Improved photovoltaic properties of the copolymers based on diketopyrrolopyrrole with broad absorption and high open-circuit voltage

A series of donor acceptor conjugated polymers based on the alkylthienyl-benzodithiophene (BDTT) as an electron-rich unit, and diketopyrrolopyrrole (DPP) incorporated in backbone or side chain as electron deficient units have been synthesized and applied in polymer solar cells. Compared with the binary copolymers, random terpolymers exhibit a broader absorption range. By controlling the ratio of the electron-deficient units, both photophysical, electrochemical properties, lamellar distance, pi-pi* stacking distance and the photovoltaic properties of the random terpolymers were changed dramatically. Bulk heterojunction polymer solar cells based on the copolymers as the electron donors and (6,6)-phenyl-C-61-butyric acid methyl ester as the acceptor were fabricated. The power conversion efficiency of 4.46% was obtained from the terpolymer (PBDTT-DPP-TTDPP). Optimization via solution vapor annealing, the binary copolymer (PBUTT-TTDPP) showed the best power conversion efficiency of 4.74% with a short-circuit current of 10.63 mA cm(-2), a high open-circuit voltage of 0.88 V and a fill factor of 51.0%. (C) 2016 Elsevier Ltd. All rights reserved.