Regio‐Regular Polymer Acceptors Enabled by Determined Fluorination on End Groups for All‐Polymer Solar Cells with 15.2% Efficiency

Polymerization sites of small molecule acceptors (SMAs) plays a vital role in determining device performance of all-polymer solar cells (all-PSCs). Different from our recent work about fluoro- and bromo- co-modified end group of IC-FBr (a mixture of IC-FBr1 and IC-FBr2), in this paper, we synthesized and purified two regiospecific fluoro- and bromo- substituted end groups (IC-FBr- o & IC-FBr- m ), which were then employed to construct two regio-regular polymer acceptors named PYF-T- o and PYF-T- m respectively. In comparison with its isomeric counterparts named PYF-T- m with different conjugated coupling sites, PYF-T- o exhibits stronger and bathochromic absorption to achieve better photon harvesting. Meanwhile, PYF-T- o adopts more ordered inter-chain packing and suitable phase separation after blending with the donor polymer PM6, which resulted in suppressed charge recombination and efficient charge transport. Strikingly, we observed a dramatic performance difference between the two isomeric polymer acceptors PYF-T- o and PYF-T- m . While devices based on PM6:PYF-T- o can yield power conversion efficiency (PCE) of 15.2%, devices based on PM6:PYF-T- m only show poor efficiencies of 1.4%. This work demonstrates the success of configuration-unique fluorinated end groups in designing high-performance regular polymer acceptors, which provides guidelines towards developing all-PSCs with better efficiencies.