Fluorinated End Group Enables High‐Performance All‐Polymer Solar Cells with Near‐Infrared Absorption and Enhanced Device Efficiency over 14

Fluorination of end groups has been a great success in developing efficient small molecule acceptors. However, this strategy has not been applied to the development of polymer acceptors. Here, a dihalogenated end group modified by fluorine and bromine atoms simultaneously, namely IC‐FBr, is first developed, then employed to construct a new polymer acceptor (named PYF‐T) for all‐polymer solar cells (all‐PSCs). In comparison with its non‐fluorinated counterpart (PY‐T), PYF‐T exhibits stronger and red‐shifted absorption spectra, stronger molecular packing and higher electron mobility. Meanwhile, the fluorination on the end groups down‐shifts the energy levels of PYF‐T, which matches better with the donor polymer PM6, leading to efficient charge transfer and small voltage loss. As a result, an all‐PSC based on PM6:PYF‐T yields a higher power conversion efficiency (PCE) of 14.1% than that of PM6:PY‐T (11.1%), which is among the highest values for all‐PSCs reported to date. This work demonstrates the effectiveness of fluorination of end‐groups in designing high‐performance polymer acceptors, which paves the way toward developing more efficient and stable all‐PSCs. A narrow bandgap polymer acceptor PYF‐T with fluorinated end groups on monomer sub‐units is synthesized, showing stronger and red‐shifted absorption, lower‐lying frontier molecular orbitals, higher electron mobility, enhanced intermolecular packing, and without sacrificing photovoltage compared to its non‐fluorinated counterpart (PY‐T). When employed in all‐polymer solar cells, PYF‐T yields an outstanding efficiency of 14.10%.