Effect of the length and branching point of alkyl side chains on DPP-thieno[3,2-b]thiophene copolymers for organic thin-film transistors

Abstract Solid-state packing and polymer orientation are critical for achieving high charge carrier mobility in organic thin-film transistors. Four side chain substituents, 2-octyldodecyl (−20), 4-octyltetradecyl (−22), 2-decyltetradecyl (−24), and 4-decylhexadecyl (−26), were synthesized to study the effect of side chains on the molecular crystallinity and charge transport properties of diketopyrrolopyrrole–thieno[3,2-b]thiophene copolymers (DPPTTs). Achieving high-performance DPP-based polymers not only depends on crystallinity, but also on the appropriate proportions of polymer chain orientations. DPPTT22 and DPPTT26 have more coplanarity of the backbone structure and a shorter π–π stacking distance, but the charge mobilities are limited. The objective of this study is to determine the influence of different side chains on the layer distance and π–π stacking regarding 3D carrier channel formation. However, a favorable morphology is also important to improve the charge mobility. DPPTT24 shows improved mobility due to its suitable edge-on-oriented crystallinity and well-interconnected domains with small grain boundaries.