We report the synthesis, morphology, and optoelectronic device applications of novel biaxially extended quaterthiophene- (4T-) and octithiophene- (8T-) vinylene conjugated polymers, P4TV and P8TV, synthesized via Stille coupling reactions. P4TV and P8TV exhibited smaller energy band gaps of 1.69 and 1.78 eV than that of parent polythiophenes, respectively, due to the reduced conformation distortion by the vinylene linkage. The HOMO energy levels of P4TV and P8TV were -5.02 and -5.13 eV, respectively, resulting in air stable device performance. The highest field effect hole mobilities of P4TV and P8TV were 0.12 and 0.0018 cm(2) V-1 s(-1), respectively, with on/off ratios around 10(4)-10(5). The higher carrier mobility of P4TV was related to its ordered structure as evidenced from the TEM, AFM, and grazing incidence X-ray diffraction results. The power conversion efficiency (PCE) of the P4TV/PC71BM based photovoltaic cells (PV) under the illumination of AM 1.5G (100 mW/cm(2)) was 4.04%, which was significantly higher than that of P8TV/PC71BM with 2.69%, due to its superior charge transport ability. However, P8TV had a better environmental stability attributed to its low-lying HOMO energy level. These above results demonstrate that biaxially extended thiophene-vinylene conjugated copolymers could be promising materials for high performance organic electronic device applications.