2,7-carbazolenevinylene-based oligomer thin-film transistors: High mobility through structural ordering

We have fabricated organic field-effect transistors based on thin films of 2,7-carbazole oligomeric semiconductors 1,4-bis(vinylene-(N-hexyl-2-carbazole))phenylene (CPC), 1,4-bis(vinylene-(N-methyl-7'-hexyl-2'-carbazole))benzene (RCPCR), N-hexyl-2,7-bis(vinylene-(N-hexyl-2-carbazole))carbazole (CCC), and N-methyl-2,7-bis(vinylene-(7-hexyl-N-methyl-2-carbazole))carbazole (RCCCR). The organic semiconductors are deposited by thermal evaporation on bare and chemically modified silicon dioxide surfaces (SiO2/Si) held at different temperatures varying from 25 to 200 degrees C during deposition. The resulting thin films have been characterized using UV-vis and Fourier-transform infrared spectroscopies, scanning electron microscopy, and X-ray diffraction, and the observed top-contact transistor performances have been correlated with thin-film properties. We found that these new pi-conjugated oligomers can form highly ordered structures and reach high hole mobilities. Devices using CPC as the active semiconductor have exhibited mobilities as high as 0.3 cm(2) V-1 s(-1) with on/off current ratios of up to 10(7). These features make CPC and 2,7-carbazolenevinylene-based oligomers attractive candidates for device applications.