Near-infrared Absorbing Polymer Acceptors Enabled by Selenophene-fused Core and Halogenated End-group for Binary all-polymer Solar Cells With Efficiency Over 16%

Abstract Due to the vigorous development of polymerized small-molecule acceptors (PSMAs), all-polymer solar cells (all-PSCs) have made tremendous advancement recently. However, their power conversion efficiencies (PCEs) are still restricted by the lack of PSMAs with desirable optoelectronic properties, especially the ability to capture the near-infrared photons. To resolve this, two near-infrared absorbing PSMAs, namely PY2Se-F and PY2Se-Cl, with a selenophene-fused core and halogenated end-group are developed. Combining the synergistic effects of selenium and fluorine (F)/chlorine (Cl) substitutions in broadening absorption and enhancing intermolecular interactions, PY2Se-F and PY2Se-Cl show significantly red-shifted absorption (30-40 nm) and reasonably deep-shifted lowest unoccupied molecular orbital (LUMO) levels compared with the pristine PY2S-H and fluorinated PY2S-F. When replacing F with Cl on the end-group, the PY2Se-Cl shows a better blend morphology with polymer donor PM6, compared with the PY2Se-F-based one, leading to better charge transport. As a result, the PM6:PY2Se-Cl-based all-PSCs achieve an impressive PCE of 16.1% with both high short-circuit current density (Jsc) of 24.5 mA cm-2 and fill factor (FF) of 0.743, which are among the highest values in the reported binary all-PSCs so far. Notably, this is the first example of chlorinated end-group derived PSMAs. Combining with the low-cost merit of chlorination, PY2Se-Cl shows great potential in the practical applications of efficient all-PSCs.