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

Abstract 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%.