Abstract
Novel solution-processable dithieno[3,2-d:2′,3′-d]thiophene (DTT) derivatives with alkylated thiophene or alkyl chain substituents, 2,6-bis(5-octylthiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (compound 1), 2,6-bis(5-(2-ethylhexyl)thiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (compound 2), and 2,6-dioctyldithieno[3,2-b:2′,3′-d]thiophene (compound 3), have been synthesized and employed as small molecular organic semiconductors for organic field-effect transistors (OFETs). All compounds exhibited good thermal stability over 290 °C, while different side groups of DTT compounds afforded different melting temperatures. The molecular orbital energy levels were experimentally and theoretically calculated, and their trend was almost the same. The developed compounds were employed as active layers for top-contact/bottom-gate OFETs with average charge carrier mobility as high as 0.10 cm2/Vs and current on/off ratio > 107 in ambient atmosphere. Notably, DTT derivative with linear alkyl chain (-octyl) substituents showed the best device performance. High device performance could be attributed to the large grains and continuous surface coverages as well as high film texture of the corresponding semiconductor films.
Highlights
Studies on organic semiconductors (OSCs) have been conducted for various optoelectronic applications in mechanically flexible, cost-effective, and large-area electronics such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs) [1,2,3,4,5,6,7,8,9,10,11]
Research advances on OFETs have focused on improving the electrical performance and stability of π-bonded organic semiconductors
The microstructure and surface morphology of the thin film semiconductor was characterized by X-ray diffractometer (D8 Advance (TRIO/TWIN), Bruker, Billerica, MA, USA) and atomic force microscope (AFM, Park Systems, Suwon, Korea), respectively
Summary
Studies on organic semiconductors (OSCs) have been conducted for various optoelectronic applications in mechanically flexible, cost-effective, and large-area electronics such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs) [1,2,3,4,5,6,7,8,9,10,11]. There have been several reports in which organic semiconductors exhibited very high electrical performance with carrier mobility > 1–10 cm2/Vs [12,13,14,15,16,17,18,19]. Vegiraju et al reported 3,5-dithioalkyl DTT-based small molecular semiconductors end-capped with diverse fused thiophenes and the resulting solution processed OFETs showed high device performance with hole mobility as high as 2.6 cm2/Vs [47]. To this end, it is worth further developing solution-processable DTT derivatives as OSC for OFETs. In this study, we newly designed and synthesized three DTT-based compounds with terminal alkyl chains (Figure 1). Compound 2, which showed the best average hole mobility, exhibited relatively high XRD peak intensity and smooth terrace-like film morphology, facilitating the extension of the π orbital overlap
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