| 1. |
- Diaz de Zerio Mendaza, Amaia, 1986, et al.
(författare)
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A Fullerene Alloy Based Photovoltaic Blend with a Glass Transition Temperature above 200 °C
- 2017
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Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 5:8, s. 4156-4162
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Tidskriftsartikel (refereegranskat)abstract
- Organic solar cells with a high degree of thermal stability require bulk-heterojunction blends that feature a high glass transition, which must occur considerably above the temperatures encountered during device fabrication and operation. Here, we demonstrate for the first time a polymer : fullerene blend with a glass transition temperature above 200 °C, which we determine by plasmonic nanospectroscopy. We achieve this strong tendency for glass formation through the use of an alloy of neat, unsubstituted C60 and C70, which we combine with the fluorothieno-benzodithiophene copolymer PTB7. A stable photovoltaic performance of PTB7 : C60 : C70 ternary blends is preserved despite annealing the active layer at up to 180 °C, which coincides with the onset of the glass transition. Rapid deterioration of the power conversion efficiency from initially above 5% only occurs upon exceeding the glass transition temperature of 224 °C of the ternary blend.
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| 2. |
- Nugroho, Ferry, 1986, et al.
(författare)
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Plasmonic Nanospectroscopy for Thermal Analysis of Organic Semiconductor Thin Films
- 2017
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 89:4, s. 2575-2582
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Tidskriftsartikel (refereegranskat)abstract
- Organic semiconductors are key materials for the next generation of thin film electronic devices like field-effect transistors, light-emitting diodes and solar cells. Accurate thermal analysis is essential for the fundamental understanding of these materials, for device design, stability studies and quality control because desired nanostructures are often far from thermodynamic equilibrium and therefore tend to evolve with time and temperature. However, classical experimental techniques are insufficient because the active layer of most organoelectronic device architectures is typically only on the order of hundred nanometers or less. Scrutinizing the thermal properties in this size range is, however, critical because strong deviations of the thermal properties from bulk values due to confinement effects, and due to pronounced influence of the substrate become significant. Here, we introduce plasmonic nanospectroscopy as an experimental approach to scrutinize the thickness dependence of the thermal stability of semi-crystalline, liquid-crystalline and glassy organic semiconductor thin films down to the sub-100 nm film thickness regime. As the main result we find a pronounced thickness dependence of the glass transition temperature of ternary polymer:fullerene blend thin films, and their constituents, which can be resolved with exceptional precision by the plasmonic nanospectroscopy method, that relies on remarkably simple instrumentation.
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| 3. |
- Bäcke, Olof, 1984, et al.
(författare)
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Enhanced thermal stability of a polymer solar cell blend induced by electron beam irradiation in the transmission electron microscope
- 2017
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 173, s. 16-23
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Tidskriftsartikel (refereegranskat)abstract
- We show by in situ microscopy that the effects of electron beam irradiation during transmission electron microscopy can be used to lock microstructural features and enhance the structural thermal stability of a nanostructured polymer:fullerene blend. Polymer:fullerene bulk-heterojunction thin films show great promise for use as active layers in organic solar cells but their low thermal stability is a hindrance. Lack of thermal stability complicates manufacturing and influences the lifetime of devices. To investigate how electron irradiation affects the thermal stability of polymer:fullerene films, a model bulk-heterojunction film based on a thiophene-quinoxaline copolymer and a fullerene derivative was heat-treated in-situ in a transmission electron microscope. In areas of the film that exposed to the electron beam the nanostructure of the film remained stable, while the nanostructure in areas not exposed to the electron beam underwent large phase separation and nucleation of fullerene crystals. UV–vis spectroscopy shows that the polymer:fullerene films are stable for electron doses up to 2000 kGy.
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| 4. |
- Bäcke, Olof, 1984, et al.
