The new low-band gap polymers comprising C-, Si-, or N-bridged dithiophene and alkoxy-modified 2,1,3-benzooxadiazole units for bulk heterojunction solar cells

Abstract

In this study, we used Stille coupling polymerization to synthesize a series of new low-band gap-conjugated polymersPCyTBO, PCySiTBO, and PCyNTBOcomprising mainly electron-rich C-, Si-, and N-bridged dithiophene units in conjugation with electron-deficient alkoxy-modified 2,1,3-benzooxadiazole moieties. The highest occupied molecular orbital energy levels of these polymers become higher as the electron-donating ability of C-, Si-, or N-bridged dithiophene units increases. These polymers also displayed excellent thermal stability and broad spectral absorptions, with PCySiTBO revealing some crystallinity. As a result, the photovoltaic device incorporating the PCySiTBO/PC71BM (1:1) blend system and 1,8-diiodooctane (2 vol %) as an additive exhibited excellent performance, under AM 1.5 G irradiation (100 mW cm-2), with a value of Voc of 0.64 V, a short-circuit current density of 13.8 mA cm-2, a fill factor of 0.57, and a promising power conversion efficiency of 5.0%. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012