Study of contact resistance of high-mobility organic transistors through comparisons

• Contact resistance (Rc) of high-performance organic field-effect transistors was systematically investigated.
• Influences of electron acceptor layer, active-layer thickness, and alkyl side chain on Rc were studied.
• The lowest Rc of 110 W·cm was attained and high mobility of 6 cm2/Vs was kept for polycrystalline OFETs at short channels.

Realization of high-frequency low-cost organic electronics requires high-mobility organic field-effect transistors (OFETs) with short channels, where influence of contact resistance becomes more serious than either lower mobility or longer channel devices. To reduce the contact resistance, we systematically and quantitatively investigate the influence of the lowest unoccupied molecular orbital (LUMO) level of an electron acceptor layer, the active layer thickness, and the side chain of active layer itself on contact resistance of top-contact high-mobility OFETs through a series of comparative analysis. We find that the acceptor of 1,3,4,5,7,8-hexafluoro tetracyano naphtha quinodimethane (F6TNAP) with a deeper LUMO level is efficient for carrier injection and that the bulk resistance plays an important role in such devices. By optimizing the parameters, we get the lowest contact resistance of only 110 Ω cm, and thus recorded effective mobility of 8.0 cm2/V s is attained for polycrystalline thin film transistors and still kept as high as 6 cm2/V s at shorter channel lengths.

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