2-Dodecyl benzotriazole (BTz) and benzothiadiazole (BTd) containing copolymers poly(4-(2-dodecyl-2H-benzo[d][1,2,3]triazol-4-yl)benzo[c][1,2,5]thiadiazole (P1), poly(4-(5-(2-dodecyl-7-(thiophen-2yl)-2H-benzo[d][1,2,3]triazol-4-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (P2) and poly(4-(5-(2-dodecyl-7-(4-hexylthiophen-2-yl)-2H-benzo[d] [1,2,3]triazol-4-yl)-3-hexylthiophen-2-yl) benzo[c][1,2,5] thiadiazole (P3) were synthesized via Suzuki polycondensation. We report the application of conjugated copolymers in bulk heterojunction photovoltaic devices. When the copolymers were blended with [6,6]phenyl-C-61-butyric acid methyl ester (PCBM), P2 showed the best performance with an open circuit voltage (V,), a short-circuit current density (J(sc)) and a power conversion efficiency (PCE) of 0.45 V, 3.48 mA cm(-2) and 0.45%, respectively, under AM 1.5G illumination conditions (100 mW cm(-2)). The hole mobilities of the devices were calculated from J-V curves using Space Charge Limited Current (SCLC) method and the maximum mobility value was found to be 3.15 x 10(-5) cm(2) V-1 s(-1) the P2:PCBM blend. (C) 2012 Elsevier Ltd. All rights reserved.