Research Project Highlight

Pyromellitic Diimide-Ethynylene-Based Homopolymer Film as an N-Channel Organic Field-Effect Transistor Semiconductor

pyromelliticSemiconducting polymers can form thin film by solution process and potentially by printing, enabling the fabrication of plastic electronic devices without the use of photolithography patterning. While many organic molecular solids and polymers can be used as hole-transporter, and the number of electron-transporting molecular solids is growing, there is only a limited number of semiconducting polymers that can be used for electron-transporting organic field-effect transistors. We synthesized and characterized two solution-processable pyromellitic diimide (PyDI)-acetylene-based conjugated homopolymers. The structurally simple polymers were made by connecting adjacent small PyDI cores with short triple bond linkages. Cyclic voltammetry revealed that these polymers have sufficient electron affinity to accept electrons. Absorption spectra revealed that one polymer, with a simple octyl chain, has greater intermolecular interaction or conjugation after forming a thin film, and that film exhibited electron transport in organic field-effect transistor devices with top-gate/bottom-contact architecture. X-ray diffraction (XRD) and atomic force microscopy (AFM) results show that the octyl polymer is amorphous on the bulk scale. The polymer exhibited electron mobility of about 2 × 10–4 cm2 V–1 s–1 with on/off ratio of 103 and is the simplest n-channel polymer yet reported. A 4-trifluoromethylphenethyl side chain did not result in measurable electron mobility. The octyl polymer exhibited negative Seebeck coefficient on the order of −40 μV/K in thermoelectric devices, further substantiating its n-channel activity. The demonstration of electron transport from such a simple polymer has opened a new path for obtaining n-channel semiconducting activity from polymer films.

Related

Organic semiconductors for use in plastic electronic devices and other alternative active circuits such as display backplanes are generally hole-transporters. It is much more challenging to design electron transporters, which are often needed to complete a circuit or even a single device.

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