Investigation of Organic Conjugated Materials to Understand the Structure-Property Relationships for High-Performance Organic Electronics

Abstract

Since the time when conjugated materials were found to have semiconducting properties with the p-orbital overlapping through the backbone, there have been a lot of research to develop high-performing materials for organic electronic applications, such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), and organic field-effect transistors (OFETs) with the advantages of light weight, mechanical flexibility, structural versatility, and facile manufacture with easy solution processing, regarding the energy level, bandgap and the charge transporting behaviors. In OFET system, the factors to obtain a high performance are turned out to be (1) proper energy level placements allowing a spontaneous charge flow between electrode and semiconducting materials used in the system, (2) effective intramolecular charge transfer by utilizing a push-pull architecture and an longer effective p-orbital overlapping between the building blocks in a conjugated backbone, (3) favorable intermolecular interactions affording effective intermolecular transport through the π-stacked system and good processability, (4) favorable morphological and (5) microstructural characteristics of the films to allow a good interlayer compatibility and satisfy an optimal crystallinity and crystalline orientation. With the structural versatility and tunability of organic materials, it is important to understand how structural factors of conjugated materials govern the molecular properties related to the device performance and charge transport behaviors for a logical design of high-performing organic semiconductors in electronic applications with desirable characteristics. Therefore, in this dissertation, I tried to figure out the relationships between the factors governing the device performance and charge transport behatiors listed above and molecular structures by assigning structural variations; the first chapter is about the energy level alignment to develop n-type materials by utilizing building blocks considering the electorn-accepting ability, the second chapter regards intermolecular interactions of conjugated materials to enhance noncovalent interactions or solution processability, and the last chapter introduces how regiochemistry can affect the intramolecular charge transfer, film morphology and microstructural characteristics. These findings can be integrated to establish molecular design strategies for high-performance OFETs, and further utilized to expand the application to OPVs and Li+-ion battery system.