Control of doping state and conductance of PEDOT-based film and its applications in organic transistors

Abstract

The conducting polymers have received great attention based on their features such as light weight, flexibility, controllable film color, and large-area processability. Not like polymer semiconductors, intrinsically conducting polymers are already commercialized. And eco-friendly processes using water and alcohol-based solvents are possible. The optical and electrical properties of conducting polymers can be controlled by using doping state control and various post treatments. Although highly conductive conducting polymers are hard to utilize as semiconductors in transistor devices, some studies showed that the conducting polymers can be used as high-mobility semiconductors in electrochemical devices using liquid electrolytes. However, the problems of liquid electrolytes such as leakage, evaporation, and contamination limit the application of electrochemical devices. In this study, organic transistors with solid-state and dry-environment-operational characteristics were demonstrated. In order to obtain semiconducting characteristics in conducting polymers, studies about control of doping state in conducting polymer were conducted. Adding on to doping-controlled conducting polymers, nonvolatile ionic liquid-based solid-state electrolyte, ionogel, was used to achieve high performance transistors with low-voltage operation without above problems. The previously reported solid-state electrolyte used conducting polymer electrolyte-gated transistor devices showed very low on-to-off current ratio. By using enamine base, doping-controlled conducting polymer film showed high-mobility, high on-to-off current ratio with sub-5 V operation with two-dimensional channel formation in dry environment. In addition, control of doping state with stronger reducing agent, amidine base, was conducted and the amidine-treated conducting polymer-based transistor showed negative threshold voltage and well-resolved linear and saturation currents with conventional field-effect transistor devices. Through the studies about doping-controlled conducting polymers, I investigated material property against doping state, and suggested new application of conducting polymers as semiconductor. Not only chemical dedoping, various doping and dedoping methodologies, such as secondary doping treatment and high-energy radioactive ray irradiation, were demonstrated. This study will open a way to use conducting polymers as semiconductors in solid-state devices and will widen the application of conducting polymer.