Medium bandgap A-DA’D-A type small molecule acceptors prepared by synergetic modification strategy for efficient indoor organic photovoltaic devices

Organic photovoltaic (OPV) is one of the most promising technologies for powering indoor electronic devices. The high-performance indoor organic photovoltaics (IOPV) require medium bandgap materials to absorb visible light efficiently and reduce energy loss. However, state-of-the-art A-DA’D-A type small molecule acceptors (SMAs) have absorptions in the near-infrared region which mismatches with the room light. In this work, two medium bandgap A-DA’D-A type SMAs BTOL-Br and DFOL-Br were synthesized by a molecular synergetic modification strategy for the applications in IOPV. Our results show that DFOL-Br with replacing the A’ unit of benzothiadiazole in BTOL-Br by difluorine substituted benzene ring, exhibits blue-shifted absorption spectra and an up-shifted lowest unoccupied molecular orbital (LUMO) energy level than those of BTOL-Br. When blending the SMAs with a polymer donor PBQx-TCl, the DFOL-Br-based film shows more ordered molecular packing and suitable phase separation. As a result, the DFOL-Br-based device achieves a higher indoor efficiency of 26.8% under a 2600 K light-emitting diode lamp at 2000 lux than that of the BTOL-Br-based one (23.2%). This work indicates that the synergetic modification is an effective strategy for preparing medium bandgap A-DA’D-A type SMAs, which may become a useful SMA design guideline for developing high-performance IOPVs.