| 1. |
- Ericsson, Leif, 1964-, et al.
(författare)
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An experimental setup for dip-coating of thin films for organic solar cells under microgravity conditions
- 2021
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the design and testing of a custom-built experimental setup for dip-coating from volatile solutions under microgravity conditionsonboard an aircraft. Function and safety considerations for the equipment are described. The equipment proved to work well, both concerningthe safety and the preparation of thin films. No leakage of the solvents, nor the solvent vapors, was detected, not even in a situation with afluctuating gravitational field due to bad weather conditions. We have shown that the equipment can be used to prepare thin films of polymerblends, relevant for organic solar cells, from solution in a feasible procedure under microgravity conditions. The prepared films are similar tothe corresponding films prepared under 1 g conditions, but with differences that can be related to the absence of a gravitational field duringdrying of the applied liquid coating. We report on some introductory results from the characterization of the thin films that show differencesin film morphology and structure sizes.
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| 2. |
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| 3. |
- Jalan, Ishita, 1991-, et al.
(författare)
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Donor-acceptor polymer complex formation in solution confirmed by spectroscopy and atomic-scale modelling
- 2023
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 11:27, s. 9316-9326
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Tidskriftsartikel (refereegranskat)abstract
- In all-polymer solar cells, high performance is attributed to the fine-grained morphology of the film in the active layer. However, the mechanism by which this fine-grained morphology is achieved remains unknown. Polymeric non-fullerene acceptors have the potential to restrict the self-aggregation, typical of non-fullerene small molecule acceptors. Here we employed a blend of the polymeric acceptor PF5-Y5 and the donor polymer PBDB-T to investigate the balance between molecular interactions in solution. Temperature-dependent absorption spectra show evidence of temperature-induced disaggregation of both donor and acceptor polymers, where the donor polymer disaggregation depends on the solvent polarity. Concentration-dependent fluorescence spectra of blend solutions display blue-shifted acceptor emission upon dilution, similar to that observed in acceptor solutions, and a decreased tendency for charge transfer from donor to acceptor upon dilution. Excitation spectra of dilute blend solutions contain an increased contribution to the long-wavelength acceptor emission, as compared to pure acceptor solutions, from a chromophore that absorbs in a region where the donor does not absorb. These observations can be explained by donor-acceptor complexation in dilute blend solutions, that is stabilized in more polar solvents. Moreover, the near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. The results corroborate that the interaction between segments of the donor and acceptor polymer chains favours the formation of donor-acceptor charge transfer complexes, stabilized by hybridization of the molecular orbitals, which reduces the electronic energy. The proposed donor-acceptor complex formation competes with the donor and acceptor self-aggregation and is influenced by the solvent environment. These pre-formed donor-acceptor complexes in low-concentration solutions can be expected to have important consequences on the film morphology of all-polymer blends. The results from this joint experimental-theoretical spectroscopy study provide insights that can guide the design of compatible donor and acceptor polymers for future high-performance organic solar cells.
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| 4. |
- Jalan, Ishita, 1991-
(författare)
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Film morphology for organic solar cells : Effect of Solubility and Gravity Conditions
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic photovoltaics is a promising environmentally friendly technology, due to their printability, light-weight nature and mechanical flexibility, and the possibility to use off-grid. Research and development in this field has resulted in power conversion efficiencies of over 15%. To further improve the efficiency, it is important to understand the connection between the morphology of the active layer and the performance of the device. This thesis focuses on understanding on a molecular level of the morphology formation in a thin coated film of a polymer bend, using two different approaches. One approach will focus on the thermodynamics of conjugated polymers in relation to the morphology, by using the Hansen solubility Parameters (HSP) and solution chemistry. The second approach focuses on understanding phase separation between the two polymers in the active layer. To be able to study phase separation, films were fabricated under microgravity conditions, as previous studies show that in these conditions phase separation mechanism is slowed down. Atomic force microscopy is used to characterize the resulting morphology of the thin films. Preliminary studies in this thesis showed that using HSP is a good tool, to understanding solvent-solute and solute-solute interactions in solution and to guide the final film morphology in relation to solubility. Furthermore, HSP is a good tool for the preliminary screening of alternative solvents and solvent blends for environmentally friendly processing solvents for upscaling. It was also found that dip coating of films under microgravity conditions provides a tool to study the early stages of the phase separation, as well as facilitate the study of the dependence of the morphology on the thicknesses of the coating. More work is needed to be able to separate the complex effect of hypergravity and to eliminate uncertainty concerning if the deposited wet film is completely dried under the microgravity phase.
