Low-voltage, high-performance n-channel organic thin-film transistors based on tantalum pentoxide insulator modified by polar polymers

Polar polymers (polyfluorene copolymers, PFN–PBT) with different polarities are utilized to modify the surface of tantalum pentoxide (Ta2O5) insulator in n-channel organic thin-film transistors (OTFTs). A high mobility of 0.55 cm2/Vs, high on/off current ratio of 1.7 × 105, and low threshold voltage of 2.8 V are attained for the OTFT with the modification polymers, the performances of which are much better than those of OTFT with only Ta2O5 insulator. The performances of the OTFT with only Ta2O5 insulator are only 0.006 cm2/Vs in mobility, 5 × 103 in on/off ratio, and 12.5 V in threshold voltage. Furthermore, it is found that the threshold voltage of the OTFTs with PFN–PBT modification layer is easily tuned by polarities of the polymers. Further studies show that self-assembly dipole moments in the polymers play an important role in the improvement of the OTFT performances.