A series of soluble donor-acceptor conjugated polymers comprising of phenothiazine donor and various benzodiazole acceptors (i.e., benzothiadiazole, benzoselenodiazole, and benzoxadiazole) sandwiched between hexyl-thiophene linkers were designed, synthesized, and used for the fabrication of polymer solar cells (PSC). The effects of the benzodiazole acceptors on the thermal, optical, electrochemical, and photovoltaic properties of these low-bandgap (LBG) polymers were investigated. These LBG polymers possessed large molecular weight (M n ) in the range of 3.85À5.13 Â 10 4 with high thermal decomposition temperatures, which demonstrated broad absorption in the region of 300À750 nm with optical bandgaps of 1.80À1.93 eV. Both the HOMO energy level (À5.38 to À5.47 eV) and LUMO energy level (À3.47 to À3.60 eV) of the LBG polymers were within the desirable range of ideal energy level. Under 100 mW/cm 2 of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of electron donor polymers mixed with electron acceptor [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) or [6,6]-phenyl-C 71butyric acid methyl ester (PC 71 BM) in different weight ratios were investigated. The best performance of the PSC device was obtained by using polymer PP6DHTBT as an electron donor and PC 71 BM as an acceptor in the weight ratio of 1:4, and a power conversion efficiency value of 1.20%, an open-circuit voltage (V oc ) value of 0.75 V, a short-circuit current (J sc ) value of 4.60 mA/cm 2 , and a fill factor (FF) value of 35.0% were achieved. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [4823][4824][4825][4826][4827][4828][4829][4830][4831][4832][4833][4834] 2010
A series of novel low-bandgap triphenylaminebased conjugated polymers (PCAZCN, PPTZCN, and PDTPCN) consisting of different electron-rich donor main chains (N-alkyl-2,7-carbazole, phenothiazine, and cyclopentadithinopyrol, respectively) as well as cyano-and dicyano-vinyl electronacceptor pendants were synthesized and developed for polymer solar cell applications. The polymers covered broad absorption spectra of 400-800 nm with narrow optical bandgaps ranging 1.66-1.72 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the polymers measured by cyclic voltammetry were found in the range of À5.12 to À5.32 V and À3.45 to À3.55 eV, respectively. Under 100 mW/cm 2 of AM 1.5 white-light illumination, bulk heterojunction photovoltaic devices composing of an active layer of electron-donor polymers (PCAZCN, PPTZCN, and PDTPCN) blended with electron-acceptor [6,6]-phenyl-C 61 -butyric acid methyl ester or [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) in different weight ratios were investigated. The photovoltaic device containing donor PCAZCN and acceptor PC 71 BM in 1:2 weight ratio showed the highest power conversion efficiency of 1.28%, with V oc ¼ 0.81 V, J sc ¼ 4.93 mA/cm 2 , and fill factor ¼ 32.1%. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5812-5823, 2010
A series of low-band-gap (LBG) donor-accepor conjugated main-chain copolymers (P1-P4) containing planar 2,7carbazole as electron donors and bithiazole units (4,4 0 -dihexyl-2,2 0 -bithiazole and 4,4 0 -dihexyl-5,5 0 -di(thiophen-2-yl)-2,2 0 -bithiazole) as electron acceptors were synthesized and studied for the applications in bulk heterojunction (BHJ) solar cells. The effects of electron deficient bithiazole units on the thermal, optical, electrochemical, and photovoltaic (PV) properties of these LBG copolymers were investigated. Absorption spectra revealed that polymers P1-P4 exhibited broad absorption bands in UV and visible regions from 300 to 600 nm with optical band gaps in the range of 1.93-1.99 eV, which overlapped with the major region of the solar emission spectrum. Moreover, carbazole-based polymers P1-P4 showed low values of the highest occupied molecular orbital (HOMO) levels, which provided good air stability and high open circuit voltages (V oc ) in the PV applications. The BHJ PV devices were fabricated using polymers P1-P4 as electron donors and (6,6)-phenyl-C 61butyric acid methyl ester (PC 61 BM) or (6,6)-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) as electron acceptors in different weight ratios. The PV device bearing an active layer of polymer blend P4:PC 71 BM (1:1.5 w/w) showed the best power conversion efficiency value of 1.01% with a short circuit current density (J sc ) of 4.83 mA/cm 2 , a fill factor (FF) of 35%, and V oc ¼ 0.60 V under 100 mW/cm 2 of AM 1.5 white-light illumination.
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