Synthesis and photovoltaic properties of alkylthio phenyl substituted benzodifuran (BDF)-based conjugated polymers

- Two new alkylthio phenyl substituted benzodifuran (BDF)-based polymers-BDFPS-FFQx and BDFPS-HFQx, were synthesized and characterized in detail.
- The HOMO energy levels have been fine-tuned by incorporation of alkylthio and F atoms (−5.35 eV for BDFPS-FFQx and −5.31 eV BDFPS-HFQx).
- Blending with PC71BM, the device based on BDFPS-FFQx has shown a moderate PCE of 4.62%, the best PCE of 5.16% was obtained for BDFPS-HFQx.

In this work, alkylthio group has been used to modify the BDF core as the central building block. Combined with FFQx and HFQx acceptor, two new polymers, named BDFPS-FFQx and BDFPS-HFQx, were designed and characterized in detail. Both polymers exhibit broad absorption in the UV-vis region covered from 300 to 800 nm. The cyclic voltammetry (CV) results suggest that the common effect of alkylthio and fluorine atom could effectively decrease the molecular energy levels. PSCs deliver PCEs of 4.62% and 5.16% for BDFPS-FFQx and BDFPS-HFQx under the illumination of AM1.5, 100 mW cm−2, respectively. Compared with BDFPS-FFQx, the more balanced and higher hole/electron mobility of BDFPS-HFQx greatly contribute to Jsc and FF. Furthermore, the more suitable nanoscale phase separation for exciton dissociation at the polymer and PC71BM interface also plays a vital role in improving photovoltaic performance.

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