LAUSR

Abstract Direct arylation polymerization (DAP) is emerging as a promising green, cheap, simple, and efficient environment friendly method for synthesizing conjugated polymers without involving any organometallic reagent. We report fluorene based novel cross-conjugated alternate and random copolymers for polymer solar cells (PSCs), which were synthesized by DAP and/or Yamamoto polymerization under appropriate reaction conditions to obtain high molecular weight. These cross-conjugated polymers possess absorption maxima in the range of 490–520 nm and have narrow band gap (1.7–2.05 eV) which is suitable for bulk heterojuntion (BHJ) type organic solar cells. Among the synthesized polymers, the highest number average molecular weight (Mn) i.e. 43.1 kg mol−1 was obtained for polymer P2b (poly((9H-fluoren-9-ylidene)methylene)bis((2-ethylhexyl)sulfane)-alt-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)), and so good polymeric films were formed for P2b. Thus, BHJ films were prepared for P2b for device performance studies and the morphology of these films was studied by atomic force microscopy (AFM). Polymer P2b was blended with the fullerene derivative [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) in different ratios and under the illumination of solar simulator with Air Mass global (AM 1.5G) irradiated at 100 mW cm−2. Power conversion efficiency (PCE) of 1.4% has been achieved for BHJs in ratio of 1:2 of P2b: PC71BM in simply processed devices. This result indicates that cross-conjugated polymers can be tapped as potential donors for BHJs as the PCE obtained is the highest among this type of cross-conjugated polymers.