Ambipolar field-effect transistors with bilayered thiophene/phenylene co-oligomers

Bilayered organic field-effect transistors were fabricated by successive vapor-depositions of 1,4-bis{5-[4-(trifluoromethyl)phenyl]thiophene-2-yl}benzene (AC5-CF3) and 5,5″-bis(4-biphenylyl)-2,2′:5′,2″-terthiophene (BP3T). With decreasing thickness of the n-type AC5-CF3 film in contact with the dielectric layer, ambipolar characteristics were improved under both positive and negative gate biases. Two types of asymmetric source/drain electrodes were prepared by either obliquely shadowed lamination or mask-shifted depositions of AlLi and Au. The latter method in which the device was characterized without exposure to air after the electrode deposition of AlLi resulted in remarkable improvement of ambipolarity and reduction of leak currents. Finally, optimized ambipolar mobilities of μe = 5.00 × 10−2 and μh = 1.56 × 10−2 cm2 V−1 s−1) were obtained with 5-nm-thick AC5-CF3 and 30-nm-thick BP3T.

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► Bilayered organic field-effect transistors were fabricated by vapor-deposition.
► n- and p-type thiophene/phenylene co-oligomer derivatives were used.
► Well-balanced ambipolar characteristics were obtained by thinning the n-type layer.
► Fabrication of asymmetric electrodes was improved for device performances.