(författare)
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Enhanced thermal stability of a polymer solar cell blend induced by electron beam irradiation in the transmission electron microscope
- 2017
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 176:Spec. Issue, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- We show by in situ microscopy that the effects of electron beam irradiation during transmission electron microscopy can be used to lock microstructural features and enhance the structural thermal stability of a nanostructured polymer:fullerene blend. Polymer:fullerene bulk-heterojunction thin films show great promise for use as active layers in organic solar cells but their low thermal stability is a hindrance. Lack of thermal stability complicates manufacturing and influences the lifetime of devices. To investigate how electron irradiation affects the thermal stability of polymer:fullerene films, a model bulk-heterojunction film based on a thiophene-quinoxaline copolymer and a fullerene derivative was heat-treated in-situ in a transmission electron microscope. In areas of the film that exposed to the electron beam the nanostructure of the film remained stable, while the nanostructure in areas not exposed to the electron beam underwent large phase separation and nucleation of fullerene crystals. UV–vis spectroscopy shows that the polymer:fullerene films are stable for electron doses up to 2000 kGy.
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| 5. |
- Bäcke, Olof, 1984, et al.
(författare)
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Mapping fullerene crystallization in a photovoltaic blend: an electron tomography study
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:18, s. 8451-8456
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Tidskriftsartikel (refereegranskat)abstract
- The formation of fullerene crystals represents a major degradation pathway of polymer/fullerene bulk-heterojunction thin films that inexorably deteriorates their photovoltaic performance. Currently no tools exist that reveal the origin of fullerene crystal formation vertically through the film. Here, we show that electron tomography can be used to study nucleation and growth of fullerene crystals. A model bulk-heterojunction blend based on a thiophene-quinoxaline copolymer and a fullerene derivative is examined after controlled annealing above the glass transition temperature. We image a number of fullerene nanocrystals, ranging in size from 70 to 400 nanometers, and observe that their center is located close to the free-surface of spin-coated films. The results show that the nucleation of fullerene crystals predominately occurs in the upper part of the films. Moreover, electron tomography reveals that the nucleation is preceded by more pronounced phase separation of the blend components.
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| 6. |
- Diaz de Zerio Mendaza, Amaia, 1986, et al.
(författare)
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Glass Forming Acceptor Alloys for Highly Efficient and Thermally Stable Ternary Organic Solar Cells
- 2018
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 8:28
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Tidskriftsartikel (refereegranskat)abstract
- The stability of donor:acceptor (D:A) semiconductor blends plays a key role in the development of solution-processed organic solar cells. One essential condition for both high-yield production and a long lifetime is excellent thermal stability. Recently, A1:A2 acceptor mixtures have received considerable attention and alloys of two miscible acceptors are singled out as a powerful tool for the design of efficient and durable organic solar cells. This progress report introduces a thermodynamic rationale for the superior thermal stability and reproducibility that is observed for some ternary blends. The increase in entropy upon mixing of several acceptors reduces the tendency for phase separation as well as crystallization, which facilitates the controlled formation of a fine blend nanostructure. Further, when combined with a high glass transition temperature many ternary blends can be readily quenched into a glassy state. Recent progress with regard to the thermal stability and efficiency of D:A1:A2 ternary blends is summarized in the light of the thermodynamic and kinetic arguments discussed in this article. Both, fullerene and fullerene-free acceptor alloys now yield solar cell efficiencies in excess of 10%, which indicates that ternary blends are a promising avenue that is poised to considerably enhance the prospect of organic photovoltaics.
