Controlling the molecular orientation of a novel diketopyrrolopyrrole-based organic conjugated polymer for enhancing the performance of organic field-effect transistors

Abstract

A novel organic conjugated copolymer p(DPP-BZC) was utilized as a solution-processable organic semiconductor and its large area of the unidirectionally oriented thin film was fabricated by the Ribbon-shaped floating film transfer (FTM) method. Organic field-effect transistors (OFETs fabricated using oriented thin films of this polymer demonstrated a clear p-type semiconducting behaviour and anisotropic charge carrier transport. A maximum orientation with a dichroic ratio of 5.1 was obtained in the FTM-processed thin film under optimized conduction with liquid substrate viscosity, temperature and polymer solution concentration of 6.12 cst, 50 °C and 3% (w/v), respectively. Out-of-plane XRD and in-plane GIXD results revealed that oriented thin films of this copolymer are semicrystalline and adopt purely edge-on on conformation. The implication of surface modification of Si/SiO 2 gate dielectric utilizing HMDS. OTS and CYTOP on the charge carrier transport revealed that substrate with high-surface-energy hampers the on/off ratio, operating voltage and charge carrier mobility (μ). On the other hand, Si/SiO 2 substrate treated with CYTOP having relatively lower surface energy demonstrated the best device performance with the highest μ of 2.7 x 10 −2 cm 2 /Vs, which is > 30 times higher as compared to that of its non-oriented spin-coated device counterparts an μ of 8.0 x 10 −4 cm 2 /Vs. • Synthesis of novel conjugated polymer p(DPP-BZC) and utilization of its oriented thin films for OFET fabrication. • Utilizing the FTM technique an oriented thin film with DR of 5.1 was achieved under optimized conditions. • Purely edge-on orientation in the oriented film was confirmed by XRD and GIXD. • Surface passivation was found to be desired and amongst various surface modifiers used, CYTOP exhibited the best performance. • OFETs utilizing oriented thin films exhibited the mobility of 2.7 x 10 −2 cm 2 /Vs, which was >30 times higher than corresponding spin-coated devices.