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To examine the effects of pendent alkyl chain on the benzodithiophenedione (BDD) acceptor in the donor–acceptor (D–A) conjugated copolymers, two D–A copolymers with same thiazole ring substituted benzo[1,2‐b:4,5‐b′]dithiophene (BDTTz) and different acceptors BDD with two pendent alkyl units PBDTTz‐BDD and one pendent alkyl unit in benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione (BDTD) PBDTTz‐BDTD are synthesized. There is small effect on the optical properties but significant effect on the intermolecular π–π stacking, charge transport, and photovoltaic performance. PBTTz‐BDTD (with one pendent alkyl chain) on the BDD exhibits smaller π–π stacking distance as compared to PBDTTz‐BDD (with two pendent alkyl chains). The balanced charge carrier mobilities for the PBDTTZ‐BDTD based blends than those for PBDTTz‐BDD based blends are beneficial for suppressing the recombination processes, resulting in higher short circuit current and fill factor for the polymer solar cells (PSCs) based on PBDTTz‐BDTD. Combined with BThIND or Y6 as acceptor, PBDTTZ‐BDTD based PSCs show power conversion efficiency of 12.85% and 14.08%, respectively, which are larger than that for PBDTTz‐BDD counterparts (10.46% and 10.90% for BThIND and Y6, respectively). Thus, the photovoltaic performance of the D–A copolymer donors can be regulated through the slight variations of the pendent alkyl chains in the BDD acceptor unit. [ABSTRACT FROM AUTHOR]

Two donor–acceptor (D‐A) copolymers, P128 and P129, containing benzodithiophene (BDT) and naphthiodithiophene (NDT) donor unit, respectively, and the alike anthra[1,2‐b:4,3,bʹ:6,7‐cʺ] trithiophene‐8‐12‐dione(A3T) as an acceptor unit, are synthesized. The P129 (NDT donor) exhibits enhanced chain planarity and linearity of backbone compared to P128 (BDT donor), which leads to a considerable increase in both the light‐harvesting ability and hole mobility. In addition to it, the incorporation of the NDT unit creates a strong modification in the morphology with a well‐mixed interpenetrating nanofibrillar network with an increased donor–acceptor interface in the P129:Y6 bulk heterojunction active layer that leads to a high short‐circuit current density and fill factor. The power conversion efficiency (PCE) of the improved polymer solar cells based on P128:Y6 and P129:Y6 is 6.25% and 14.55%, respectively. The negative HOMO offset (−0.02 eV) at P128/Y6 interface restricts the hole transfer from Y6 to P128 and results in low value of short‐circuit current and thereby poor PCE. Finally, the ternary PSCs are constructed with a weight ratio of 0.5:0.5 between P128 and P129 and the weight component of Y6 is kept constant and the PSC attains a PCE of 16.19%. This increase in the PCE can be attributed to the formation of semiconducting alloy based on P128 and P129 donors and the transformation of HOMO offset from negative (−0.02 eV for Y6/P128) to positive (0.04 eV for Y6/P128:P129). [ABSTRACT FROM AUTHOR]

Two D‐A copolymers consisting of fused ring pyrrolo‐dithieno‐quinoxaline acceptors are synthesized with different donor units, i.e., benzodithiophene (BDT) with alkylthienyl (P134) and 2‐ethylhexyloxy (P117) side chains. These copolymers are used as donors and a narrow bandgap acceptor Y6 to fabricate bulk heterojunction polymer solar cell devices. Owing to the strong electron‐deficient fused ring pyrrolo‐bithieno‐quinoxaline and weak alkyl thienyl side chains in BDT, the polymer solar cells (PSCs) based on P134:Y6 attain the power conversion efficiency (PCE) of 15.42%, which is higher than the P117:Y6 counterpart (12.14%). The superior value of PCE for P134:Y6 can be associated with more well‐adjusted charge transport, weak charge recombination, proficient exciton generation, and dissociation into free charge carriers and their subsequent charge collection owing to the dense π–π stacking distance and more considerable crystal coherence length for the P134:Y6 thin films. This investigation confirms the great potential of a strong acceptor‐weak donor tactic for developing efficient D‐A copolymers consists of quinoxaline acceptor for PSCs. [ABSTRACT FROM AUTHOR]

Two new wide bandgaps D−A copolymers compromising of same benzo [1,2‐b:4, 5‐b′]dithiophene functionalized with thiazole side‐chain donor unit and different acceptors units, i. e., fluorinated benzotriazole (FBTA) (PBDTTZ‐FBTA) and bis‐thiophene‐thieno‐benzothiazole (BTZ) (PBDTTZ‐BTZ) were synthesized and their optical and electrochemical properties were investigated. These copolymers exhibit appropriate frontier energy levels and complementary absorption to most middle and narrow bandgap non‐fullerene small molecule non‐fullerene acceptors. We have explored using these two copolymers as donors combined with a narrow bandgap non‐fullerene acceptor, namely BThIND−Cl, for the construction of polymer solar cells. The optimized polymer solar cells employing PBDTTZ‐FBTA: BThIND−Cl showed overall power conversion efficiency of 14.96 % (with energy loss of 0.51 eV), which is higher than that for PBDTTZ‐BTZ: BThIND−Cl (11.68 % with energy loss of 0.56 eV). Although the PBDTTZ‐BTZ exhibits a broader absorption profile than that of PBDTTZ‐FBTA, the higher power conversion efficiency of the later copolymer may be correlated with the high charge carrier mobility, suppression of the bimolecular and trap‐assisted recombination due to appropriate phase separation and compact π‐π stacking distance in the active layer and low energy loss. [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]

Developing efficient wide-bandgap copolymer donor materials to match with narrow bandgap non-fullerene acceptors is continuously ongoing for polymer solar cells. Herein, two new D-A copolymers are designed and synthesized by embedding the same anthra[1,2-b:4,3-b':6,7-c"] trithiophene-8,12-dione (A3T) acceptor unit and different donor units, i.e., BDTTZ (P126) and BDTTh (P127). These copolymers showed broad absorption from 350 to 680 nm and deeper HOMO energy level. We have used these two copolymers as donors and a narrow bandgap non-fullerene acceptor Y6 to prepare bulk heterojunction polymer solar cells (PSCs). After the optimization, P126 :Y6 and P127 :Y6 attained overall power conversion efficiency of 15.07% and 12.27%, respectively. The higher PCE for the P126 than P127 is associated with the more efficient photon harvesting and photogenerated excitons, balanced charge transport, and low energy loss. Our results may help to design new polymers with a deeper highest occupied molecular orbital level that will be well-matched with non-fullerene acceptors. [Display omitted] • We have used the approach of weak donor and strong acceptor approach to design the D-A copolymers. • Two D-A copolymers were designed with same A3T acceptor and different donors, i.e., BDTTZ (P126) and BDTTh (P127). • Both the copolymers showed deeper HOMO energy level to achieved high V OC. • P126 :Y6 and P127 :Y6 showed power conversion efficiency of 15.07% and 12.27%, respectively. [ABSTRACT FROM AUTHOR]