A Versatile and Low‐Cost Polymer Donor Based on 4‐Chlorothiazole for Highly Efficient Polymer Solar Cells

Benefiting from the emergence of narrow-band-gap small-molecule acceptors (SMAs), especially "Y" series, the power conversion efficiency (PCE) of polymer solar cells (PSCs) is rapidly improved. However, polymer donors with high efficiency, easy synthesis, and good universality are relatively scarce except PBDB-TF and D18. Herein, two polymer donors are designed and synthesized based on 4-chlorothiazole derivatives with simple structures, namely PTz3Cl and PBTTz3Cl. The OSCs based on PBTTz3Cl with slightly weaker intermolecular forces in comparison to PTz3Cl exhibits a decent PCE of 18.38% in blending with SMA L8-BO, owing to its strong donor/acceptor interaction with L8-BO, which shapes suitable phase separation morphology. Further research finds that PBTTz3Cl can exhibit excellent photovoltaic performances with various SMA materials, highlighting its universality. Based on this, ternary PSCs are designed where BTP-eC9 is introduced as a guest into the PBTTz3Cl:L8-BO host system. Thanks to further optimal blend morphology and more balanced charge transport, the PCE is improved up to 19.12%, which is among the highest values for PSCs. This work provides a new design of low-cost electron-deficient units for constructing highly versatile, high-performance polymer donors.