Thin-film transistors based on liquid-crystalline tetrafluorophenylter thiophene derivatives: thin-film structure and carrier transport

✍ Scribed by Fapei Zhang; Masahiro Funahashi; Nobuyuki Tamaoki

• Book ID: 103877230
• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 840 KB
• Volume: 10
• Category: Article
• ISSN: 1566-1199
• DOI: 10.1016/j.orgel.2008.10.020

✦ Synopsis

The authors fabricated thin films by solution processes using liquid-crystalline (LC) semiconductors, 5-alkyl-5''-(4-hexyltetrafluorophenyl)-2,2':5',2''-terthiophene (2-5). Films of 5-propyl-5''-(4-hexyltetrafluorophenyl)-2,2':5',2''-terthiophene (2) show similar molecular packing as their non-fluorinated counterparts. However, the degree of molecular packing ordering from X-ray diffraction measurement is higher, and the films exhibit a more crystal-like structure. Moreover, fluorination has a remarkable effect on their mesomorphic behaviors. Films of 2 consist of large size LC domains (in the range of 100 lm) at room temperature. Thin-film transistors (TFTs) of 2 show p-type operation with good hole mobility up to 0.027 cm 2 /Vs as well as improved operation stability under ambient conditions and high on/off ratio. Tetrafluorophenyl substitution leads to lowering of HOMO energy by 0.15 eV for 2 and 0.35 eV for 5, resulting in operation stability. Variable-temperature current-voltage measurements indicate intrinsic carrier transport in films of 2.