Over 14% Efficiency in Polymer Solar Cells Enabled by a Chlorinated Polymer Donor

Fluorine‐contained polymers, which have been widely used in highly efficient polymer solar cells (PSCs), are rather costly due to their complicated synthesis and low yields in the preparation of components. Here, the feasibility of replacing the critical fluorine substituents in high‐performance photovoltaic polymer donors with chlorine is demonstrated, and two polymeric donors, PBDB‐T‐2F and PBDB‐T‐2Cl, are synthesized and compared in parallel. The synthesis of PBDB‐T‐2Cl is much simpler than that of PBDB‐T‐2F. The two polymers have very similar optoelectronic and morphological properties, except the chlorinated polymer possess lower molecular energy levels than the fluorinated one. As a result, the PBDB‐T‐2Cl‐based PSCs exhibit higher open circuit voltage (Voc) than the PBDB‐T‐2F‐based devices, leading to an outstanding power conversion efficiency of over 14%. This work establishes a more economical design paradigm of replacing fluorine with chlorine for preparing highly efficient polymer donors. A chlorinated polymer donor, PBDB‐T‐2Cl, is synthesized and compared in parallel with its fluorinated counterpart, PBDB‐T‐2F. PBDB‐T‐2Cl exhibits a much simpler synthesis route, which is favorable for future practical application of organic solar cells; in addition, a high power conversion efficiency of 14.4% (with certified PCE of 13.9% by the National Institute of Metrology) and good stability tested over 1000 h is achieved.