A new random D-A copolymer based on two different benzotriazole units as co-acceptors for polymer solar cells

In this work, two different benzotriazole derivatives (BTAZT and BTAZF) have been chosen as co-acceptors with a BDTT donor to build a new random D-A copolymer (PBTAZT-F) for polymer solar cells. Compared with two mono-acceptor (BTAZT or BTAZF) based homogeneous copolymers (PBTAZT and PBTAZF) as well as their physical-blend polymer (PBTAZT/PBTAZF), PBTAZT-F shows much broader absorption band with a larger full-width half-maxima (FWHM) in 400-750 nm due to good complementary of the intramolecular charge transfer absorption from two kinds of D-A structures in single unit, indicating that it can exhibit more efficient light-capturing ability in the visible region. PBTAZT-F based device shows the highest J(sc) among all the polymers, which is attributed to its broad absorption as well as relatively large and balanced charge transport. Thus, it gives the best PCE of 5.58% with a J(sc) of 11.28 mA cm(-2), a V-oc of 0.84 V and a FF of 58.60%. (C) 2018 Elsevier Ltd. All rights reserved.