A phthalimide- and diketopyrrolopyrrole-based A1–π–A2 conjugated polymer for high-performance organic thin-film transistors

Abstract

An acceptor–π–acceptor (A₁–π–A₂) type polymer based on phthalimide and diketopyrrolopyrrole units has been designed and synthesized by Stille cross-coupling reaction. The photo-physical, electrochemical and transistor properties have been also investigated. The polymer exhibited broad absorption in the near infrared region and low LUMO/HOMO energy levels. Organic thin-film transistors (OTFTs) devices with common architectures were fabricated to evaluate the device properties. Polymer-based OTFTs devices exhibited n-type charge transfer under vacuum and yielded an electron mobility as high as 0.52 cm² V⁻¹ s⁻¹. This is a record value for n-type polymers based on phthalimide structure. The OTFTs devices were also investigated in air and displayed p-type transporting behavior with a hole mobility of up to 0.13 cm² V⁻¹ s⁻¹. The corresponding thin film morphology and polymer packing were also investigated in detail by atomic force microscopy (AFM) and X-ray diffraction (XRD) to correlate with the mobility. The results showed that the polymer film possessed highly uniform polymer nanofibers, a long-range-ordered lamellar structure and a small π–π stacking distance.