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Donor-acceptor(D-A)-conjugated polymers P(BT-C1)and P(BT-C2),with dithieno[2,3-b;7,6-b]carbazole(C1)or dithieno[3,2-b;6,7-b]carbazole(C2)as D-unit and benzothiadiazole(BT)as A-unit,were synthesized.The optical bandgaps of the polymers are similar(1.84 and 1.88 e V,respectively).The structures of donor units noticeably influence the energy levels and backbone curvature of the polymers.P(BT-C1)shows a large backbone curvature;its highest occupied molecular orbital(HOMO)energy level is 5.18 e V,whereas P(BT-C2)displays a pseudo-straight backbone and has a HOMO energy level of 5.37 e V.The hole mobilities of the polymers without thermal annealing are 1.9×10 3 and 2.7×10 3 cm2 V 1 s 1 for P(BT-C1)and P(BT-C2),respectively,as measured by organic thin-film transistors(OTFTs).Polymer solar cells using P(BT-C1)and P(BT-C2)as the donor and phenyl-C71-butyric acid methyl ester(PC71BM)as the acceptor were fabricated.Power conversion efficiencies(PCEs)of 4.9%and 5.0%were achieved for P(BT-C1)and P(BT-C2),respectively.The devices based on P(BT-C2)exhibited a higher Voc due to the deeper HOMO level of the polymer,which led to a slightly higher PCE.
Conjugated polymers P (BT-C1) and P (BT-C2) with dithieno [2,3-b; 7,6-b] carbazole (C1) or dithieno [3,2-b ; 6,7-b] carbazole (C2) as D-unit and benzothiadiazole (BT) as A-unit, were synthesized.The optical bandgaps of the polymers are similar (1.84 and 1.88 eV, respectively) units noticeably affect the energy levels and backbone curvature of the polymers. P (BT-C1) shows a large backbone curvature; its highest percentage of molecular orbital (HOMO) energy levels is 5.18 eV, P -straight backbone and has a HOMO energy level of 5.37 eV. The hole mobilities of the polymers without thermal annealing are 1.9 × 10 3 and 2.7 × 10 3 cm 2 V 1 s 1 for P (BT-C1) and P (BT- C2), respectively, as measured by organic thin-film transistors (OTFTs). Polymer solar cells using P (BT-C1) and P (BT- C2) as the donor and phenyl- C71- butyric acid methyl ester (PC71BM) as the acceptor were fabricated. Power conversion efficiencies (PCEs) of 4.9% and 5.0% were achieved for P (BT-C1) and P (BT-C2), respectively. These devices based on P (BT-C2) exhibited a higher Voc due to the deeper HOMO level of the polymer, which led to a slightly higher PCE.