Synthesis of medium bandgap copolymers based on benzotriazole for non-fullerene organic solar cells

Three new copolymer donors based on DCN-alt FTAZ PT-68, PT-810-H, and PT-810-L were synthesized by adjusting the alkyl chains and molecular weight. The copolymers showed deep highest occupied molecular orbital (HOMO) levels of about - 5.50 eV due to introducing fluorine atoms and cyano electron-withdrawing groups. Therefore, devices based on the copolymers as donors and ITIC as acceptors had high open-circuit voltages (V-OC) exceeding 1.00 V. Due to a dicyanodistyrylbenzene (DCN) unit providing rigid and extended conjugation and reducing the backbone torsion, the blended films had high hole mobility values of about 2.50 x 10(-3) cm(2) V-1 s(-1). Devices with the PT-810: ITIC blended film had the highest power conversion efficiency (PCE) of 7.03%, with an open-circuit voltage of 1.04 V, a short-circuit current density of 12.25 mA/cm(2), and a fill factor of 55%. These results provide guidance for the design of high-efficiency photovoltaic materials.