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High-Efficiency All-Polymer Solar Cells with Poly-Small-Molecule Acceptors Having π‑Extended Units with Broad Near-IR Absorption

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journal contribution
posted on 29.01.2021, 16:07 by Ning Su, Ruijie Ma, Guoping Li, Tao Liu, Liang-Wen Feng, Chenjian Lin, Jianhua Chen, Jun Song, Yiqun Xiao, Junle Qu, Xinhui Lu, Vinod K. Sangwan, Mark C. Hersam, He Yan, Antonio Facchetti, Tobin J. Marks
We report two new poly-small-molecule acceptors, PYN-BDT and PYN-BDTF, which serve, by virtue of their π-extended naphthalene rings, as broad optical cross-section macromolecular absorbers (extending to ∼900 nm; ΔEopticalgap = 1.38 eV) in all-polymer solar cells (APSCs). APSCs fabricated by blending PYN-BDT or PYN-BDTF with PM6 exhibit power conversion efficiencies (PCEs) of 7.24 and 9.08%, respectively, while blends with PBDB-T exhibits far higher PCEs of 12.06 and 13.22%, respectively; the latter cell achieves Jsc = 22.28 mA cm–2, among the highest known for an APSC. The results of blend morphology, GIWAXS, charge transport, exciton and carrier dynamics, PL quenching efficiency, and impedance-based analysis indicate that the PBDB-TT:PYN-BDTF blends and their APSCs outperform the corresponding PM6:PYN-BDTF devices due to significantly suppressed bimolecular recombination. These results demonstrate that π-conjugative extension of individual polymer acceptor blocks represents an efficient strategy to broaden APSC optical cross sections, decrease bimolecular recombination, and achieve high-performance cells with enhanced Jsc metrics.