Synthesis and characterization Naphtho[2,1-b:3,4-b']dithiophene-based organic semiconducting molecules for organic electronics

Abstract

Thienoacenes represent an intriguing class of organic semiconducting molecules with potential applications in organic electronics. Some of thienoacenes have been reported with high charge carrier mobility in organic field-effect transistors (OFET). OFETs based on naphtho[2,1-b:3,4-b’]dithiophene (NDT) exhibited moderate device performance and low-band gap donor-acceptor copolymers based on NDT showed a promising solar power conversion efficiency. In this thesis, four novel series of thienoacenes based on naphtho[2,1-b:3,4-b’]dithiophene backbone were designed and synthesized for OFET applications. Firstly, a novel series of p-type semiconducting naphthodithieno[3,2-b]thiophene derivatives (NDTT-n) composed of six-fused aromatic rings were designed and synthesized (Figure 1). The OFETs based on NDTT-10, and NDTT-12 fabricated by vacuum deposition showed a hole mobility of 0.22 and 0.13 cm2/(Vs), respectively with Ion/Ioff above 107 after annealing at 80 oC. Secondly, the derivatives of NDT fused with benzene rings at the flanks of thiophene, namely NBBT-n (Figure 2) were also designed and synthesized. OFETs based on NBBTF-10 fabricated by vacuum deposition exhibited a hole mobility of 0.35 cm2/(Vs) with a current on/off ratio of 106 107 after annealing at 160 oC. Further extension of π-conjugation of NDTT by incorporating with fused thiophenes leading to a new NBTBT-n series was also developed (Figure 3). The OFETs fabricated by NBTBT-10 showed the hole mobility up to 0.25 cm2/(Vs) with a current on/off ratio of 105 106 after annealing at 220 oC. Lastly, two dimensionally π-extended, butterfly-shaped thienoacenes (Figure 4) were also synthesized. The OFETs based on SMB-10 fabricated by spin-coating showed the best performance in this series with an average mobility of 0.027 cm2/(Vs) for five devices and the highest mobility of 0.038 cm2/(Vs) with a current on/off ratio of 106 107 by from chloroform. Key words: organic semiconducting molecules, organic field-effect transistor, thienoacene, charge carrier mobility.

Date of Award	25 Feb 2015
Original language	English
Supervisor	Ricky M S WONG (Supervisor)