Poly((2-Alkylbenzo[1,2,3]triazole-4,7-diyl)vinylene)s (pBTzVs) synthesized by Stille coupling show different absorption spectra, solid-state morphology, and photovoltaic performance, depending on straight-chain versus branched-chain (pBTzV12 and pBTzV20) pendant substitution. Periodic boundary condition density functional computations show limited alkyl pendant effects on isolated chain electronic properties; however, pendants could influence polymer backbone conjugative planarity and polymer solid film packing. The polymers are electronically ambipolar, with best performance by pBTzV12 with hole and electron transport mobilities of 4.86 x 10(-6) and 1.96 x 10(-6) cm(2) V-1 s(-1), respectively. pBTzV12 gives a smooth film morphology, whereas pBTzV20 gives a very different fibrillar morphology. For ITO/PEDOT:PSS/(1:1 w/w polymer: PC71BM)/LiF/Al devices, pBTzV12 gives power conversion efficiency (PCE) up to 2.87%, and pBTzV20 gives up to PCE = 1.40%; both have open-circuit voltages of V-OC=0.6-0.7 V. (C) 2015 Wiley Periodicals, Inc.