Synthesis of Organic Semiconductors Based on Fused Heteroacenes for Optoelectronic Applications

Abstract

Organic semiconductors have attracted much interest for future electronic devices such as organic light emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs) and so on due to many potential merits like light weight, low cost, flexibilty and solution processablity. Despite considerable studies for material science and device physics related to organic semiconductors, a better understanding of the efficient molecular design and systemical optimization is highly required for further development of organic electronics. So far, organic semiconductors based on rigid and π-conjugated molecular backbones that synthesized by powerful cross-coupling reaction methodologies have exhibited promising device performance. Among those, especially fused acenes or hetercyclic architecture has many advantages such as strong intermolecular interaction, increased coplanarity, reduced bandgap and good charge carrier transport. However, restricted synthetic methods hinder various modification of electronic properties of organic semiconductors with fused ring systems. In this work, synthesis of organic semiconductors based on such fused or cyclized heteroacenes and their optoelectronic applications are presented. Firstly, a thiophene-fused ladderized heteroacene dye is designed and synthesized via efficienct synthetic pathways. The fused material is used as a metal-free organic photosensitizer for DSSCs and the light harvesting property is characterized. Secondly, a nitrogen-fused cycle, carbazole-based semicondcutor PCDTBT, which is one of promising photoactive p-type polymer in organic bulk-heterojuction solar cells, is modified via incorporation of different electron-deficient units such as bisbenzothiadiazole, naphthothiadiazole and fluorinated benzothiadiazoles for systemical studies of structure-property relationship. The synthetic procedures and characterization of optical and electronic properties in OPVs are presented for each resulting PCDTBT derivative. Finally, a highly π-extended heteroacene, dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene (DTBDT), with α-positions availability is prepared via the synthesis of a key intermediate. The homopolymer and copolymers are synthesized for the first time and their properties are fully characterized. All polymers based on DTBDT are applied as p-type materials for OFETs.