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Two donor–acceptor (D–A) backbone copolymers with different fused ring acceptors, i.e., dithieno [2,3‐e:3′,2′‐g]isoindole‐7,9(8 H)‐dione (DTID) and dithieno[3′,2′:5,6;2″,3″:7,8]naphtho[2,3‐d]imidazol‐9(10 H)‐one (DTNID) and same benzo[1,2‐b:4,5‐b′]dithiophene with alkylated aromatic side as side chains (BDTT) donor, denoted as P133 and P135 are synthesized and used as donor along with narrow bandgap nonfullerene Y6 acceptor for the preparation of polymer solar cells (PSCs). The dielectric constant of P135:Y6 is higher than that of P133:Y6 due to the strong electron deficient ability of DTNID compared to DTID, which fostered exciton dissociation and charge transport, constrained charge recombination, and ultimately boosted the power conversion efficiency of P135:Y6 to 15.11%, which is higher than P133:Y6 (10.24%). Therefore, these investigations confirm the pronounced potential of fused ring DTNID as an acceptor unit for emerging D–A copolymers for PSCs with high efficiency. [ABSTRACT FROM AUTHOR]

Three D--A conjugated copolymers based on the same 8,10-dihydro-9Hbisthieno[ 2 0,3 0:7.8;3 00,2 00:5.6]naphtho[2,3-d]imidazol-9-one (DTNIA) acceptor unit and different donor units, i.e., 2-dodecylbenzo[1,2-b:3,4-b 0:6,5-b 00]trithiophene (3TB) (P1), 5,6-dioctylnaphtho[2,1-b:3,4-b 0]dithiophene (DTN) (P2), and 4,5-diundecylbenzo[2,1-b:3,4-b 0]dithiophene (DTB) (P3), are formulated and synthesized. All the copolymers exhibit deep highest occupied molecular energy levels of -5.43, -5.50, and -5.51 eV for P1, P2, and P3, respectively, and show an optical bandgap of 2.18, 2.12, and 2.11 eV, for P1, P2, and P3, respectively. These copolymers are used as donors for the construction of polymer solar cells combining ITIC-m as an electron acceptor. The optimized polymer solar cells based on P1:ITIC-m, P2:ITIC-m, and P3:ITIC-m realize overall power conversion efficiency of ≈9.62%, 12.84%, and 11.80%, respectively. The greater value of open circuit voltage for P2 and P3 relative to P1 may be due to the deeper highest occupied molecular orbital energy level of P2 and P3 as compared to P1. The highest power conversion efficiency for the P2-based polymer solar cells may be originated from the denser π--π stacking distance and relatively improved crystallinity, which are advantageous for balanced charge transport, resulting in a comparatively high fill factor and short circuit current. [ABSTRACT FROM AUTHOR]

A series of novel donor–acceptor (D–A) random conjugated terpolymers P2‐P4 along with the homopolymers P1 (BDT‐DPP) and P5 (BDT‐BTDQ) were designed and synthesized by copolymerizing a benzo[1,2‐b:4,5‐b]dithiophene (BDT) donor with an electron‐deficient diketopyrrolo[3,4‐c]pyrrole (DPP) unit and a benzothiadiazolo[3,4‐e]quinoxaline (BTDQ) moieties of different electron‐withdrawing strengths, and the resultant terpolymers showed broad absorption profile ranging from 300 to 1200 nm. The HOMO levels of the polymers were adjusted from −5.23 to −5.11 eV, and the optical bandgaps were controlled from 1.32 to 1.13 eV by changing the molar ratio of DPP and BTDQ acceptors. These terpolymers were used as a donor along with PC71BM as an acceptor for the creation of polymer solar cells, and the performance was optimized via variable the donor to acceptor ratio and solvent vapor annealing. The polymer solar cells made from the random terpolymer P3 showed the highest overall power conversion efficiency of (9.27%), which is higher than that for the corresponding homo‐polymers counterparts, that is, P1 (7.27%) and P5 (7.68%). The results demonstrate that the designing of random D‐A1‐D‐A2 terpolymers may be the best approach for efficient polymer solar cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1478–1485 [ABSTRACT FROM AUTHOR]