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| 5. |
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| 6. |
- Jalan, Ishita, 1991-
(författare)
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Solution Chemistry and Morphological Properties for Organic Solar Cells : Exploring Alternative Solvents Using Microgravity and Modelling as Tools
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic photovoltaics (OPVs) have the advantage of the accessibility of energy for all, due to facile and low-cost processing, with its low energy payback time compared to other technologies, therefore promising applications. Research and development have led to power conversion efficiencies of nearly 20% and now catching up to their inorganic counterparts. To enhance the efficiency even further, it is crucial to get an insight into the correlation between the active layer's morphology and the device's performance as well as how to control the morphology of the active layer.This thesis focuses on a molecular understanding of the morphology formation in a thin film of a polymer blend for OPVs. By using Hansen solubility parameters (HSP) and solution chemistry, the thermodynamics of the phase separation of conjugated polymers, both in solution and thin films, is investigated. Furthermore, to get a deeper understanding of the phase separation between the polymers in the active layer, films were prepared under microgravity conditions, as the phase separation is slowed down under such conditions. Atomic force microscopy combined with infrared spectroscopy was used to characterize the morphology of the dry film.Our results show that understanding solvent-solute and solute-solute interactions is key to comprehending morphology formation. Moreover, HSP proves to be a valuable tool for the initial screening of alternative solvents and solvent blends for more environmentally friendly processing and upscaling. It was found that microgravity conditions provide a tool to study the early stages of phase separation, as well as facilitate the study of the dependence of the morphology on the thicknesses of the film. Additional research is needed to separate the complex effects of gravity fluctuations and to eliminate uncertainty concerning the complete drying of the film under the microgravity phase.
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| 7. |
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| 8. |
- Liu, Yanfeng, et al.
(författare)
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In Situ Optical Spectroscopy Demonstrates the Effect of Solvent Additive in the Formation of All-Polymer Solar Cells
- 2022
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:50, s. 11696-11702
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Tidskriftsartikel (refereegranskat)abstract
- 1-Chloronaphthalene (CN) has been a common solvent additive in both fullerene- A nd nonfullerene-based organic solar cells. In spite of this, its working mechanism is seldom investigated, in particular, during the drying process of bulk heterojunctions composed of a donor:acceptor mixture. In this work, the role of CN in all-polymer solar cells is investigated by in situ spectroscopies and ex situ characterization of blade-coated PBDB-T:PF5-Y5 blends. Our results suggest that the added CN promotes self-aggregation of polymer donor PBDB-T during the drying process of the blend film, resulting in enhanced crystallinity and hole mobility, which contribute to the increased fill factor and improved performance of PBDB-T:PF5-Y5 solar cells. Besides, the nonradiative energy loss of the corresponding device is also reduced by the addition of CN, corresponding to a slightly increased open-circuit voltage. Overall, our observations deepen our understanding of the drying dynamics, which may guide further development of all-polymer solar cells.
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| 9. |
- Paleti, Sri Harish Kumar, et al.
(författare)
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Hexanary blends : a strategy towards thermally stable organic photovoltaics
- 2023
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Non-fullerene based organic solar cells display a high initial power conversion efficiency but continue to suffer from poor thermal stability, especially in case of devices with thick active layers. Mixing of five structurally similar acceptors with similar electron affinities, and blending with a donor polymer is explored, yielding devices with a power conversion efficiency of up to 17.6%. The hexanary device performance is unaffected by thermal annealing of the bulk-heterojunction active layer for at least 23 days at 130 °C in the dark and an inert atmosphere. Moreover, hexanary blends offer a high degree of thermal stability for an active layer thickness of up to 390 nm, which is advantageous for high-throughput processing of organic solar cells. Here, a generic strategy based on multi-component acceptor mixtures is presented that permits to considerably improve the thermal stability of non-fullerene based devices and thus paves the way for large-area organic solar cells.
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| 10. |
- Su, Wenyan, et al.
(författare)
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Nonconjugated Terpolymer Acceptors with Two Different Fused-Ring Electron-Deficient Building Blocks for Efficient All-Polymer Solar Cells
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:5, s. 6442-6449
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Tidskriftsartikel (refereegranskat)abstract
- The ternary polymerization strategy of incorporating different donor and acceptor units forming terpolymers as photovoltaic materials has been proven advantageous in improving power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Herein, a series of low band gap nonconjugated terpolymer acceptors based on two different fused-ring electron-deficient building blocks (IDIC16 and ITIC) with adjustable photoelectric properties were developed. As the third component, ITIC building blocks with a larger pi-conjugation structure, shorter solubilizing side chains, and red-shifted absorption spectrum were incorporated into an IDIC16-based nonconjugated copolymer acceptor PF1-TS4, which built up the terpolymers with two conjugated building blocks linked by flexible thioalkyl chain-thiophene segments. With the increasing ITIC content, terpolymers show gradually broadened absorption spectra and slightly down-shifted lowest unoccupied molecular orbital levels. The active layer based on terpolymer PF1-TS4-60 with a 60% ITIC unit presents more balanced hole and electron mobilities, higher photoluminescence quenching efficiency, and improved morphology compared to those based on PF1-TS4. In all-polymer solar cells (all-PSCs), PF1-TS4-60, matched with a wide band gap polymer donor PM6, achieved a similar open-circuit voltage (V-oc) of 0.99 V, a dramatically increased short-circuit current density (J(sc)) of 15.30 mA cm(-2), and fill factor (FF) of 61.4% compared to PF1-TS4 = 0.99 V, J(sc) = 11.21 mA cm(-2), and FF = 55.6%). As a result, the PF1-TS4-60-based all-PSCs achieved a PCE of 9.31%, which is similar to 50% higher than the PF1-TS4-based ones (6.17%). The results demonstrate a promising approach to develop high-performance nonconjugated terpolymer acceptors for efficient all-PSCs by means of ternary polymerization using two different A-D-A-structured fused-ring electron-deficient building blocks.
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