Original Article

Polymer Journal (2015) 47, 733–738; doi:10.1038/pj.2015.61; published online 19 August 2015

Synthesis of new D-A polymers containing disilanobithiophene donor and application to bulk heterojunction polymer solar cells

Makoto Nakashima1, Takanori Otsura2, Hiroyoshi Naito2 and Joji Ohshita1

  1. 1Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima, Japan
  2. 2Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University, Osaka, Japan

Correspondence: Professor H Naito, Department of Physics and Electronics, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Osaka 599-8531, Japan. E-mail: naito@pe.osakafu-u.ac.jp; Professor J Ohshita, Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan. E-mail: jo@hiroshima-u.ac.jp

Received 1 May 2015; Revised 14 July 2015; Accepted 17 July 2015
Advance online publication 19 August 2015

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Abstract

New donor–acceptor-conjugated polymers with disilanobithiophene as the donor and dithienylbenzothiadiazole, thienopyrroledione or diketopyrrolopyrrole as the acceptor were synthesized and their optical and electrochemical properties were investigated. The polymers were black solids and showed broad absorption bands in the visible region. The most red-shifted absorption band having a maximum and an edge of 739nm and 1.4eV, respectively, was obtained when diketopyrrolopyrrole was used as the acceptor. The absorption bands were shifted to lower energies when the spectra of the polymers were measured as films, likely due to the interchain interaction of the polymers in the films. Cyclic voltammetry studies of the polymer films were also carried out. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels based on the anodic peak onsets and the optical band gaps were −5.1 to −5.5 and −3.5 to −3.7eV, respectively, depending on the acceptor structures. Bulk heterojunction polymer solar cells that used the present polymers as host material (indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS)/disilane-bridged bithiophene-polymer:PC71BM/Ca/Al) were fabricated, and a maximal power conversion efficiency of 2.49% was achieved based on the polymer with bis(hexylthienyl)benzothiadiazole as the acceptor.