An efficient polymer acceptor with fluorinated linkers enables all polymer solar cells with an efficiency of 15.7%

Abstract

Despite the significant progress in all-polymer solar cells (all-PSCs) in recent years, obtaining both high open-circuit voltage (V_OC) and short-circuit current density (J_SC) simultaneously has been a challenging issue. Herein, a novel polymer acceptor PY-DF was developed by polymerizing small molecule acceptor (SMA) monomers with difluorothiophene linkers. Compared to non-fluorinated PYT, PY-DF exhibits a more coplanar and rigid molecular conformation, which leads to better intra-molecular conjugation and enhanced interchain packing, resulting in improved electron mobility and reduced energetic disorder. Furthermore, PY-DF exhibits a relatively up-shifted lowest unoccupied molecular orbital (LUMO) energy level (−3.76 eV) than PYT (−3.80 eV), which is favorable for improving V_OC. In addition, the polymer acceptor demonstrates good miscibility with polymer donor, thus leading to optimized phase segregation for superior exciton dissociation and charge transport. As a result, the PY-DF-based all-PSCs achieved a higher PCE of 15.7% with simultaneously enhanced J_SC (23.1 mA cm⁻²) and V_OC (0.97 V) in comparison with PYT-based all-PSCs (PCE = 13.2%, J_SC = 21.7 mA cm⁻², and V_OC = 0.93 V). This work provides a promising polymer acceptor for all-PSCs and shows that fluorination of linkers is a potential strategy to build high-performance polymer acceptors.