Studies on doping methods of graphene-based materials for electronic and electrochemical devices

Abstract

Graphene has been widely utilized in electronic devices as a transparent electrode. Charge transfer doping maintains the integrity of graphene's hexagonal structure because the dopants are adsorbed on the surface. Commonly used dopants include acids (HNO3, HCl, H2SO4), metal chlorides (AuCl3, SoCl2, RhCl3), and polymers (Nafion, TETA). Conventional one-side doping has shown low doping strength. Additionally, the doping effect diminishes over time because the dopant can decompose depending on the temperature or solvent, or evaporate over time. Therefore, to enhance doping effectiveness and stability, dual-side doping was employed, positioning dopants on both sides of the graphene. In Chapter 2, the optical and electrical properties, as well as the stability of dual-side doped graphene, were investigated and compared to one-side doped graphene. Furthermore, by using dual-side doped graphene as a hole-transport layer in silicon-based Schottky photodiodes, the Schottky barrier was increased, leading to excellent performance. GQDs are defined as C-based quantum dots that exhibits quantum confinement effect, which was less than 100 nm in diameter and 10 nm in thickness. It has high surface area and excellent dispersibility. The characteristics of electronic band structure are significantly influenced by the edge effect. In chapter 3, we synthesized amide-functionalized, nitrogen-doped graphene quantum dots from fumaronitrile. Nitrogen atoms were integrated into the carbon lattice and formed functional groups such as amide, carboxyl, hydroxyl, and amine on the edge. By adjusting the precursor amount, we controlled the quantities of amide and carboxyl functional groups. DFT simulation results showed that while the adsorption energy of oxygen was similar, the desorption energy of oxygen in the amide group was much lower than in the carboxyl group. The optimized nitrogen-doped, amide-functionalized GQDs exhibited excellent electrochemical activity, characterized by the lowest overpotential and Tafel slope. In this paper, the electrical, optical, and chemical properties of graphene-based materials were controlled through doping. This control enabled the excellent performance of energy devices by fine-tuning the properties of graphene-based materials.