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| 7. |
- Diaz de Zerio Mendaza, Amaia, 1986
(författare)
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Glass-forming ternary blends: towards stable Polymer Solar Cells
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The globally increasing use of electricity goes hand in hand with climate change and the gradual depletion of fossil sources of fuel. To address these challenges renewable sources of energy are in high demand. Solution-processable organic solar cells receive particular attention because they promise to combine a set of highly attractive features including low manufacturing cost through large-area and continuous printing, as well as low weight, flexibility and semitransparency. The stability of the light-harvesting organic photovoltaic materials, which typically consist of a finely mixed blend of an electron donor and acceptor, plays a key role in the development of efficient and durable organic solar cells. One essential condition for both high-yield production and a long lifetime is excellent thermal stability. The organic photovoltaic material must be able to withstand high fabrication and operation temperatures.The aim of this thesis is to explore the use of ternary blends as a tool to improve the often insufficient thermal stability of organic photovoltaic materials. Ternary blends are a relatively new concept within the field of organic photovoltaics. This thesis focuses on blends of a donor polymer and a mixture of the two most common neat fullerenes, C60 and C70. Processing of the neat fullerene alloy is facilitated through a highly advantageous increase in solubility, which is found to correlate with the increase in entropy upon mixing. As a result, solar cells with a power conversion efficiency of 6 % are realized, a record for devices based on neat fullerenes. A high tendency for glass formation of polymer:C60:C70 ternary blends is found to induce a high degree of thermal stability due to a glass transition temperature in excess of 200°C. Vitrification of ternary blends is discussed in terms of the entropy of mixing, which reduces the rate of both crystal nucleation and growth. Finally, this thesis provides an overview of the current state-of-the-art, discussing both fullerene as well as fullerene-free ternary blends.
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| 8. |
- Diaz de Zerio Mendaza, Amaia, 1986, et al.
(författare)
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High-Entropy Mixtures of Pristine Fullerenes for Solution-Processed Transistors and Solar Cells
- 2015
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 27:45, s. 7325-7331
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Tidskriftsartikel (refereegranskat)abstract
- The solubility of pristine fullerenes can be enhanced by mixing C60 and C70 due to the associated increase in configurational entropy. This "entropic dissolution" allows the preparation of field-effect transistors with an electron mobility of 1 cm2 V-1 s-1 and polymer solar cells with a highly reproducible power-conversion efficiency of 6%, as well as a thermally stable active layer.
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| 9. |
- Diaz de Zerio Mendaza, Amaia, 1986, et al.
(författare)
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Neat C60:C70 buckminsterfullerene mixtures enhance polymer solar cell performance
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:35, s. 14354-14359
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that bulk-heterojunction blends based on neat, unsubstituted buckminsterfullerenes (C60, C70) and a thiophene–quinoxaline copolymer (TQ1) can be readily processed from solution. Atomic force and transmission electron microscopy as well as photoluminescence spectroscopy reveal that thin films with a fine-grained nanostructure can be spin-coated, which display a good photovoltaic performance. Replacement of substituted fullerenes with C60 or C70 only results in a small drop in open-circuit voltage from 0.9 V to about 0.8 V. Thus, a power conversion efficiency of up to 2.9% can be maintained if C70 is used as the acceptor material. Further improvement in photovoltaic performance to 3.6% is achieved, accompanied by a high internal quantum efficiency of 75%, if a 1 : 1 C60:C70 mixture is used as the acceptor material, due to its improved solubility in ortho-dichlorobenzene.
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| 10. |
- Holmes, N. P., et al.
(författare)
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Nano-pathways: Bridging the divide between water-processable nanoparticulate and bulk heterojunction organic photovoltaics
- 2016
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855. ; 19, s. 495-510
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Tidskriftsartikel (refereegranskat)abstract
- Here we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-di yl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (T-g) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC71BM (phenyl C-71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the T-g (sub-T-g and post-T-g), both in the active layer drying stage and post-cathode deposition annealing stage of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. In addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously-been observed, that of PC71BM nano-pathway formation between dispersed PC71BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction.
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| 11. |
- 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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| 12. |
- Kroon, Renee, 1982, et al.
