Combined Molecular Design, Morphology Control, and Device Engineering Towards Superior Organic Semiconductors

Department of Energy Engineering (Energy Engineering)Owing to the valuable features of organic polymers, such as inexpensive materials, ease of mass production, light-flexible properties, in recent days, the organic semiconductors have attracted significant research interests of challenging scientists in conducting and semiconducting organic polymers. The main concept of the conjugation of conducting organic polymers has occurred from the continuously connected pz-orbitals of sp2(or sp)-hybridized carbon atoms from the alternating sequence of single and multi-bonds (double and triple bonds) in the polymeric backbone. Based on the concept of conjugation structure, until now, many ??-conjugated organic polymers and small molecules have been designed with great expectation for various advents of the electronic application, like as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs). Over the past decades, many pioneering research groups have paid attention to the design and development of novel organic semiconductors for next generated optoelectronic devices due to the aforementioned advantages of organic semiconductors. Moreover, many research interests have been concentrated on not only the invention of completely brand-new molecular structures but also fine-tuning of the existing molecular structures with marginal trade-off their outstanding own properties. In particular, the fine-tuning approaches are quite effective methods because the parent molecules had exhibited remarkable performances in optoelectronic devices. Therefore, the modified molecules usually have shown comparable or much better performances compared to parent molecules. In terms of modification of backbone, I present the article describes the synthesis and characterization as well as OFET characteristics of a collection of TBIG-based polymers with varied compositions between TBIG and IIG accepting segments and bithiophene counterpart donor. Secondly, based on the designed and synthesized with 2-ethylhexyl and 5-ethylnonyl side chains on the CPDT core, I demonstrated its effectiveness of side-chain engineering for the CPDT-based polymers and CPDT-based small molecules on the OFET performance and semi-transparent OPV performance, respectively. Finally, to fine-tuning of molecular properties, the substituents have been used without the sacrificial of the mainstream of organic semiconductors. The most universal substituent, fluorine with single proton, I investigated the constitutional isomeric effects on the photovoltaic performances via atomic level insight from the computational simulation and nano-second transient absorption spectroscopy.clos