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Low-Bandgap n‑Type Polymer Based on a Fused-DAD-Type Heptacyclic Ring for All-Polymer Solar Cell Application with a Power Conversion Efficiency of 10.7%

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journal contribution
posted on 29.04.2020 by Ailing Tang, Jianfeng Li, Bao Zhang, Jing Peng, Erjun Zhou
An n-type polymer (A701) is designed and synthesized with an alternative A′–DAD–A′-D′ backbone, where 1,1-dicyanomethylene-3-indanone (IC), dithienothiophen­[3,2-b]-pyrrolobenzothiadiazole (TPBT), and benzodithiophene (BDT) are used as A′, DAD, and D′ units, respectively. A701 shows enhanced light absorption with a narrow bandgap of 1.42 eV and a high absorption coefficient of 6.85 × 104 cm–1 at 780 nm. It displays an uplifted LUMO (the lowest unoccupied molecular orbital) level of −3.80 eV. By introducing a high point solvent additive of 1,8-diiodooctane (DIO), all-polymer solar cells (all-PSCs) based on the PBDB-T:A701 blend exhibit efficient exciton dissociation, enhanced charge transport, and decreased bimolecular recombination. Thus, a high open-circuit voltage (VOC) of 0.92 V, a short-circuit current (JSC) of 18.27 mA cm–2, and a fill factor (FF) of 0.64 are attained, affording an impressive power conversion efficiency (PCE) of 10.70%. The low voltage loss of 0.50 V and high efficiency of 10.7% are among the top values for all-PSCs. Our results indicate that the fused DAD-type heptacyclic ring can be utilized to construct not only nonfullerene small molecular acceptors but also promising polymer acceptors.