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- Admassie, Shimelis, et al.
(författare)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 156:7-8, s. 614-623
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical and optical properties of a series of alternating polyfluorene copolymers with low band gaps were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor-acceptor-donor (DAD) sequence to achieve the lowering of band gaps. The polymers were solvent-casted on platinum disk electrode and the band gaps were estimated from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochemically determined band gaps were found to be slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps determined range from 2.1 to 1.3 eV. © 2006 Elsevier B.V. All rights reserved.
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| 5. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Conjugated polymers with polar side chains in bulk heterojunction solar cell devices
- 2014
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Ingår i: Polymer International. - : Wiley. - 1097-0126 .- 0959-8103. ; 63:1, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- Two polymers with polar side chains, namely poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(5',8'-di-2-thienyl-(2',3'-bis(3''-(2-(2-methoxyethoxy)ethoxy)phenyl)quinoxaline))] (P1) and poly[2,7-(9,9-bis(2-(2-methoxyethoxy)ethyl)fluorene)-alt-5,5-(5',8'-di-2-thienyl-(2',3'-bis(3''-(2-(2-methoxyethoxy)-ethoxy)phenyl)quinoxaline))] (P2), were synthesized for solar cell application. A series of bulk heterojunction solar cells were systematically fabricated and characterized by varying the electron-acceptor materials, processing solvents and thickness of the active layer. The results show that P1, with a higher molecular weight and good film-forming properties, performed better. The best device showed an open circuit voltage of 0.87 V, a short circuit current of 6.81 mA cm(-2) and a power conversion efficiency of 2.74% with 1:4 polymer:[6,6]-phenyl-C71-butyric acid methyl ester (PCBM[70]) mixture using o-dichlorobenzene (o-DCB) as processing solvent. P2 on the other hand showed a poorer performance with chlorobenzene as processing solvent, but a much improved performance was obtained using o-DCB instead. Thus, an open circuit voltage of 0.80 V, short circuit current of 6.21 mA cm(-2) and an overall power conversion efficiency of 2.22% were recorded for a polymer:PCBM[70] mixing ratio of 1:4. This is presumably due to the improvement of the morphology of the active layer using o-DCB as processing solvent. (c) 2013 Society of Chemical Industry
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| 6. |
- Lindgren, Lars Johan, 1977, et al.
(författare)
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Synthesis, Characterization, and Devices of a Series of Alternating Copolymers for Solar Cells
- 2009
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Ingår i: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:15, s. 3491-3502
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report the synthesis, characterization. and photovoltaic properties of a series of six Conjugated polymers based on donor-acceptor-donor (DAD) structure. The polymers are obtained via Suzuki polymerization of different alkoxy-substituted DAD monomers together with a substituted fluorene or phenylene monomer. Application of polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with both [60]PCBM and [70]PCBM as acceptors, show power-conversion efficiencies (PCEs) up to 2.9%, values obtained without extensive optimization work. Furthermore, atomic force microscopy and field-effect transistor (FET) mobility measurements of acceptor-polymer mixtures show that differences in substitution on the polymers affect morphology, mobility, and device performance. Within the series of polymers, all showing similar optical absorption and redox behavior, substituents play an important role in phase separation on a micrometer scale, which in turn has a large impact on device performance. The phase-separation behavior is clearly seen in [70]PCBM devices where the best-performing devices are obtained using the polymers with short alkoxy groups or no substituents together with a high speed of spin coating during device preparation.
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| 7. |
- Ma, Zaifei, et al.
(författare)
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A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer
- 2014
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:6, s. Art. no. 1301455-
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Tidskriftsartikel (refereegranskat)abstract
- This study describes the synthesis and characterization of four polymers based on benzo[1,2-b:4,5-b']dithiophene (BDT) and isoindigo with zero, one, two, and three thiophene spacer groups. Results have demonstrated that the use of bithiophene as a spacer unit improves the geometry of the polymer chain, making it planar, and hence, potentially enhanced π- π stacking occurs. Due to favorable interaction of the polymer chains, enhanced absorption coefficient, and optimal morphology, PBDT-BTI, which possesses bithiophene as a spacer, revealed high current and fill factor leading to a power conversion efficiency of 7.3% in devices, making this polymer the best performing isoindigo-based material in polymer solar cells (PSCs). Also, PBDT-BTI could still maintain efficiency of over 6% with the active layer thickness of 270 nm, making it a potential candidate for a material in printed PSCs. These results demonstrate that the use of thiophene spacers in D-A polymers could be an important design strategy to produce high-performance PSCs.
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| 10. |
- Wang, Ergang, 1981, et al.
(författare)
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Small Band Gap Polymers Synthesized via a Modified Nitration of 4,7-Dibromo-2,1,3-benzothiadiazole
- 2010
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7052 .- 1523-7060. ; 12:20, s. 4470-4473
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Tidskriftsartikel (refereegranskat)abstract
- The nitration of 4,7-dibromo-2,1,3-benzothiadiazole was modified by using CF3SO3H and HNO3 as the nitrating agent, and the related yield was improved greatly. On the basis of this improvement, two new small band gap polymers, P1TPQ and P3TPQ, were developed. Bulk heterojunction solar cells based on P3TPO and [6,6]-phenyl-C-71-butyric acid methyl ester exhibit interesting results with a power conversion efficiency of 21% and photoresponse up to 1.1 mu m
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