| 1. |
- Zhuang, Wenliu, 1979, et al.
(författare)
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Influence of Incorporating Different Electron-Rich Thiophene-Based Units on the Photovoltaic Properties of Isoindigo-Based Conjugated Polymers: An Experimental and DFT Study
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 46:21, s. 8488-8499
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel donor–acceptor conjugated alternating copolymers based on the isoindigo acceptor moiety have been designed, synthesized, and characterized, in order to explore the potential of isoindigo for efficient donor materials with high photovoltages in solar cells. We have systematically investigated and discussed the effect of combining different electron-rich thiophene-based units on the structural, optical, electronic, and photovoltaic properties of the resulting polymers. Morphological studies and quantum-chemical calculations are carried out to gain insights into the different properties. The power conversion efficiencies (PCEs) of the solar cells based on these polymers are increased step by step by over 3-fold through a rational structural modification. Among them, PBDTA-MIM shows a PCE of 5.4%, which is to our knowledge the best result achieved among isoindigo-based polymers for solar cells combined with PC61BM as the acceptor using the conventional device configuration. Our results further emphasize the use of isoindigo as an effective acceptor unit and highlight the importance of carefully choosing appropriate chemical structure to design efficient donor–acceptor polymers for organic solar cells. In addition, the resulting low optical gaps, the promising PCEs with PC61BM as the acceptor, and the good open-circuit voltages (up to 0.8 V) synergistically demonstrate the potential of this class of polymers as donor materials for bottom subcells in organic tandem solar cells.
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| 2. |
- Bergqvist, Jonas, et al.
(författare)
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Asymmetric photocurrent extraction in semitransparent laminated flexible organic solar cells
- 2018
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Ingår i: npj Flexible Electronics. - : Springer Science and Business Media LLC. - 2397-4621. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Scalable production methods and low-cost materials with low embodied energy are key to success for organic solar cells. PEDOT(PSS) electrodes meet these criteria and allow for low-cost and all solution-processed solar cells. However, such devices are prone to shunting. In this work we introduce a roll-to-roll lamination method to construct semitransparent solar cells with a PEDOT(PSS) anode and an polyethyleneimine (PEI) modified PEDOT(PSS) cathode. We use the polymer:PCBM active layer coated on the electrodes as the lamination adhesive. Our lamination method efficiently eliminates any shunting. Extended exposure to ambient degrades the laminated devices, which manifests in a significantly reduced photocurrent extraction when the device is illuminated through the anode, despite the fact that the PEDOT(PSS) electrodes are optically equivalent. We show that degradation-induced electron traps lead to increased trap-assisted recombination at the anode side of the device. By limiting the exposure time to ambient during production, degradation is significantly reduced. We show that lamination using the active layer as the adhesive can result in device performance equal to that of conventional sequential coating.
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| 3. |
- Bolognesi, Margherita, et al.
(författare)
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2D π-conjugated benzo[1,2-b:4,5-b']dithiophene- and quinoxaline-based copolymers for photovoltaic applications
- 2013
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Ingår i: RSC Advances. - 2046-2069. ; 3:46, s. 24543-24552
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Tidskriftsartikel (refereegranskat)abstract
- Two medium gap semiconducting polymers, P(1)-Q-BDT-4TR and P(2)-FQ-BDT-4TR, based on alternate units of alkyl-dithiophene substituted benzodithiophene (BDT) and quinoxaline units (without or with fluorine substitution), are synthesized and fully characterized. The polymers exhibit optical and electrical properties favorable for being employed as donors in BHJ OPV devices, such as: absorption spectra extending up to around 720 nm for a high solar spectrum coverage, deep lying HOMO energy levels for a high device open circuit voltage and LUMO energy levels higher than those of PC61BM and PC71BM for an efficient exciton dissociation. In particular, the presence of alkyl-dithiophene side chains allows us to obtain a high 2D π-conjugation which promotes red shifted absorption profiles, low HOMO energy levels (
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| 4. |
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| 5. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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An alternating copolymer of fluorene donor and quinoxaline acceptor versus a terpolymer consisting of fluorene, quinoxaline and benzothiadiazole building units: synthesis and characterization
- 2016
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Ingår i: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 73:4, s. 1167-1183
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Tidskriftsartikel (refereegranskat)abstract
- An alternating polyfluorene copolymer based on fluorene donor and quinoxaline acceptor (P1) and an alternating terpolymer (P2) with fluorene (50 %) donor and quinoxaline (25 %) and benzothiadiazole (25 %) acceptor units were designed and synthesized for use as photoactive materials in solar cells. The presence of benzothiadiazole unit in P2 increased the optical absorption coverage in the range of 350-600 nm, which is an interesting property and a big potential for achieving improved photovoltaic performances with judicious optimization of the devices. Solar cells were fabricated from 1:4 blends of polymers-PCBM[70] using o-dichlorobenzene (o-DCB) as processing solvent, and P1 showed a power conversion efficiency (PCE) of 3.18 %, with a short-circuit current density (J (SC)) of 7.78 mA/cm(2), an open-circuit voltage (V (OC)) of 0.82 V, and a fill factor (FF) of 50 % while P2 showed an overall PCE of 2.14 % with corresponding J (SC) of 5.97 mA/cm(2), V (OC) of 0.84 V and FF of 42 %. In general, P2 gave lower J (SC) and FF presumably due to the fine domain sizes of the polymer-PCBM[70] blend as seen from the atomic force microscopy (AFM) image which might have affected the charge carrier transport. Alternating (P1) and ternary (P2) conjugated polymers were designed, synthesized and used for fabrication of photovoltaic devices.
