| 31. |
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| 32. |
- 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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| 33. |
- Kroon, Renee, 1982, et al.
(författare)
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A New Tetracyclic Lactam Building Block for Thick, Broad-Bandgap Photovoltaics
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 136:33, s. 11578-11581
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Tidskriftsartikel (refereegranskat)abstract
- A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on pi-stacking of the polymer backbone, which was retained in PTNT:firllerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 596 for greater than200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of greater than4% could be retained when thick active layers of similar to 400 rim were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials.
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| 34. |
- Li, Weiwei, et al.
(författare)
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The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices
- 2011
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Ingår i: Organic electronics. - : Elsevier Science B.V., Amsterdam.. - 1566-1199 .- 1878-5530. ; 12:9, s. 1544-1551
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Tidskriftsartikel (refereegranskat)abstract
- How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C(71)-butyric acid methyl ester (PC(71)BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year.
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| 35. |
- Lindqvist, Camilla, et al.
(författare)
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Fullerene mixtures enhance the thermal stability of a non-crystalline polymer solar cell blend
- 2014
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:15, s. 153301-
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Tidskriftsartikel (refereegranskat)abstract
- Printing of polymer: fullerene solar cells at high speed requires annealing at temperatures up to 140 degrees C. However, bulk-heterojunction blends that comprise a non-crystalline donor polymer often suffer from insufficient thermal stability and hence rapidly coarsen upon annealing above the glass transition temperature of the blend. In addition, micrometer-sized fullerene crystals grow, which are detrimental for the solar cell performance. In this manuscript, we present a strategy to limit fullerene crystallization, which is based on the use of fullerene mixtures of the two most common derivatives, PC61BM and PC71BM, as the acceptor material. Blends of this fullerene mixture and a non-crystalline thiophene-quinoxaline copolymer display considerably enhanced thermal stability and largely retain their photovoltaic performance upon annealing at elevated temperatures as high as 170 degrees C.
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| 36. |
- Lindqvist, Camilla, 1985, et al.
(författare)
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Fullerene Nucleating Agents: A Route Towards Thermally Stable Photovoltaic Blends
- 2014
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:9, s. 1301437-
-
Tidskriftsartikel (refereegranskat)abstract
- The bulk-heterojunction nanostructure of non-crystalline polymer: fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non-crystalline thiophene-quinoxaline copolymer and the widely used fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). To this end, C-60 fullerene is employed to efficiently nucleate PCBM crystallization. Sub-micrometer-sized fullerene crystals are formed when as little as 2 wt% C-60 with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C-60. Solar cells based on C-60-nucleated blends indicate significantly improved thermal stability of the bulk-heterojunction nanostructure even after annealing at an elevated temperature of 130 degrees C, which lies above the glass transition temperature of the blend. Moreover, we find that various other compounds, including C-70 fullerene, single-walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents-commonly used to clarify isotactic polypropylene-permit to control crystallization of the fullerene phase.
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| 37. |
- Lorrmann, J, et al.
(författare)
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Charge carrier extraction by linearly increasing voltage: Analytic framework and ambipolar transients
- 2010
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Ingår i: JOURNAL OF APPLIED PHYSICS. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 108:11, s. 113705-
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Tidskriftsartikel (refereegranskat)abstract
- Up to now the basic theoretical description of charge extraction by linearly increasing voltage (CELIV) is solved for a low conductivity approximation only. Here we present the full analytical solution, thus generalize the theoretical framework for this method. We compare the analytical solution and the approximated theory, showing that especially for typical organic solar cell materials the latter approach has a very limited validity. Photo-CELIV measurements on poly(3-hexyl thiophene-2,5-diyl):[6,6]-phenyl-C-61 butyric acid methyl ester based solar cells were then evaluated by fitting the current transients to the analytical solution. We found that the fit results are in a very good agreement with the experimental observations, if ambipolar transport is taken into account, the origin of which we will discuss. Furthermore we present parametric equations for the mobility and the charge carrier density, which can be applied over the entire experimental range of parameters.
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| 38. |
- 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
-
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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| 39. |
- Ma, Zaifei, et al.
(författare)
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Influences of Surface Roughness of ZnO Electron Transport Layer on the Photovoltaic Performance of Organic Inverted Solar Cells
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:46, s. 24462-24468
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Tidskriftsartikel (refereegranskat)abstract
- Here, we demonstrate the correlation between the surface roughness of the ZnO interlayer used as an electron transporting interlayer (ETL) in organic inverted solar cells (ISCs) and the photovoltaic performance of the ISCs. Three different surfaces of the ZnO ETL are studied in ISCs with the polymer poly[2,3-bis-(3-octyloxyphenyl)-quinoxaline-5,8-diyl-alt-thiophene-2,5-d iyl] (TQ1) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the active layer. The results obtained from these ISCs show that power conversion efficiency increases from 2.7% to 3.9% when the root-mean-square roughness of the ZnO layer decreases from 48 to 1.9 nm. Moreover, it is found that the short-circuit current density is higher in the ISC based on the smoother ZnO interlayer, with a larger donor/acceptor (D/A) interfacial area in the active layer that facilitates exciton dissociation. The reduced effective interfacial area between the photoactive layer and the ZnO interlayer with decreased ZnO surface roughness leads to an observed improvement in both fill factor and open circuit voltage, which is ascribed to a reduced concentration of traps at the interface between the ZnO interlayer and the active layer.
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| 40. |
- Ma, Zaifei, et al.
(författare)
-
Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
- 2014
-
Ingår i: energy and environmental science. - : Royal Society of Chemistry. - 1754-5692. ; 17:1, s. 361-369
-
Tidskriftsartikel (refereegranskat)abstract
- A series of alternating oligothiophene (nT)-isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both, polymer crystallinity and polymer-fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of favorable morphology and optimal interface energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work is a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc.
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