Herein, we demonstrate an effective fine-tuning of carrier transport properties in polymer semiconductors by loading fluorine atoms on polymeric pi-systems. To a thienoisoindigo-based conjugated backbones, we introduced dithiophenethene, difluorodithiophenethene, difluorodiphenylethene, and tetrafluorodiphenylethene units affording D-A copolymers, PTIDTE, PTIFDTE, PTIDFPE, and PTITFPE, respectively. PTIDTE and PTIDFPE exhibited unipolar p-channel transport properties with mobilities of 0.24 and 0.11 cm(2) V-1 s(-1), respectively, whereas PTIFDTE and PTITFPE afforded ambipolar transport properties with the highest hole/electron mobilities of 0.072/0.017 cm(2) V-1 s(-1) and 0.017/0.0034 cm(2) V-1 s(-1), respectively. Thin film microstructure studies (AFM and 2D-GIXRD) suggest that more ordered lamellar and predominantly edge-on molecular packing mode formed in the PTIFDTE and PTITFPE thin films though they own inferior surface morphologies. The thienoisoindigo-based polymers' backbone conformations were purposed to interpret their different molecular packing mode in solid state, revealing that single conjugated backbone conformations are much easier to form for PTIFDTE and PTITFPE. (c) 2017 Elsevier Ltd. All rights reserved.