New isoindigo and di(thienyl)ethylene-containing -extended conjugated polymers with different branched side chains were synthesized to investigate their physical properties and device performance in thin-film transistors and photovoltaic cells. 11-Butyltricosane (S3) and 11-heptyltricosane (S6) groups were used as side-chain moieties tethered to isoindigo units. The linking groups between the polymer backbone and bifurcation point in the branched side chain differ in the two polymers (i.e., PIDTE-S3 and PIDTE-S6). The polymers bearing S6 side chains showed much better charge transport behavior than those with S3 side chains. Thermally annealed PIDTE-S6 film exhibited an outstanding hole mobility of 4.07 cm(2) V-1 s(-1) under ambient conditions. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of PIDTE-S3 and (6,6)-phenyl C61-butyric acid methyl ester demonstrated promising device performance with a power conversion efficiency in the range of 4.9-5.0%. (c) 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015, 53, 1226-1234