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

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 mu m, 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.