Applications of novel dithienothiophene- and 2,7-carbazole-based conjugated polymers with surface-modified ZnO nanoparticles for organic photovoltaic cells

Abstract

Two kinds of novel conjugated polymers containing 2,7-carbazole, thiophene, and fused-dithienothiophene rings as backbones bearing acid-protected and benzoic acid pendants (PC1 and PC2, respectively) were utilized for organic solar cell applications. The absorption spectra of these polymers (in both solutions and solid films) showed an absorption range at 300-580 nm. Furthermore, ZnO nanoparticles were synthesized and surface-modified with pyridyl surfactants (ZnOpy) to be ca. 3-4 nm. The pyridyl surfactants of ZnOpy nanoparticles (as electron acceptors to partially replace expensive electron acceptor PCBM) not only induce supramolecular interactions with benzoic acid pendants of polymer PC2 via H-bonds, but also enhance the homogeneous dispersions of ZnOpy nanoparticles in polymer PC2. Thus, the ternary systems of PC1-N2/ZnOpy/PCBM in weight ratios of 1:0.05:1 and 1:0.1:1 were investigated in bulk heterojunction polymer solar cells (PSCs). Under the standard illumination of AM 1.5, 100 mW/cm(2), the best power conversion efficiency (PCE) of the PSC cell containing a polymer blend of PC2/ZnOpy/PCBM = 1:0.05:1 reached PCE = 0.55%, with J(sc) = 2.11 mA/cm(2), V(oc) = 0.88 V, and FF = 29.4%. (C) 2011 Elsevier B.V. All rights reserved.