Optimization of organic device performance with an in situ real-time doping system

Abstract

Semiconductors are an indispensable component of the modern electronics industry. Among them, organic semiconductors are being actively studied to replace silicon-based inorganic semiconductor devices in the field of next-generation electronic devices due to their light weight, flexibility, low process cost, and ease of chemical modification. Despite these characteristics, electrical characteristics are still lower than conventional silicon-based inorganic semiconductors, so they are applied only in some fields such as OLED and are still experiencing difficulties. In order to improve these electrical properties, molecular doping methods have been widely used and research has been conducted. However, most target organic materials for molecular doping are concentrated on polymers, and as the concentration of dopants increases, electrical performance does not continue to increase but decreases under certain conditions, so it takes time and cost to know the optimal performance conditions. Therefore, a new strategy is needed to improve this. In this thesis, we will discuss a study that obtains optimal electrical conductivity by an in situ real-time doping system that can improve the electrical performance of organic small molecules. Chapter 1.1 describes the background knowledge of organic semiconductors and their electrical properties needed to understand study. The electrical properties of organic semiconductors and the advantages of organic small molecules compared to polymers are described. In addition, the definition and measurement method of electrical conductivity are explained. Chapter 1.2 describes molecular doping that can improve low electrical properties, which is a disadvantage of organic semiconductors, and introduces various molecular doping methods. Chapter 2 describes the development of an efficient in situ real-time molecular doping system that can obtain optimal electrical conductivity by analyzing changes in electrical conductivity during doping of organic small molecules. The electrical properties and doping processes could be simultaneously performed through the PCB, and in order to diffuse the dopant F4TCNQ molecules accumulated on the surface of the spiro-OMeTAD film, which is an organic low molecule, a heater was installed on the PCB to increase the temperature of the film during the doping process. As a result, uniformly doped film was obtained. In addition, by measuring electrical properties in real time, it was possible to obtain higher optimal electrical conductivity than that fabricated by the ex situ method without multiple experiments. We find that the presence of neutral dopant molecules and their diffusion into the bulk region are responsible for the decrease in conductivity after optimal conductivity.