Efficiency enhancement of a fluorinated wide-bandgap polymer for ternary nonfullerene organic solar cells

A fluorinated BDT-TPD-based donor polymer (P1) was synthesized via Suzuki polymerization. P1 shows a wide bandgap (1.9 eV) and a deep highest occupied molecular orbital level (−5.71 eV). Ternary organic solar cells (OSCs) were fabricated from our synthesized polymer donor (P1) and two small molecular nonfullerene acceptors (IT-4F and Y6). The P1:IT-4F binary OSC exhibited a power conversion efficiency (PCE) of 6.59%, with a short-circuit current density (JSC) of 10.36 mA/cm2, open-circuit voltage (VOC) of 0.91 V and a fill factor (FF) of 70%. By contrast, the P1:Y6 binary OSC exhibited a PCE of 10.58% with a JSC of 22.01 mA/cm2, VOC of 0.86 V and FF of 56%. An enhanced PCE of 11.64% was achieved in the ternary OSC with 25 wt% IT-4F incorporated into the acceptors [IT-4F:Y6 (25:75)]; this enhancement was attributed to the improved JSC of 22.97 mA/cm2, VOC of 0.87 V and FF of 58%. Appropriate phase separation could be achieved by incorporating an appropriate amount of IT-4F into the acceptors, which promoted exciton dissociation and charge transport. The PCE improvement of the IT-4F:Y6 (25:75) ternary device was attributed mainly to enhanced photon harvesting and exciton dissociation and to reduced charge recombination.