Asymmetric simple unfused acceptor enabling over 12% efficiency organic solar cells

High photovoltaic performance with cost-effective material synthesis and device fabrication are the prerequisite for commercialization of organic solar cells (OSCs). Herein, we conduct a systematic structure–property correlation study on unfused acceptors adopting different frameworks. Dithieno[3,2-b:2′,3′-d]pyrrole (DTP) based A-D1-D-D2-A asymmetric acceptor (DBT-4F) has been screened as a promising acceptor for high-efficient OSCs. Three DTP-based unfused acceptors display strong near-infrared absorption with narrow optical band gap (Egopt < 1.45 eV). Blends of DBT-4F with PBDB-T contribute a champion power conversion efficiency (PCE) of 12.14% due to better miscibility to form homogenous fibrous phase separation. To the best of our knowledge, the PCE is among the highest values for unfused acceptor based binary OSCs in the literature. The excellent performance of DBT-4F is revealed with more efficient photon-harvesting, higher and more balanced charge transport, and less charge recombination in the blends. Our work manifests the great potential of DTP based asymmetric unfused acceptor for developing high-efficient OSCs via rational molecular design.