Toward Eco-Friendly Solvent-Processable DPP-Based Conjugated Polymers with Siloxane Branched Side Chains: Synthesis, Properties, and Ambipolar Field-Effect Transistor Characteristics

Abstract

The role of side chains in molecular design for polymer semiconductors has received widespread attention, as it has a profound impact on material processing, film quality, and performance of organic optoelectronic devices. With the development of modern organic optoelectronic technology and the demand for industrial production, green processing methods for materials and devices have attracted more attention. Herein, three conjugated polymer semiconductors based on diketopyrrolopyrrole (DPP) and selenophen were designed and synthesized with side chains exhibiting characteristics of double polysiloxane-terminated groups. The corresponding polymers T1-PDPPSi-Se and T3-PDPPSi-Se have branched chain sites at C2 and C4 in the side chains, respectively. The proper design of the double polysiloxane-terminated side chain enabled the copolymers not only to have higher molecular weights but also to exhibit excellent solubility, especially in “green” solvents. Polymer semiconductor films were prepared using low-toxicity non-chlorinated solvents (toluene and hexane), and their organic field-effect transistors (OFETs) were fabricated, exhibiting ambipolar transport behavior. The devices based on polymers T1-PDPPSi-Se, T31-PDPPSi-Se (medium molecular weight), and T32-PDPPSi-Se (high molecular weight) without being processed had the maximum hole/electron mobilities of 2.34 × 10^–2/0.38 × 10^–3, 2.65 × 10^–2/1.6 × 10^–3, and 4.07 × 10^–2/4.7 × 10^–3cm²V^–1s^–1, respectively. Moreover, non-chlorinated reagent-cast films had the same orders of magnitude mobility values as chloroform-cast films, which were important for greener device processing. Thin films of three materials probed by GIWAXS reveal a random lamellar direction and not the π–π direction. This penetrates the reason why its mobility is lower than that of linear siloxane-modified polymers. These results may be used for reference in the molecular design of hybrid side chain-modified semiconducting conjugated polymers.