Precise fluorination of polymeric donors towards efficient non-fullerene organic solar cells with balanced open circuit voltage, short circuit current and fill factor

Three polymer donors named Qx-8F, Qx-10F, and Qx-12F, with similar chemical structures, were synthesized. The energy level of these donors is manipulated by precisely controlling the fluorination sites. We demonstrate that the exciton dissociation efficiency is gradually enhanced from Qx-8F:Y6 to Qx-12F:Y6, leading to improved open circuit voltage VOC and short circuit current density JSC for donors with a higher degree of fluorination. Simultaneously, the trap-assisted recombination or bimolecular recombination intensity is reduced, while the extraction rate is enhanced because of increased charge carrier mobilities, leading to an increase in fill factor for donors with higher amount of fluorine atoms. The optimized device based on Qx-12F with the most fluorine atoms and the non-fullerene acceptor Y6 shows the highest power conversion efficiency of 15.21%, with a VOC of 0.85 V, JSC of 24.55 mA cm−2, and fill factor of 72.88%. It is further demonstrated that the optimized ternary device based on the Qx-12F:PM6:Y6 blend provides a power conversion efficiency of 16.32%.