Strengthening Near-Infrared Photon Harvesting in Semi-Transparent All-Polymer Solar Cells through the Synergy of Fluorination on the Selenide Monomer Backbone

All-polymer solar cells (all-PSCs) offer promising potential for large-scale manufacturing due to their remarkable mechanical and thermal stability. However, the limited capacity of polymer acceptors for near-infrared (NIR) photon harvesting has impeded their progress in semi-transparent (ST) all-PSCs. Here, the study develops a pair of new NIR polymer acceptors, named PYSeF-T and PYSe2F-T, with mono-/di-fluorinated end groups capped to the selenide monomer backbone, respectively. Owing to the stronger intermolecular interaction and intramolecular charge transfer effect of the di-fluorinated end groups with the selenide backbone, PYSe2F-T exhibits a stronger crystallinity and a more bathochromic absorption to 1000 nm. When blended with the donor, PM6, the PY2SeF-T-based all-PSC demonstrates a higher efficiency of 16.73% with a remarkable short-circuit current (JSC) of 27.7 mA cm-2, which is the highest JSC for all-PSCs. Based on these, the ST device based on PM6:PYSe2F-T demonstrates a superior efficiency of 12.52% with an average visible transmittance of 26.2% and a light utilization efficiency of 3.28%, outperforming the mono-fluorinated counterpart. The work provides an in-depth understanding of the above synergistic effects to develop NIR polymer acceptors and establishes a solid foundation for future investigations into large-area and flexible ST all-PSCs. The synergy of fluorination on the selenide monomer enables a novel polymer acceptor (PYSe2F-T) with a bathochromic absorption onset (approximate to 1000 nm) and ordered packing. PYSe2F-T-based devices yield an impressive short-circuit current density of 27.7 mA cm-2 with a higher efficiency of 16.7%. Beneficial from its near-infrared response, PYSe2F-T can also provide a decent performance of 12.6% in semitransparent devices with an average visible transmittance of 26.2%. image