| 1. |
- Cai, Tianqi, et al.
(författare)
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Low bandgap polymers synthesized by FeCl(3) oxidative polymerization
- 2010
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248. ; 94:7, s. 1275-1281
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Tidskriftsartikel (refereegranskat)abstract
- Four low bandgap polymers, combining an alkyl thiophene donor with benzo[c][1,2,5]thiadiazole, 2,3-diphenylquinoxaline, 2,3-diphenylthieno[3,4-b]pyrazine and 6,7-diphenyl-[1,2,5]thiadiazolo[3,4-g] quinoxaline acceptors in a donor-acceptor-donor architecture, were synthesized via FeCl3 oxidative polymerization. The molecular weights of the polymers were improved by introducing o-dichlor-obenzene (ODCB) as the reaction solvent instead of the commonly used solvent, chloroform. The photophysical, electrochemical and photovoltaic properties of the resulting polymers were investigated and compared. The optical bandgaps of the polymers vary between 1.0 and 1.9 eV, which is promising for solar cells. The devices spin-coated from an ODCB solution of P1DB:[70]PCBM showed a power conversion efficiency of 1.08% with an open-circuit voltage of 0.91 V and a short-circuit current density of 3.36 mA cm(-2) under irradiation from an AM1.5G solar simulator (100 mW cm(-2)). (C) 2010 Elsevier B.V. All rights reserved.
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| 2. |
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| 3. |
- 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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| 4. |
- George, Zandra, 1985, et al.
(författare)
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The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells
- 2013
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 6:7, s. 3022-3034
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Tidskriftsartikel (refereegranskat)abstract
- A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure.
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| 5. |
- Hellström, Stefan, 1978, et al.
(författare)
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Blue-to-transmissive electrochromic switching of solution processable donor-acceptor polymers
- 2011
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 12:8, s. 1406-1413
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Tidskriftsartikel (refereegranskat)abstract
- The electrochromic performance of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diylalt-thiophene-2,5-diy l] (TQ1), switching from an intense blue color to a transmissive yellow-brown oxidized state, are presented. Additionally, two new polymers, based on the same polymeric backbone but with oligoethylene oxide (TQ2) and ethylhexyloxy (TQ3) side chains, were prepared to compare the structure-property relationships. TQ1 has the highest optical contrast, with a transmittance change of 50%, recorded by spectroelectrochemistry at the low-energy absorption maximum (623 nm). The high optical contrast, facile synthetic preparation, and processability through good solubility in organic solvents make TQ1 an interesting polymer for implementation in non-emissive electrochromic devices. Response times were improved by the introduction of ethylhexyloxy side chains (TQ3), where 92% of the transmittance modulation was maintained at switching times of 0.5 s. The influence of film thickness on optical contrast was also investigated, where the highest optical contrast for TQ1 was obtained for films having reduced absorption of 0.84 a.u. at the low-energy absorption maximum. All three polymers show decent electrochemical stability over 200 full switches.
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| 6. |
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| 7. |
- Hellström, Stefan, 1978, et al.
(författare)
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Influence of side chains on electrochromic properties of green donor-acceptor-donor polymers
- 2011
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 56:10, s. 3454-3459
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Tidskriftsartikel (refereegranskat)abstract
- Three solution processable cathodically coloring green electrochromic polymers, based on 2,3-diphenyl-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine, have been synthesized by oxidative FeCl3 polymerization. The polymers were designed with solubilizing alkyl and oligoethylene oxide side chains to achieve solubility and processability. All three polymers have a small electrochemical bandgap (1.8-1.9 eV) and low oxidation potentials. Spectroelectrochemical studies of polymer films on ITO reveal that the alkyl side chains in head-to-head position on the polymer backbone promote a defined high-energy absorption peak and suppress tailing of charge-carrier absorption into the visible region. Kinetic studies, based on transmission measurements applying a square-wave potential between reduced and oxidized states, show that the polymer with exclusively oligoethylene oxide side chains (P3) had the fastest response times, monitored at the low-energy absorption maxima. The best performing polymer (P1) showed a good optical contrast in the visible region with a Delta T of 26% at 700 nm. An initial test of the electrochemical stability showed that the oligoethylene oxide containing polymers had superior stability over 500 full switches.
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| 8. |
- Hellström, Stefan, 1978, et al.
(författare)
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Structure-property relationships of small bandgap conjugated polymers for solar cells
- 2009
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Ingår i: DALTON TRANSACTIONS. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45, s. 10032-10039
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated polymers as electron donors in solar cells based on donor/acceptor combinations are of great interest, partly due to the possibility of converting solar light with a low materials budget. Six small bandgap polymers with optical bandgap ranging from 1.0-1.9 eV are presented in this paper. All polymers utilize an electron donor-acceptor-donor (DAD) segment in the polymer backbone, creating a partial charge-transfer, to decrease the bandgap. The design, synthesis and the optical characteristics as well as the solar cell characteristics of the polymers are discussed. The positions of the energy levels of the conjugated polymer relative to the electron acceptor are of significant importance and determine not only the driving force for exciton dissociation but also the maximum open-circuit voltage. This work also focuses on investigating the redox behavior of the described conjugated polymers and electron acceptors using square wave voltammetry. Comparing the electrochemical data gives important information of the structure-property relationships of the polymers.
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| 9. |
- Hellström, Stefan, 1978, et al.
(författare)
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Synthesis and characterization of three small band gap conjugated polymers for solar cell applications
- 2010
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 1:8, s. 1272-1280
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new series of small band gap conjugated polymers utilizing donor-acceptor-donor substructures in the polymer backbone to broaden and extend the optical absorption to longer wavelengths. Three polymers were prepared by Suzuki polymerization, using the same donor-acceptor-donor segment but with different comonomers. The goal was to investigate how the optical and electronic properties of the polymers were influenced by the different comonomers. Electrochemical spectroscopy, using square-wave voltammetry, shows that increasing the electron-donating strength of the comonomer will raise the HOMO energy level of the polymer, resulting in a decreased band gap. This result is also manifested by comparing open-circuit voltages from the corresponding laboratory fabricated solar cells. The best performing photovoltaic cell, based on APFO-Green15/[60]PCBM (1 : 4 w/w), reached a J(sc) of 4.2 mA cm(-2), a V-oc of 0.73 V, and a FF of 0.54, giving a PCE of 1.7%.
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| 10. |
- Inganäs, Olle, et al.
(författare)
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Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device Architectures
- 2010
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 22:20, s. E100-E116
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of novel conjugated polymers, designed for the purpose of photovoltaic energy conversion, and their properties in polymer/fullerene materials and photovoltaic devices are reviewed. Two families of main chain polymer donors, based on fluorene or phenylene and donor-acceptor-donor comonomers in alternating copolymers, are used to absorb the high-energy parts of the solar spectrum and to give high photovoltages in combinations with fullerene acceptors in devices. These materials are used in alternative photovoltaic device geometries with enhanced light incoupling to collect larger photocurrents or to enable tandem devices and enhance photovoltage.
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