| 1. |
- Craighero, Mariavittoria, 1995, et al.
(författare)
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Impact of Oligoether Side-Chain Length on the Thermoelectric Properties of a Polar Polythiophene
- 2024
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Ingår i: ACS Applied Electronic Materials. - : AMER CHEMICAL SOC. - 2637-6113. ; 6:5, s. 2909-2916
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Forskningsöversikt (refereegranskat)abstract
- Conjugated polymers with oligoether side chains make up a promising class of thermoelectric materials. In this work, the impact of the side-chain length on the thermoelectric and mechanical properties of polythiophenes is investigated. Polymers with tri-, tetra-, or hexaethylene glycol side chains are compared, and the shortest length is found to result in thin films with the highest degree of order upon doping with the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ). As a result, a stiff material with an electrical conductivity of up to 830 +/- 15 S cm(-1) is obtained, resulting in a thermoelectric power factor of about 21 mu W m(-1) K-2 in the case of as-cast films. Aging at ambient conditions results in an initial decrease in thermoelectric properties but then yields a highly stable performance for at least 3 months, with values of about 200 S cm(-1) and 5 mu W m(-1) K-2. Evidently, identification of the optimal side-chain length is an important criterion for the design of conjugated polymers for organic thermoelectrics.
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| 2. |
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| 3. |
- 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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| 4. |
- Marina, Sara, et al.
(författare)
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Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene
- 2021
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 31:29
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Tidskriftsartikel (refereegranskat)abstract
- Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the pi-pi stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable-or even higher-charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.
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| 5. |
- Müller, Christian, et al.
(författare)
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Determination of Thermal Transition Depth Profiles in Polymer Semiconductor Films with Ellipsometry
- 2013
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 46:18, s. 7325-7331
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Tidskriftsartikel (refereegranskat)abstract
- Geometric confinement and interface effects can significantly alter the thermodynamic properties of thin polymer films. Phase transition temperatures have been shown to strongly depend on film thickness below a critical thickness threshold. It has been suggested that this behavior is due to an interface-induced continuous variation in phase transition 200 temperatures throughout the depth of the films. Here we employ variable-temperature spectroscopic ellipsometry to demonstrate the existence of these depth profiles. We examine four different polymer semiconductors that are of interest for organic light-emitting diodes, solar cells, and field-effect transistors. In contrast to insulating polymers, these light-absorbing materials provide detailed information about structural changes as a function of depth due to wavelength-dependent attenuation. This concept enables us to investigate a broad range of thermodynamic processes including the glass transition, crystallization as well as crystalline and liquid-crystalline melting. In general, for the here investigated systems, higher transition temperatures are found at the free surface. Finally, the deduced profiles are used to predict the thickness dependence of the mean phase transition temperature.
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| 6. |
- Müller, Christian, et al.
(författare)
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Phase behaviour of liquid-crystalline polymer/fullerene organic photovoltaic blends : thermal stability and miscibility
- 2011
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Ingår i: Journal of Materials Chemistry. - : RSC Publishing. - 0959-9428 .- 1364-5501. ; 21, s. 10676-10684
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Tidskriftsartikel (refereegranskat)abstract
- The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquidcrystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variabletemperature ellipsometry complemented by photo- and electroluminescence spectroscopy as well as optical microscopy and scanning force nanoscopy to explore phase transitions of blend thin films. The high glass transition temperature correlates with the good thermal stability of solar cells based on these materials. Furthermore, we observe partial miscibility of the donor and acceptor together with the tendency of excess fullerene derivative to segregate into exceedingly large domains. Thus, for charge generation less adequate bulk-heterojunction nanostructures are poised to develop if this mixture is exposed to more elevated temperatures. Gratifyingly, the solubility of the fullerene derivative in the polymer phase is found to decrease if a higher molecular-weight polymer fraction is employed, which offers routes towards improving the photovoltaic performance of non-crystalline OPV blends.
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| 7. |
- Rodriguez Martinez, Xabier, et al.
(författare)
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Laminated Organic Photovoltaic Modules for Agrivoltaics and Beyond: An Outdoor Stability Study of All-Polymer and Polymer:Small Molecule Blends
- 2023
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 33:10
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Tidskriftsartikel (refereegranskat)abstract
- The integration of organic photovoltaic (OPV) modules on greenhouses is an encouraging practice to offset the energy demands of crop growth and provide extra functionality to dedicated farmland. Nevertheless, such OPV devices must meet certain optical and stability requirements to turn net zero energy greenhouse systems a reality. Here a donor:acceptor polymer blend is optimized for its use in laminated devices while matching the optical needs of crops. Optical modeling is performed and a greenhouse figure-of-merit is introduced to benchmark the trade-off between photovoltaic performance and transparency for both chloroplasts and humans. Balanced donor:acceptor ratios result in better-performing and more thermally stable devices than acceptor-enriched counterparts. The optimized polymer blend and state-of-the-art polymer:small-molecule blends are next transferred to 25 cm(2) laminated modules processed entirely from solution and in ambient conditions. The modules are mounted on a greenhouse as standalone or 4-terminal tandem configurations and their outdoor stability is tracked for months. The study reveals degradation modes undetectable under laboratory conditions such as module delamination, which accounts for 10-20% loss in active area. Among the active layers tested, polymer:fullerene blends are the most stable and position as robust light harvesters in future building-integrated OPV systems.
