Green-Solvent-Processed All-Polymer Solar Cells with Enhanced Efficiency and Stability through Molecular Design and Side-Chain Engineering.

Green-solvent-processed all-polymer solar cells (AP-SCs) are regarded as an excellent candidate for renewable energy due to their better stability and eco-friendly features. Two polymers, PYF-U and PYF-BO, have been designed by introducing a Y-series derivative with difluoro-substituted dicyanindenone units and a difluorobenzotriazole derivative as the first and second electron-deficient (A) units, respectively. The introduction of two additional F atoms on dicyanindenone units leads to a more coplanar backbone because of noncovalent interactions. Compared with the polymer PYF-U with undecyl chains on thiophene, the polymer PYF-BO with 2-butyloctyl chains exhibits stronger intermolecular aggregation during the film-forming process, more dominant face-on molecular packing, and higher crystallinity in films. Therefore, the PM6:PYF-BO AP-SC achieves an efficiency of 15.38%, outperforming that of the PM6:PYF-U device (14.27%). Moreover, the former exhibits a longer T80 lifetime (1789 h) than the latter (826 h) under thermal aging at 65 °C because of better molecular packing and morphology. Our research demonstrates that combining noncovalent interactions to enhance the coplanarity of the polymeric backbone with side-chain engineering to optimize molecular packing and blend-film morphology is one of the efficient strategies for developing high-performance polymer acceptors.