Synthesis and Photovoltaic Properties of Diketopyrrolopyrrole-Based Donor−Acceptor Copolymers

Abstract

Three kinds of diketopyrrolopyrrole-based donor−acceptor (D-A) type copolymers, poly{9,9-di(2-ethylhexyl)fluorene-2,7-diyl- alt- 3,6-dithien-2-yl-2,5-di(2-ethylhexyl)-pyrrolo[3,4- c ]pyrrole-1,4-dione-5′,5′′-diyl} (PF-DTDPP), poly{ N -(1-decylundecyl)carbazole-2,7-diyl- alt- 3,6-dithien-2-yl-2,5-di(2-ethylhexyl)-pyrrolo[3,4- c ]pyrrole-1,4-dione-5′,5′′-diyl} (PC-DTDPP), and poly{ N -[1-(2-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2- b:2′,3′- d ]pyrrole - 3,6-dithien-2-yl-2,5-di(2-ethylhexyl)-pyrrolo[3,4- c ]pyrrole-1,4-dione-5′,5′′-diyl} (PDTP-DTDPP) were synthesized. By changing the donor segments, the absorption ranges of DTDPP-containing copolymers can be tuned. PF-DTDPP and PC-DTDPP showed absorption bands in the range of 500−700 nm, while PDTP-DTDPP showed broad absorption in the range of 500−1000 nm in the solutions. The power conversion efficiencies (PCE) of the polymer solar cells (PSCs) based on these copolymers and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) were 0.88% (PF-DTDPP), 2.26% (PC-DTDPP), and 1.12% (PDTP-DTDPP), respectively, under the illumination of AM 1.5 (100 mW/cm 2 ). The monochromatic photocurrent responses of the PSCs based on PDTP-DTDPP:PCBM blends extend to the near-infrared region around 1 μm, which makes this material a promising candidate for the application in the multilayer or tandem photovoltaic devices combined with the conventional visible light absorbing materials.