Theoretical design of high-mobility bithiophene imide (BTI) derivative polymeric semiconductors

There has been increasing interest in organic semiconducting polymers for use in organic electronics due to their reasonable charge mobility, low-cost and environmental stability. In this work, bithiophene-imide (BTI) comonomers are designed systematically in silico by combining the electron acceptor BTI unit with different types and numbers of interior thiophene units as electron donor groups. The effects of functionalization of BTI unit on the electronic, optical and charge mobility properties of comonomers are investigated by density functional theory (DFT) calculations. The presence of nitro substitution on the BTI unit lowers the optical band gaps and results in high hole mobilities. The copolymer-6 is estimated to be the best p-type organic semiconductor among all studied copolymers with the highest hole mobility of 1.31 cm² V⁻¹ s⁻¹. The adsorption isotherms of the copolymers for the H₂O, CO₂ and O₂ adsorbate molecules are analyzed by Monte Carlo simulations to elucidate the air and water stabilities for better device performances.