Browsing by Author "Mukhopadhyay, T."

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    Air-stable n-channel diketopyrrolopyrrole-diketopyrrolopyrrole oligomers for high performance ambipolar organic transistors
    (American Chemical Society, 2016) Mukhopadhyay, T.; Puttaraju, B.; Senanayak, S. P.; Sadhanala, A.; Friend, R.; Faber, H. A.; Anthopoulos, T. D.; Salzner, U.; Meyer A.; Patil, S.
    n-channel organic semiconductors are prone to oxidation upon exposed to ambient conditions. Herein, we report design and synthesis of diketopyrrolopyrrole (DPP)-based oligomers for ambipolar organic thin-film transistors (OFETs) with excellent air and bias stability at ambient conditions. The cyclic voltammetry measurements reveal exceptional electrochemical stability during the redox cycle of oligomers. Structural properties including aggregation, crystallinity, and morphology in thin film were investigated by UV-visible spectroscopy, atomic force microscopy (AFM), thin-film X-ray diffraction (XRD), and grazing incidence small-angle X-ray scattering (GISAXS) measurements. AFM reveals morphological changes induced by different processing conditions whereas GISAXS measurements show an increase in the population of face-on oriented crystallites in films subjected to a combination of solvent and thermal treatments. These measurements also highlight the significance of chalcogen atom from sulfur to selenium on the photophysical, optical, electronic, and solid-state properties of DPP-DPP oligomers. Charge carrier mobilities of the oligomers were investigated by fabricating top-gate bottom-contact (TG-BC) thin-film transistors by annealing the thin films under various conditions. Combined solvent and thermal annealing of DPP-DPP oligomer thin films results in consistent electron mobilities as high as ∼0.2 cm2 V-1 s-1 with an on/off ratio exceeding 104. Field-effect behavior was retained for up to ∼4 weeks, which illustrates remarkable air and bias stability. This work paves the way toward the development of n-channel DPP-DPP-based oligomers exhibiting retention of field-effect behavior with superior stability at ambient conditions.
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    Electrochemical stability and ambipolar charge transport in diketopyrrolopyrrole-based organic materials
    (ACS, 2019) Ray, S.; Panidi, J.; Mukhopadhyay, T.; Salzner, Ulrike; Anthopoulos, T. D.; Patil, S.
    An important strategy for realizing flexible complementary circuits with organic semiconductors is to achieve balanced ambipolar charge transport properties with reduced anisotropy. Here, we present a series of star-shaped diketopyrrolopyrrole (DPP)-based organic materials synthesized for improved intermolecular charge transport while retaining the ambipolar charge transport properties of their linear counterparts. Steady-state UV−visible spectroscopic studies confirm that the oligomers are highly aggregated in the thin film as evidenced from appearance of prominent vibronic features and red-shifted absorption bands. Ambipolar transport properties of these materials were verified in organic field-effect transistors (OFETs). The results show that the star-shaped DPP systems have the potential to outperform their linear counterparts in devices