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

Rathinam Raja; Shengkai Luo; Chuen-Yo Hsiow; Syang-Peng Rwei; Leeyih Wang

doi:10.3390/polym9070272

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

Polymers (Basel). 2017 Jul 7;9(7):272. doi: 10.3390/polym9070272.

Authors

Rathinam Raja¹, Shengkai Luo^{2

3}, Chuen-Yo Hsiow⁴, Syang-Peng Rwei⁵, Leeyih Wang^{6

7}

Affiliations

¹ Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan. rajaorgchem80@gmail.com.
² Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan. t101320391@ntut.org.tw.
³ Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei 10608, Taiwan. t101320391@ntut.org.tw.
⁴ Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan. chuenyohsiow@ntu.edu.tw.
⁵ Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei 10608, Taiwan. f10714@ntut.edu.tw.
⁶ Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan. leewang@ntu.edu.tw.
⁷ Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan. leewang@ntu.edu.tw.

Abstract

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-C₇₁-butyric acid methyl ester (PC₇₁BM) as acceptor with an inverted device structure of ITO/ZnO/PDTBSeVTT-2TF:PC₇₁BM/V₂O₅/Ag. The processing temperature of blend solution for preparing PDTBSeVTT-2TF:PC₇₁BM 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 PC₇₁BM and thus increasing the donor/acceptor interface.

Keywords: benzoselenodiazole; difluoro-bithiophene; polymer solar cell; vinyl-terthiophene.