Studies of n-Channel Organic Field-Effect Transistors Based on Naphthalene Diimide-Based Copolymers

Thesis (Master's)--University of Washington, 2023I report n-channel organic field-effect transistors fabricated by PNDITz, PNDITS and a series of NDI-based random copolymers, TSxBS, where x = 0, 10, 20, 50, consisting of naphthalene diimide (NDI), triselenophene (TS), and biselenophene (BS) to demonstrate their electrical properties. The PNDITz OFETs demonstrated poor electron mobility and high threshold voltage, whereas the PNDITS OFETs showed enhanced electron mobility (>10-2 cm2/Vs) with ambipolar transport properties. To hinder the hole transport properties, we tuned the composition of donor moieties in the TSxBS random copolymers, resulting in enhanced n-channel properties as a higher BS ratio was adopted. As the composition of the BS moiety increased to 50%, the material was demonstrated as a pure n-type semiconducting polymer. The OFET exhibited an increasing trend of on/off ratio and decreasing trend of threshold voltage with the higher BS ratio. The performance of the OFET electron mobility based on TSxBS showed a nonlinear trend relative to the BS ratio, and the performance was optimized with TS10BS exhibiting the highest electron mobility of 1.11x10-1cm2/Vs. Our works describe the strategy to design effective n-type polymers in terms of electrical properties suitable for efficient OFETs