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| 6. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Conjugated polymers based on benzodithiophene and fluorinated quinoxaline for bulk heterojunction solar cells: thiophene versus thieno[3,2-b]thiophene as π-conjugated spacers
- 2014
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Ingår i: Polymer Chemistry. - 1759-9954 .- 1759-9962. ; 5:6, s. 2083-2093
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Tidskriftsartikel (refereegranskat)abstract
- Two conjugated donor–acceptor copolymers based on a benzodithiophene donor unit and a fluorinated quinoxaline acceptor unit, spaced with either thiophene or thieno[3,2-b]thiophene π-bridges, were designed and synthesized. The effect of different π-bridges and of the processing conditions on the optical, electrical, morphological and photovoltaic properties of the polymer:fullerene blend films were investigated. The polymer containing the thieno[3,2-b]thiophene π-bridge (PBDTFQ-TT) showed a red-shifted absorption and enhanced charge carrier mobility, as compared to its analogue with the thiophene π-bridge (PBDTFQ-T), due to its narrower optical gap (by ~ 0.1 eV) and stronger inter-chain interactions, favored by the structural planarity and increased linearity of the polymer backbone, as also supported by DFT calculations. The blend of PBDTFQ-TT and PC61BM ([6,6]-phenyl-C61-butyric acid methyl ester), compared to the PBDTFQ-T:PC61BM one processed in the same conditions (by blade-coating technique), showed greatly enhanced photovoltaic performance, with more than doubled power conversion efficiency (PCE up to 5.60% for the best device) due to the increased short-circuit current density and fill factor. However, similar PCEs were also achieved for PBDTFQ-T:PC61BM-based devices by optimizing the processing conditions through the addition of 1,8-diiodooctane (DIO) as the solvent additive. Through morphological and electrical analysis of the films, produced with and without additive, it was observed that the addition of DIO greatly enhances the self-organization, and consequently the charge mobility, of the thiophene π-bridge-based polymer, while it was detrimental for the nanoscale morphology and photovoltaic performances of the thieno[3,2-b]thiophene π-bridge-based polymer in the corresponding blend.
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| 7. |
- 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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| 8. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Induced photodegradation of quinoxaline based copolymers for photovoltaic applications
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248. ; 144, s. 150-158
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Tidskriftsartikel (refereegranskat)abstract
- We report here the synthesis and characterization of a series of p-type copolymers, which combine a fluorinated quinoxaline (FQ) acceptor unit either with a differently substituted benzodithiophene (BDT) or an unsubstituted thieno[3,2-b]thiophene (TT). The effect of the structural modifications on the photochemical stability of the resulting films is investigated and then correlated with the photovoltaic performance and lifetime measurements of corresponding photovolatic devices. To this end, we firstly studied the intrinsic stability of each polymer film by monitoring the UV-vis absorption decay, under simulated sunlight, as a function of ageing time. Bulk heterojunction solar cells, based on these polymers as donor materials, were fabricated and tested. Beside the initial values, we monitored the photovoltaic performance during prolonged light soaking in order to evaluate and compare the photostability of more complex systems such as working solar cells.
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| 9. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Optimization of the power conversion efficiency in high bandgap pyridopyridinedithiophene-based conjugated polymers for organic photovoltaics by the random terpolymer approach
- 2017
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Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057. ; 91, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- We report that the organic photovoltaic (OPV) performance of wide band gap pyridopyridinedithiophene-based conjugated polymers can be significantly improved by employing the random terpolymer approach for the development of new pyridopyridinedithiophene-based conjugated polymers. This is demonstrated by the synthesis of the alternating copolymer (P1) consisting of 3,3?-difluoro-2,2?-bithiophene and pyridopyridinedithiophene and the random terpolymer (P2) containing pyridopyridinedithiophene 3,3?-difluoro-2,2?-bithiophene and thiophene. OPV devices fabricated by P1 and P2 in combination with PC61BM and PC71BM in an inverted device configuration exhibited power conversion efficiencies (PCEs) of 1.5% and 4.0%, respectively. We identified that the main reason for the enhanced performance of the OPV devices based on the P2 random copolymer was the improved morphology (miscibility) between P2 and PCBM as compared to P1. More specifically, atomic force microscopy (AFM) and scanning electron microscopy (SEM) studies revealed that the P1 based films showed rougher surface with clear crystallization/precipitation of the polymer chains even after the addition of chloronaphthalene (CN) to the chloroform processing solvent which significantly limited the short circuit current density (JSC), fill factor (FF) and overall performance of the prepared photovoltaic devices. On the other hand, P2 based films showed better miscibility with the acceptor particularly when processed using 5% CN containing chloroform solvent giving a respectable improvement in the PCE of the photovoltaic devices.
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| 10. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
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Random polyfluorene co-polymers designed for a better optical absorption coverage of the visible region of the electromagnetic spectrum
- 2014
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Ingår i: Bulletin of the Chemical Society of Ethiopia. - : African Journals Online (AJOL). - 1726-801X .- 1011-3924. ; 28:1, s. 121-130
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Tidskriftsartikel (refereegranskat)abstract
- Two alternating polyfluorenes (APFO15-F8BT and APFO3-F8BT) with full absorption of the visible region of the electromagnetic radiation were designed and synthesized for bulk-heterojunction solar cell devices. The optical and electrochemical properties of the two polymers were studied. The two polymers exhibited strong absorption in the visible region with no significant valley over the visible region extending up to 650 nm. Deep HOMO and ideally situated LUMO energy levels were the characteristics of the two polymers as revealed from the square wave voltammogram study: desired properties for extracting high open circuit voltage and for a facile charge transfer to the acceptor component in devices to take place, respectively. Photovoltaic devices were fabricated by blending the two polymers with PCBM[70] and up to similar to 2% power conversion efficiency were obtained.
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