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| 8. |
- Rodriguez Martinez, Xabier, et al.
(författare)
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Matching electron transport layers with a non-halogenated and low synthetic complexity polymer:fullerene blend for efficient outdoor and indoor organic photovoltaics
- 2022
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 10:19, s. 10768-10779
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Tidskriftsartikel (refereegranskat)abstract
- The desired attributes of organic photovoltaics (OPV) as a low cost and sustainable energy harvesting technology demand the use of non-halogenated solvent processing for the photoactive layer (PAL) materials, preferably of low synthetic complexity (SC) and without compromising the power conversion efficiency (PCE). Despite their record PCEs, most donor-acceptor conjugated copolymers in combination with non-fullerene acceptors are still far from upscaling due to their high cost and SC. Here we present a non-halogenated and low SC ink formulation for the PAL of organic solar cells, comprising PTQ10 and PC61BM as donor and acceptor materials, respectively, showing a record PCE of 7.5% in blade coated devices under 1 sun, and 19.9% under indoor LED conditions. We further study the compatibility of the PAL with 5 different electron transport layers (ETLs) in inverted architecture. We identify that commercial ZnO-based formulations together with a methanol-based polyethyleneimine-Zn (PEI-Zn) chelated ETL ink are the most suitable interlayers for outdoor conditions, providing fill factors as high as 74% and excellent thickness tolerance (up to 150 nm for the ETL, and >200 nm for the PAL). In indoor environments, SnO2 shows superior performance as it does not require UV photoactivation. Semi-transparent devices manufactured entirely in air via lamination show indoor PCEs exceeding 10% while retaining more than 80% of the initial performance after 400 and 350 hours of thermal and light stress, respectively. As a result, PTQ10:PC61BM combined with either PEI-Zn or SnO2 is currently positioned as a promising system for industrialisation of low cost, multipurpose OPV modules.
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| 9. |
- Rodriguez-Martinez, Xabier, et al.
(författare)
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Microfluidic-Assisted Blade Coating of Compositional Libraries for Combinatorial Applications: The Case of Organic Photovoltaics
- 2020
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 10:33
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Tidskriftsartikel (refereegranskat)abstract
- Microfluidic technologies are highly adept at generating controllable compositional gradients in fluids, a feature that has accelerated the understanding of the importance of chemical gradients in biological processes. That said, the development of versatile methods to generate controllable compositional gradients in the solid-state has been far more elusive. The ability to produce such gradients would provide access to extensive compositional libraries, thus enabling the high-throughput exploration of the parametric landscape of functional solids and devices in a resource-, time-, and cost-efficient manner. Herein, the synergic integration of microfluidic technologies is reported with blade coating to enable the controlled formation of compositional lateral gradients in solution. Subsequently, the transformation of liquid-based compositional gradients into solid-state thin films using this method is demonstrated. To demonstrate efficacy of the approach, microfluidic-assisted blade coating is used to optimize blending ratios in organic solar cells. Importantly, this novel technology can be easily extended to other solution processable systems that require the formation of solid-state compositional lateral gradients.
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| 10. |
- Yan, Jun, et al.
(författare)
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Identifying structure-absorption relationships and predicting absorption strength of non-fullerene acceptors for organic photovoltaics
- 2022
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Ingår i: Energy & Environmental Science. - : ROYAL SOC CHEMISTRY. - 1754-5692 .- 1754-5706. ; 15:7, s. 2958-2973
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Tidskriftsartikel (refereegranskat)abstract
- Non-fullerene acceptors (NFAs) are excellent light harvesters, yet the origin of their high optical extinction is not well understood. In this work, we investigate the absorption strength of NFAs by building a database of time-dependent density functional theory (TDDFT) calculations of similar to 500 pi-conjugated molecules. The calculations are first validated by comparison with experimental measurements in solution and solid state using common fullerene and non-fullerene acceptors. We find that the molar extinction coefficient (epsilon(d,max)) shows reasonable agreement between calculation in vacuum and experiment for molecules in solution, highlighting the effectiveness of TDDFT for predicting optical properties of organic pi-conjugated molecules. We then perform a statistical analysis based on molecular descriptors to identify which features are important in defining the absorption strength. This allows us to identify structural features that are correlated with high absorption strength in NFAs and could be used to guide molecular design: highly absorbing NFAs should possess a planar, linear, and fully conjugated molecular backbone with highly polarisable heteroatoms. We then exploit a random decision forest algorithm to draw predictions for epsilon(d,max) using a computational framework based on extended tight-binding Hamiltonians, which shows reasonable predicting accuracy with lower computational cost than TDDFT. This work provides a general understanding of the relationship between molecular structure and absorption strength in pi-conjugated organic molecules, including NFAs, while introducing predictive machine-learning models of low computational cost.
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