Over 14% efficiency all-polymer solar cells enabled by a low bandgap polymer acceptor with low energy loss and efficient charge separation

Obtaining both high open-circuit voltage (Voc) and short-circuit current density (Jsc) has been a major challenge for efficient all-polymer solar cells (all-PSCs). Herein, we developed a polymer acceptor PF5-Y5 with excellent optical absorption capability (onset extend to ~880 nm and maximum absorption coefficient exceeding 105 cm−1 in film), high electron mobility (3.18 × 10−3 cm2 V−1 s−1) and high LUMO level (-3.84 eV) to address such challenge. As a result, the PBDB-T:PF5-Y5-based all-PSCs achieved a high power conversion efficiency of up to 14.45% with both a high Voc (0.946 V) and a high Jsc (20.65 mA cm-2), due to the high and broad absorption coverage, small energy loss (0.57 eV) and efficient charge generation and transport in the device, which are among the best values in all-PSCs field. In addition, the all-PSC show a ~15% improvement in PCE compared to its counterpart small molecule acceptor (Y5)-based device. Our results suggest that PF5-Y5 is a very promising polymer acceptor candidate for applications in efficient all-PSCs.