A new low-bandgap polymer acceptor based on benzotriazole for efficient all-polymer solar cells

The rational design of polymer acceptors with strong and broad absorption is critical to improve photovoltaic performance. In this work, a new polymer acceptor PY9-T based on heptacyclic benzotriazole (Y9-C16) as a building block and thiophene unit as the linking unit was synthesized, which exhibited a low bandgap (1.37 eV) and a high extinction coefficient of the neat film (1.44×105 cm−1). When PY9-T was blended with the wide bandgap polymer donor PBDB-T, the all-polymer solar cells (APSCs) showed a high power conversion efficiency (PCE) of 10.45% with both high open circuit voltage of 0.881 V and short-circuit current density of 19.82 mA/cm2. In addition, APSCs based on PY9-T show good thermal stability, as evidenced by slight changes morphologies when annealed at 100 °C. These results suggest that Y9-C16 provides a new building block to develop efficient and stable polymer acceptors.