title: p-Channel organic semiconductors based on hybrid acene-thiophene molecules for thin-film transistor applications.
abstract: We report the structural and electrical characterization of two new p-channel organic semiconductors, 5,5'-bis(2-tetracenyl)-2,2'-bithiophene (1) and 5,5'-bis(2-anthracenyl)-2,2'-bithiophene (2). Both compounds exhibited a high degree of thermal stability with decomposition temperatures of 530 degrees C and 425 degrees C for 1 and 2, respectively. The thin-film structures of 1 and 2 were examined using wide-angle X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM). Films of 1 and 2 pack in similar triclinic unit cells with the long axes of the molecules nearly perpendicular to the substrate. Thin-film transistors (TFTs) based on 1 and 2 exhibit contact-corrected linear regime hole mobility as high as 0.5 cm2/Vs and 0.1 cm2/Vs, respectively. The specific contact resistance at high gate voltages for gold top contacts was 2 x 10(4) Ohms cm and 3 x 10(4) Ohms cm for 35 nm thick films of 1 and 2, respectively. Long-term air stability tests revealed less degradation of the electrical properties of 1 and 2 in comparison to pentacene. Variable temperature measurements revealed activation energies as low as 22 and 27 meV for 1 and 2, respectively. The temperature and gate voltage dependence of the mobility are discussed in terms of a double exponential distribution of trap states and a model accounting for the layered structure of the organic films. The enhanced air and thermal stability over pentacene, combined with good electrical performance characteristics, make 2 a promising candidate for future organic TFT applications.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Merlo
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Newman
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Gerlach
authors.forename: Tommie W
authors.initials: TW
authors.lastname: Kelley
authors.forename: Dawn V
authors.initials: DV
authors.lastname: Muyres
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Fritz
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: C Daniel
authors.initials: CD
authors.lastname: Frisbie