(författare)
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Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells
- 2015
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Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 6:42, s. 7402-7409
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we compare the effect of incorporating selenophene versus thienothiophene spacers into pentacyclic lactam-based conjugated polymers for organic solar cells. The two cyclic lactam-based copolymers were obtained via a new synthetic method for the lactam moiety. Selenophene incorporation results in a broader and red-shifted optical absorption while retaining a deep highest occupied molecular orbital level, whereas thienothienophene incorporation results in a blue-shifted optical absorption. Additionally, grazing-incidence wide angle X-ray scattering data indicates edge- and face-on solid state order for the selenophene-based polymer as compared to the thienothiophene-based polymer, which orders predominantly edge-on with respect to the substrate. In polymer : PC71BM bulk heterojunction solar cells both materials show a similar open-circuit voltage of similar to 0.80-0.84 V, however the selenophene-based polymer displays a higher fill factor of similar to 0.70 vs. similar to 0.65. This is due to the partial face-on backbone orientation of the selenophene-based polymer, leading to a higher hole mobility, as confirmed by single-carrier diode measurements, and a concomitantly higher fill factor. Combined with improved spectral coverage of the selenophene-based polymer, as confirmed by quantum efficiency experiments, it offers a larger short-circuit current density of similar to 12 mA cm(-2). Despite the relatively low molecular weight of both materials, a very robust power conversion efficiency similar to 7% is achieved for the selenophene-based polymer, while the thienothiophene-based polymer demonstrates only a moderate maximum PCE of similar to 5.5%. Hence, the favorable effects of selenophene incorporation on the photovoltaic performance of pentacyclic lactam-based conjugated polymers are clearly demonstrated.
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| 13. |
- Lombeck, F., et al.
(författare)
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On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells
- 2016
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 6:21
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties and solar cell performance of the classical donor-acceptor copolymer PCDTBT(poly(N-9-heptadecanyl-2,7-carbazole-alt -5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole-carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time-dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents J(SC). With increasing Cbz hc content, J(SC) decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in J(SC) alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling-free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.
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| 14. |
- Pan, Xun, et al.
(författare)
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Environmentally friendly preparation of nanoparticles for organic photovoltaics
- 2018
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Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 59, s. 432-440
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous nanoparticle dispersions were prepared from a conjugated polymer poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3′,2′-h][1,5]naphthyridine-2,7-diyl] (PTNT) and fullerene blend utilizing chloroform as well as a non-chlorinated and environmentally benign solvent, o-xylene, as the miniemulsion dispersed phase solvent. The nanoparticles (NPs) in the solid-state film were found to coalesce and offered a smooth surface topography upon thermal annealing. Organic photovoltaics (OPVs) with photoactive layer processed from the nanoparticle dispersions prepared using chloroform as the miniemulsion dispersed phase solvent were found to have a power conversion efficiency (PCE) of 1.04%, which increased to 1.65% for devices utilizing NPs prepared from o-xylene. Physical, thermal and optical properties of NPs prepared using both chloroform and o-xylene were systematically studied using dynamic mechanical thermal analysis (DMTA) and photoluminescence (PL) spectroscopy and correlated to their photovoltaic properties. The PL results indicate different morphology of NPs in the solid state were achieved by varying miniemulsion dispersed phase solvent.
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| 15. |
- Tian, Yuxi, et al.
(författare)
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Molecular Weight Determination by Counting Molecules
- 2015
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1089-5639 .- 1520-5215. ; 6:6, s. 923-927
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Tidskriftsartikel (refereegranskat)abstract
- Molecular weight (MW) is one of the most important characteristics of macromolecules. Sometimes, MW cannot be measured correctly by conventional methods like gel permeation chromatography (GPC) due to, for example, aggregation. We propose using single-molecule spectroscopy to measure the average MW simply by counting individual fluorescent molecules embedded in a thin matrix film at known mass concentration. We tested the method on dye molecules, a labeled protein, and the conjugated polymer MEH-PPV. We showed that GPC with polystyrene calibration overestimates the MW of large MEH-PPV molecules by 40 times due to chain aggregation and stiffness. This is a crucial observation for understanding correlations between the conjugated polymer length, photophysics and performances of devices. The method can measure the MW of fluorescent molecules, biological objects, and nanoparticles at ultimately low concentrations and does not need any reference; it is conformation-independent and has no limitations regarding the detected MW range.
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