Inkjet-printed unipolar n-type transistors on polymer substrates based on dicyanomethylene-substituted diketopyrrolopyrrole quinoidal compounds

Abstract The development of printable and air-stable unipolar n-type semiconductors remains a critical issue in the field of organic electronics in view of n-type transistors being indispensable components in the manufacture of low-power-consumption complementary (CMOS type) integrated circuits. In this work, we report on two dicyanomethylene-substituted diketopyrrolopyrrole derivatives with different alkyl side chains (DCM-DPP-C 13 and DCM-DPP-C 16 ) for n-type transistors. Compared with DCM-DPP-C 16, the side chain branching point in DCM-DPP-C 13 was moved further away from the conjugated backbone. Both materials showed promising electron mobility above 0.1 cm 2 /VS in air with remarkably low threshold voltages (−3 V – 2 V) on spin-coated bottom-contact bottom-gated devices on silicon substrates. Contrary to our original expectation, the average electron mobility of DCM-DPP-C 16 (0.2 cm 2 /VS) was higher than that of DCM-DPP-C 13 (0.12 cm 2 /VS) due to the bigger crystalline domains in the thin film of the former compound. We investigated the inkjet printability of these two compounds as well, and bottom-contact top-gated transistors were successfully fabricated on flexible PET substrates. Widely used Cytop was employed as the gate dielectric. Ag gate electrodes were readily inkjet printed on the gate dielectric by using a thin layer of Nafion as an adhesion promoter. DCM-DPP-C 16 demonstrated an excellent inkjet-ability with good uniformity and reproducibility. An average electron mobility around 0.1 cm 2 /VS was achieved in air. This is an important step toward the fabrication of large-area organic CMOS logic circuits with low cost.