Diketopyrrolopyrrole based small molecular semiconductors containing thiazole units for solution-processed n-channel thin-film transistors

Abstract

In this work, three diketopyrrolopyrrole-based conjugated small molecular semiconductors characterized by the combination of a diketopyrrolopyrrole (DPP) central core, thiazole π-conjugated moiety, and dicyanovinyl end group with different alkyl side chain substituents, 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV were synthesized. These small molecules have a similar narrow band gap of about 1.50 eV and deep LUMO energy level at −4.30 eV. Under ambient conditions, electron mobilities of 0.28 cm2 V−1 s−1, 0.13 cm2 V−1 s−1, 0.25 cm2 V−1 s−1 for solution processed thin films of 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV were obtained, due to high crystallinity and well-organized molecular stacking. Compared with the other two materials, thin films of 2TzDPPA1-2DCV enable the best OFET performance with desirable Ion/Ioff rates exceeding of 107, attribute to the coefficient of smoother film morphology and stronger crystallinity. These results reveal that introducing the thiazole unit into the DPP-based conjugated skeleton is conducive to enhance the crystallinity and tailor LUMO energy levels which ensure good performance and excellent stability of these molecules as active materials for n-channel electronic devices.