A Medium‐Bandgap Nonfullerene Acceptor Enabling Organic Photovoltaic Cells with 30% Efficiency under Indoor Artificial Light

Abstract The correlation between molecular structure and photovoltaic performance is lagging for constructing high‐performance indoor organic photovoltaic (OPV) cells. Herein, this relationship is investigated in depth by employing two medium‐bandgap nonfullerene acceptors (NFAs). The newly synthesized NFA of FTCCBr exhibits a similar bandgap and molecular energy level, but a much stronger dipole moment and larger average electrostatic potential (ESP) compared with ITCC. After blending with the polymer donor PB2, the PB2:ITCC and PB2:FTCCBr blends exhibit favorable bulk‐heterojunction morphologies and the same driving force, but the PB2:FTCCBr blend exhibits a large ESP difference. In OPV cells, the PB2:ITCC‐based device produces a power conversion efficiency (PCE) of 11.0%, whereas the PB2:FTCCBr‐based device gives an excellent PCE of 14.8% with an open‐circuit voltage (V_OC) of 1.05 V, which is the highest value among OPV cells with V_OC values above 1.0 V. When both acceptor‐based devices work under a 1000 lux of 3000 K light‐emitting diode, the PB2:ITCC‐based 1 cm² device yields a good PCE of 25.4%; in contrast, the PB2:FTCCBr‐based 1 cm² device outputs a record PCE of 30.2%. These results suggest that a large ESP offset in photovoltaic materials is important for achieving high‐performance OPV cells.