Polymer solar cells are a promising alternative to traditional solar cells made from silicon, as they are less expensive and easier to manufacture. However, their efficiency in converting sunlight into electrical energy is not as good as that of silicon-based solar cells. The limited absorption range of the all-polymer system leads to a significant decrease in the short-circuit current density (Jsc), which in turn affects the problem of improving the PCE.

     To broaden the light absorption of polymer acceptors, herein, benzotriazole is introduced in the core unit of small molecule acceptors and thus two narrow-bandgap polymer acceptors named PTz-BO and PTz-C11 featuring the same molecular backbone and different side-chain length are synthesized.

      The study used the Enlitech solar simulator and the QE-R quantum efficiency measurement system. The results confirm that compared to PTz-C11, the all-PSC based on PTz-BO has slightly lower Jsc, higher open-circuit voltage (Voc), and low voltage loss below 0.50 V. In addition, ternary all-PSCs are constructed by introducing PTz-C11 as a guest component. Thanks to the reduced composite, improved exciton generation and dissociation, and balanced charge transfer, the ternary all-PSCs obtained a high efficiency of 16.58%, with a high  Jsc over 25 mA cm−2 ,  without sacrificing the Voc.

       This work demonstrates the great potential of benzotriazole for the synthesis of efficient narrow-bandgap polymer acceptors.