremely high charge carrier mobility (~ 200,000 cm2V–1s–1), an optical transmittance of 97.7%, a theoretical sheet resistance of 30 Ω/sq, a high fracture strain resistance greater than 20%, and chemical stability. These features make it highly promising for applications in flexible electronics and energy conversion devices, including touch screens, field-effect transistors (FETs), capacitors, batteries, solar cells, and light-emitting diodes (LEDs). However, the zero-band gap, small optical absorption, and chemical inertness have limited its practical application in switching and optoelectronic devices. Similar to graphene, transition metal dichalcogenides (TMDCs) are 2D materials stacked by van der Waals forces. Contrary to graphene, which does not have a bandgap energy, TMDCs have tunable bandgaps unlike to graphene. Typically, bulk TMDCs show indirect bandgap. On the other hand, the bandgap of TMDCs gradually decrease to one monolayer.
Herein, I present a forward-looking my research results which are mainly focused on the interface studies between organic electronic materials and 2D nanomaterials including graphene and MoSe2, because of the importance of the mechanism and the behavior of electrical property change when organic electronic materials and 2D nanomaterials comes together in the electronic device system. When it comes to the interface study between heterogeneous electronic materials, doping of organic semiconductor and 2D nanomaterials is one of the important steps to enhance the electrical performance. Especially, n-doping of organic semiconductor is more challenging than p-doping because the n-dopants have to show a very low ionization potential to enable electrons to be transferred effectively, which renders most possible candidates unstable in air. Among the various doping strategies, surface transfer doping technique has been investigated for graphene and MoSe2 to modify or enhance their electrical or optoelectrical properties without severe damage on the surface of matrix. In addition, new carbon-based materials with honey comb structure or graphitic structure applying heterogenous atoms such as nitrogen (nitrogen doped reduced graphene oxide and 2D polyaniline) are explored to figure out their unique electrical properties and potential of electronic application. The experimental results and discussion in this thesis represent a forward-looking insight in charge transport behavior when organic electronic materials and 2D nanomaterials make junction together and pave the way of the applicability of organic semiconductors in conventional microelectronic infrastructures, which will lead to progress in the realization of soft nanoelectronic devices.

목차 (Table of Contents)

• Abstract 1
• Contents 2
• List of Figures and Tables 4
• Chapter 1. Introduction to the Interface Between Graphene and Organic Electronic Materials 17
• 1.1. Research Background 17
• 1.2. Synthesis of Graphene and Two-Dimensional Transition Metal Dichalcogenides (2D TMDCs) 18
• 1.3. Electronic Properties of Graphene and 2D TMDCs 19
• 1.4. Surface Transfer Doping Using Organic Dopants 20
• 1.5. Applications Using the Combination of Organic Electronic Materials and Graphene and 2D TMDCs 20
• 1.6 References 22
• Chapter 2. Graphene-ruthenium Complex Hybrid Photodetectors With Ultrahigh Photoresponsivity 26
• 2.1. Introduction 26
• 2.2. Experimental Section 27
• 2.3. Results and Discussion 28
• 2.4. Conclusion 32
• 2.5. References 32
• Chapter 3. Flexible Organic Phototransistor Array with Enhanced Responsivity via Metal-Ligand Charge Transfer 40
• 3.1. Introduction 40
• 3.2. Experimental Section 41
• 3.3. Results and Discussion 42
• 3.4. Conclusion 47
• 3.5 References 48
• Chapter 4. Chemically Robust Ambipolar Organic Transistor Array Directly Patterned by Photolithography 55
• 4.1. Introduction 55
• 4.2. Experimental Section 56
• 4.3. Results and Discussion 59
• 4.4. Conclusion 64
• 4.5. References 65
• Chapter 5. Reduced Pyronin B Doping on Graphene and Organic Semiconductor 81
• 5.1. Introduction 81
• 5.2. Experimental Section 82
• 5.3. Results and Discussion 84
• 5.4. Conclusion 87
• 5.5. References 87
• Chapter 6. Highly Enhanced Optoelectronic Properties in MoSe2 with Reduced Organic Cationic Dye as Molecular N-Dopant 96
• 6.1. Introduction 96
• 6.2. Experimental Section 97
• 6.3. Results and Discussion 98
• 6.4. Conclusion 102
• 6.5. References 102
• Chapter 7. Nitrogen-Doped Graphene Nanoplatelets from Simple Solution Edge-Functionalization for n-Type Field-Effect Transistors 109
• 7.1. Introduction 109
• 7.2. Experimental Section 110
• 7.3. Results and Discussion 111
• 7.4. Conclusion 117
• 7.5. References 118
• Chapter 8. Two-dimensional Polyaniline From Carbonized Organic Single Crystals in Solid State 127
• 8.1. Introduction 127
• 8.2. Experimental Section 127
• 8.3. Results and Discussion 128
• 8.4. Conclusion 132
• 8.5. References 132
• Chapter 9. Summary and Perspectives 146
• Acknowledgments 149
• 감사의 글 150
• Curriculum Vitae 152