Synthesis, field-effect and photovoltaic properties of random difluorobenzothiadiazole-isoindigo electron donor-acceptor polymers

• Two random donor-acceptor polymers with different donor moieties synthesized.
• The polymer with a stronger donor moiety exhibited higher photovoltaic efficiency.
• Decisive influence of donor moiety over the polymer performance demonstrated.

Two random electron donor-acceptor (D-A) polymers comprised of two acceptor moieties, difluorobenzothiadiazole and isoindigo, and one donor moiety (P1 and P2) have been synthesized in good yields to study the effects of donor structures on organic thin-film transistor (OTFT) and bulk-heterojunction organic solar cell (BHJ-OSC) performance. Both polymers possess reasonably good solubility in common processing solvents for organic electronics. P1, which contains a benzodithiophene donor structure, shows poor charge transport ability in OTFTs and low solar power conversion efficiency (PCE) in BHJ-OSC devices with PC71BM acceptor. On the other hand, P2, with a dithienylthieno[3,2-b]thiophene donor moiety, exhibits distinctly higher hole field-effect mobility and significantly much better PCE under similar conditions. These results have demonstrated the decisive influence of donor moiety over the optoelectronic properties of D-A polymers.

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