Synthesis and Applications of Cyano-Vinylene-Based Polymers Containing Cyclopentadithiophene and Dithienosilole Units for Photovoltaic Cells

Abstract

Two beta-cyano-thiophenevinylene-based polymers containing cyclopentadithiophene (CPDT-CN) and dithienosilole (DTS-CN) units were synthesized via Stille coupling reaction with Pd(PPh(3))(4) as a catalyst. The effects of the bridged atoms (C and Si) and cyano-vinylene groups on their thermal, optical, electrochemical, charge transporting, and photovoltaic properties were investigated. Both polymers possessed the highest occupied molecular orbital (HOMO) levels of about -5.30 eV and the lowest unoccupied molecular orbital (LUMO) levels of about -3.60 eV, and covered broad absorption ranges with narrow optical band gaps (ca. 1.6 eV). The bulk heterojunction polymer solar cell (PSC) devices containing an active layer of electron-donor polymers (CPDT-CN and DTS-CN) blended with an electron-acceptor, that is, [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(61)BM) or [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM), in different weight ratios were explored under 100 mW/cm(2) of AM 1.5 white-light illumination. The PSC device based on DTS-CN:PC(71)BM (1:2 w/w) exhibited a best power conversion efficiency (PCE) value of 2.25% with V(oc) = 0.74 V, J(sc) = 8.39 mA/cm(2), and FF = 0.36. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3417-3425, 2011