End-Extended Conjugation Strategy to Reduce the Efficiency-Stability-Mechanical Robustness Gap in Binary All-Polymer Solar Cells.

Concurrently achieving high efficiency, mechanical robustness and thermal stability is critical for the commercialization of all-polymer solar cells (APSCs). However, APSCs usually demonstrate complicated morphology, primarily attributed to the polymer chain entanglement which has a detrimental effect on their fill factors (FF) and morphology stability. To address these concerns, an end-group extended polymer acceptor, PY-NFT, was synthesized and studied. The morphology analysis showed a tightly ordered molecular packing mode and a favorable phase separation was formed. The PM6 : PY-NFT-based device achieved an exceptional PCE of 19.12 % (certified as 18.45 %), outperforming the control PM6 : PY-FT devices (17.14 %). This significant improvement highlights the record-high PCE for binary APSCs. The thermal aging study revealed that the PM6 : PY-NFT blend exhibited excellent morphological stability, thereby achieving superior device stability, retaining 90 % of initial efficiency after enduring thermal stress (65 °C) for 1500 hours. More importantly, the PM6 : PY-NFT blend film exhibited outstanding mechanical ductility with a crack onset strain of 24.1 %. Overall, rational chemical structure innovation, especially the conjugation extension strategy to trigger appropriate phase separation and stable morphology, is the key to achieving high efficiency, improved thermal stability and robust mechanical stability of APSCs.