Electronic Properties and Photovoltaic Performances of a Series of Oligothiophene Copolymers Incorporating Both Thieno[3,2- b ]thiophene and 2,1,3-Benzothiadiazole Moieties (original) (raw)
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Journal of Photochemistry and Photobiology A: Chemistry, 2013
After the discovery of photoinduced charge transfer in conjugated polymers, organic photovoltaic solar cells have been extensively studied due to many advantages that include flexibility and low-cost. In this context, we have synthesized a new class of conjugated polymer, poly(2-(4-{1-cyano-2-[5-(3-thiophen-2-yl-benzo[c]thiophen-1-yl)-thiophen-2-yl]-vinyl}-2,5bis-hexyloxy-phenyl)-but-2-enenitrile) (CN-PTBTBPB) for the fabrication of low cost organic solar cells. The electron donor properties of CN-PTBTBPB polymer was incorporated by means of facile Knoevenagel condensation process followed by a chemical oxidative polymerization method using oligo-5-(1-benzo[c]thiophen-3-yl)thiophene-2-carboxaldehyde with 1,4-bis(cyanomethyl) benzene linkages. The polymer was characterized by 1 H NMR and GPC techniques. The electronic and structural properties of the polymer were evaluated by UV-vis spectroscopy, fluorescence spectroscopy, and thermo gravimetric analysis. In order to establish the energy diagram of the prepared polymer, the energy gap between HOMO-LUMO was evaluated using electrochemical measurements and Density Functional Theory (DFT). The resulting CN-PTBTBPB polymer was experimentally found to possess low-lying HOMO (about −5.84 eV) and high-lying LUMO (about −3.87 eV) energy levels. This polymer exhibited a relatively wide optical band gap of ∼1.95 eV in the solid state. Using this polymer, organic photovoltaic cells were fabricated in open air of type ITO/PEDOT:PSS/CN-PTBTBPB:PCBM/Al showed promising photovoltaic properties.
RSC Adv., 2014
We report a comparative study on four donor-acceptor benzothiadiazole-based copolymers containing dithienyl or thienothiophene moieties for application in organic photovoltaic (OPV) devices. Bulkheterojunction OPV devices are fabricated having power conversion efficiencies ranging between 4 and 6%. Morphological, spectroscopic and charge-transport measurements are used to investigate the influence of either the dithienyl or thienothiophene moieties on the structure and photophysical properties of the copolymer and copolymer:PC 71 BM blend films and rationalise the solar cell characteristics. Although all copolymer:PC 71 BM blends exhibit comparable hole polaron yields, solar cell devices with the highest power conversion efficiencies are correlated with increased charge-carrier mobility of the copolymer and enhanced aggregation of PC 71 BM in the blend. † Electronic supplementary information (ESI) available: OPV device optimisation data, GIWAXS measurements of pure polymer lms, AFM scans of blend lm surface, PL spectra of neat and blend thin-lms and OFET transfer and output characteristics. See
Synthetic Metals, 2013
Full donor-type conjugated polymers containing benzodithiophene and thiophene derivative units were synthesized as electron donors for organic photovoltaic devices. The alkoxy-substituted benzo[1,2b:4,5-b ]dithiophene (BDT) monomer, 2,6-bis(trimethyltin)-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:4,5b ]dithiophene, was polymerized with 2,5-dibromothiophene through a Pd(0)-catalyzed Stille coupling reaction. To enhance the interchain interactions between polymers chains, an alkylselenophenesubstituted BDT derivative was newly synthesized, and copolymerized with the same counter monomer parts. The two newly synthesized polymers were characterized for use in organic photovoltaic devices as electron donors. Measured optical band gap energies of the polymers were 2.10 and 1.96 eV, depending on polymer structure. Field-effect transistors were fabricated using the polymers to measure their hole mobilities, which ranged from 10 −3 to 10 −5 cm 2 V −1 s −1 depending on the polymer structure. Bulk heterojunction organic photovoltaic cells were fabricated using conjugated polymers as electron donors and a [6,6]-phenyl C 71-butyric acid methyl ester (PC 71 BM) as an electron acceptor. One fabricated device showed a power conversion efficiency of 2.73%, an open-circuit voltage of 0.72 V, a short-circuit current of 7.73 mA cm −2 , and a fill factor of 0.46, under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm −2).
