Spacer length effect of tributylsilyl-terminated side chains on the properties of poly(diketopyrrolopyrrole-alt-terthiophene)s

Abstract

To meet the needs of the future commercialization of organic thin-film transistors (OTFTs), several issues of conjugated polymers (CPs), including limited mobility, low solubility, and high cost owing to the complicated structures, ought to be addressed. Herein, seven poly(diketopyrrolopyrrole-alt-terthiophene)s appending easy made tributylsilylalkyl side chains with different alkyl spacer lengths, named SiCm, in which m (3–8 and 10) represents the number of C atom between the Si atom and conjugated backbone, were synthesized. All the polymers are soluble in o-xylene with a solubility of at least 10 mg mL⁻¹ at room temperature. The effect of the position of the Si branching point on the properties of the polymers was systematically investigated. The film microstructures and thus the OTFT performance of polymers can be adjusted by varying the alkyl spacer length between the Si branching point and conjugated backbone. As the spacer length increases, the mobility first rises and then drops, in line with the evolution trend of intermolecular packing order and film morphology. The polymer SiC6 with a C6 spacer (m = 6) exhibited the best device performance. A hole mobility up to 2.69 cm² V⁻¹ s⁻¹ in the saturation regime was demonstrated for SiC6-based OTFTs processed via bar-coating from o-xylene. The current work paves the way to high mobility CPs that possess facile synthesis and good processability in non-chlorinated solvents.