Influence of the Planarity of DPP-BTZ D-A Copolymer Backbone on the Charge Transport Characteristics

Recently, donor-acceptor (D-A) type conjugated copolymers have garnered significant attention due to their high field-effect mobility and ambipolar characteristics, allowing for both p- and n-type charge transport. This presentation focuses on a newly synthesized semiconducting polymer resulting from the copolymerization of diketopyrrolopyrrole (DPP) and benzotriazole (BTZ) units. In order to investigate the influence of the planarity of the polymer backbone on charge transport in DPP-BTZ semiconducting copolymer films, which serve as the active layer in organic field-effect transistors (OFETs), four distinct DPP-BTZ semiconducting copolymers were synthesized, featuring varying ratios of alkyl side-chains to fluoroalkyl side-chains (specifically, alkyl chains: fluoroalkyl chains = 3:7, 5:5, 7:3, and 10:0). The analysis of DPP-BTZ copolymer films was conducted through ultraviolet-visible spectroscopy, grazing incident X-ray diffraction (GIXRD), and density functional theory (DFT) simulations. The experimental findings demonstrate that an increase in the ratio of fluoroalkyl side-chains results in a reduced π-π distance between molecules and an increased torsional angle of the polymer backbone. Conversely, the measured electrical characteristics of DPP-BTZ-based OFETs indicate a reduction in current under identical bias conditions as the ratio of fluoroalkyl side-chains increases. These results emphasize that the torsional angle of the DPP-BTZ copolymer backbone exerts a more significant influence on charge transport properties than the intermolecular distance between molecules. Consequently, it is deduced that enhancing the planarity and rigidity of the polymer backbone is crucial for enabling efficient charge transport in polymer film.