| 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). Bothcompounds exhibited a high degree of thermal stability with decomposition temperatures of 530 °C and425 °C for 1 and 2, respectively. The thin-film structures of 1 and 2 were examined using wide-angle X-raydiffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM). Films of1 and 2 pack in similar triclinic unit cells with the long axes of the molecules nearly perpendicular to thesubstrate. Thin-film transistors (TFTs) based on 1 and 2 exhibit contact-corrected linear regime hole mobilityas high as 0.5 cm2/Vs and 0.1 cm2/Vs, respectively. The specific contact resistance at high gate voltagesfor gold top contacts was 2 × 104 Ω cm and 3 × 104 Ω 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 comparisonto pentacene. Variable temperature measurements revealed activation energies as low as 22 and 27 meVfor 1 and 2, respectively. The temperature and gate voltage dependence of the mobility are discussed interms of a double exponential distribution of trap states and a model accounting for the layered structureof the organic films. The enhanced air and thermal stability over pentacene, combined with good electricalperformance characteristics, make 2 a promising candidate for future organic TFT applications.
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