Impact of the Bonding Sites at the Inner or Outer π-Bridged Positions for Non-Fullerene Acceptors

Two A-pi-D-pi-A-type non-fullerene acceptors (IDT-ToFIC and IDT-TiFIC) with 5-hexylthienyl chains substituted at the inner and outer beta-positions of the thiophene pi-bridge have been designed, respectively. Impacts of varied positional modifications are systematically studied. By utilizing PBDB-T as the donor, polymer solar cells are constructed with these two molecules as acceptors. Power conversion efficiencies of 11.09 and 9.46% are acquired for IDT-ToFIC- and IDT-TiFIC-based devices, respectively. Our studies have demonstrated that the use of thiophene spacers carrying one conjugated side chain at different positions can markedly enhance the photovoltaic properties relative to the corresponding control molecule IDTT2F.