Novel Two-Dimensional Conjugated Polymer Containing Fluorinated Bithiophene as Donor and Benzoselenodiazole as Acceptor Units with Vinyl-Terthiophene Pendants for Polymer Photovoltaic Cells

Novel two-dimensional conjugated copolymer, abbreviated as PDTBSeVTT-2TF, containing electron-deficient 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) unit, conjugated vinyl-terthiophene (VTT) side chain and 3,3′-difluoro-2,2′-bithiophene (2TF) was designed and synthesized using microwave-assisted Stille cross-coupling polymerization. UV–visible absorption and cyclic voltammetry studies revealed that this copolymer possesses a strong and broad absorption in the range of 300–800 nm and a narrow optical bandgap (E(g)) of 1.57 eV with low-lying HOMO and LUMO energy levels. Further, the bulk heterojunction polymer solar cells (PSCs) were fabricated using PDTBSeVTT-2TF as donor and [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC(71)BM/V(2)O(5)/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC(71)BM active layer showed obvious impact on the photovoltaic performance of solar devices. The cell fabricated from the blend solution at 65 °C exhibited enhanced power conversion efficiencies (PCE) of 5.11% with a J(sc) of 10.99 mA/cm(−2) compared with the one at 50 °C, which had a PCE of 4.69% with a J(sc) of 10.10 mA/cm(−2). This enhancement is due to the dissolution of PDTBSeVTT-2TF clusters into single molecules and small aggregates, improving the miscibility between the polymer and PC(71)BM and thus increasing the donor/acceptor interface.