A series of new polythiophene derivatives containing a thiazole ring as an electron deficient unit were successfully synthesized via Stille coupling reactions. Synthesized polymers were classified into two types (H-shape packing and A-shape packing) based on their interdigitated packing structure induced by different side chain configurations. The thiophene derivatives that contained a thiazole unit (PT50Tz50, PTz100, and PTTz) exhibited much better thermal stability than did the full thiophene polymers (PT100 and PTT). The polymers containing the thiazole unit (PTz100 and PTTz) showed a red-shifted absorption spectrum with clear vibronic structure. In addition, the XRD and AFM results showed that the polymers containing the thiazole unit and interdigitated H-shape exhibited much better ordered and connected intermolecular structures than did other polymers. The improved intermolecular ordering and surface morphologies directly facilitated charge carrier transport in thin film transistor (TFT) devices, without introducing charge traps, and yielded higher solar cell performance. Among these polymers, the PTTz copolymer exhibited the best TFT performance (mu = 0.050 cm(2) V(-1) s(-1), on/off ratio = 10(6), and V(th) = -2 V) and solar cell performance (PCE = 1.39%, J(sc) = 6.58 mA cm(-2), and V(oc) = 0.58 V). (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2886-2898, 2011