Current Applied Physics, 2015
Three kinds of donor-acceptor (D-A) type photovoltaic polymers were synthesized based on 2,7carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be-5.72,-5.67 and-5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C 71 butyric acid methyl ester (PC 71 BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (V OC) in the range, 0.86~0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high V OC , the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (J SC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC 71 BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron-hole recombination at the polymer/PC 71 BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC 71 BM. The PCBTTPD:PC 71 BM device showed the best PCE of 3.42% with a V OC and J SC of 0.86 V and 7.79 mA cm-2 , respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high V OC and sufficient energy offset for ensuring efficient hole transfer from PC 71 BM to the polymer.
Polymer Chemistry, 2014
A new benzo[1,2-b:4,5-b']dithiophene (BDT) building block with 4,8-disubstitution using 2-(2ethylhexyl)-3-hexylthieno[3,2-b]thiophene as the substituent has been designed and synthesized. The new building block has been copolymerized with benzothiadiazole (BT) and 5,6-difluorobenzothiadiazole (fBT) by Suzuki and Stille coupling polymerization to synthesize donor-acceptor conjugated polymers. The optical and electrochemical properties of the synthesized copolymers were studied. Bulk heterojunction solar cells were fabricated using the donor-acceptor copolymers in conjunction with PC 71 BM and exhibited up to 4.20% power conversion efficiency. 65 the delocalization of holes over the side chain, thus lowering
Journal of Applied Polymer Science, 2012
Two conjugated copolymers, poly{4,7-[5,6bis(octyloxy)]benzo(c)(1,2,5)thiadiazole-alt-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:3,4-b]dithiophene} (P1) and poly(2-{5-[5,6bis(octyloxy)-4-(thiophen-2-yl)benzo(c)(1,2,5)thiadiazol-7-yl] thiophen-2-yl}-4,8-di(2-ethylhexyloxyl)benzo(1,2-b:3,4-b)dithiophene) (P2), composed of benzodithiophene and 5,6-dioctyloxybenzothiadiazole derivatives with or without thiophene units were synthesized via a Stille cross-coupling polymerization reaction. These copolymers are promising for applications in bulk heterojunction solar cells because of their good solubility, proper thermal stability, moderate hole mobility, and low band gap. The photovoltaic proper-ties of these copolymers were investigated on the basis of blends of the different polymer/(6,6)-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) weight ratios under AM1.5G illumination at 100 mW/cm 2 . The device with indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/P2:PC 71 BM (1 : 2 w/w)/Ca/Al gave a relatively better photovoltaic performance with a power conversion efficiency of 1.55%. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: 3936-3945, 2012
Journal of Polymer Science Part A: Polymer Chemistry, 2012
It has been shown recently, that the presence of alkyl side chains at the 3-positions on the thiophene rings placed next to 2,1,3-benzothiadiazole core in the backbone of several conjugated polymers results in severe steric hindrance and prevents efficient planarity of the thiophene-2,1,3-benzothiadiazole-thiophene (TBzT) segment. Both properties have a strong influence on the optoelectronic properties of the polymer and need to be considered when the polymer is to be used for organic electronics applications. In this work, we modified a previously synthesized oligothiophene copolymer, consisting of two 3,4 0-dialkyl-2,2 0bithiophene units attached to a 2,1,3-benzothiadiazole unit (TBzT segment) and a thieno[3,2-b]thiophene unit, by optimizing the lateral alkyl side chains following a density functional theory investigation. It is demonstrated that eliminating the alkyl side chains from the 3-positions of the TBzT segment and anchoring them onto the thieno[3,2-b]thiophene, using an efficient synthesis of the 3,6-dihexylthieno[3,2-b]thiophene unit, allows us to reduce the energy band gap. In addition, the chemical modification leads to a better charge transport and to an enhanced photovoltaic efficiency of polymer/fullerene blends. V