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

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.