| 1. |
- Almora, Osbel, et al.
(författare)
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Device Performance of Emerging Photovoltaic Materials (Version 1)
- 2020
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye-sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi-junction PVs. Nevertheless, it can be very time consuming to find or develop an up-to-date overview of the state-of-the-art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state-of-the-art emerging PVs.
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| 2. |
- Broekman, Maarten J. E., et al.
(författare)
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Evaluating expert-based habitat suitability information of terrestrial mammals with GPS-tracking data
- 2022
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 31:8, s. 1526-1541
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Tidskriftsartikel (refereegranskat)abstract
- Aim: Macroecological studies that require habitat suitability data for many species often derive this information from expert opinion. However, expert-based information is inherently subjective and thus prone to errors. The increasing availability of GPS tracking data offers opportunities to evaluate and supplement expert-based information with detailed empirical evidence. Here, we compared expert-based habitat suitability information from the International Union for Conservation of Nature (IUCN) with habitat suitability information derived from GPS-tracking data of 1,498 individuals from 49 mammal species.Location: Worldwide.Time period: 1998-2021.Major taxa studied: Forty-nine terrestrial mammal species.Methods: Using GPS data, we estimated two measures of habitat suitability for each individual animal: proportional habitat use (proportion of GPS locations within a habitat type), and selection ratio (habitat use relative to its availability). For each individual we then evaluated whether the GPS-based habitat suitability measures were in agreement with the IUCN data. To that end, we calculated the probability that the ranking of empirical habitat suitability measures was in agreement with IUCN's classification into suitable, marginal and unsuitable habitat types.Results: IUCN habitat suitability data were in accordance with the GPS data (> 95% probability of agreement) for 33 out of 49 species based on proportional habitat use estimates and for 25 out of 49 species based on selection ratios. In addition, 37 and 34 species had a > 50% probability of agreement based on proportional habitat use and selection ratios, respectively.Main conclusions: We show how GPS-tracking data can be used to evaluate IUCN habitat suitability data. Our findings indicate that for the majority of species included in this study, it is appropriate to use IUCN habitat suitability data in macroecological studies. Furthermore, we show that GPS-tracking data can be used to identify and prioritize species and habitat types for re-evaluation of IUCN habitat suitability data.
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| 3. |
- Charrier, Dimitri S. H., et al.
(författare)
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Large Electrically Induced Height and Volume Changes in Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) Thin Films
- 2010
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Ingår i: Chemistry of Materials. - : American Chemical Society. - 0897-4756 .- 1520-5002. ; 22:12, s. 3670-3677
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate large, partly reversible height and volume changes of thin films of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) on the anode of interdigitating gold electrodes under ambient conditions by applying an electrical bias. The height and volume changes were monitored with optical and atomic force microscopy and are found to be independent of initial film thickness. In the first cycle, a relative height change of 950% is observed for a 21 nm thick film. Two regimes are identified. In the first regime, reversible redox reactions occur and reversible height changes can be ascribed to absorption of water via osmotic effects, brought about by an increasing ion concentration on the anode. In the second, irreversible regime, irreversible overoxidation of the PEDOT occurs and mass transport from the channel to the anode becomes important.
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| 4. |
- Charrier, Dimitri S. H., et al.
(författare)
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Real versus measured surface potentials in scanning Kelvin probe microscopy
- 2008
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 2:4, s. 622-626
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Tidskriftsartikel (refereegranskat)abstract
- Noncontact potentiometry or scanning Kelvin probe microscopy (SKPM) is a widely used technique to study charge injection and transport in (in)organic devices by measuring a laterally resolved local potential. This technique suffers from the significant drawback that experimentally obtained curves do not generally reflect the true potential profile in the device due to nonlocal coupling between the probing tip and the device. In this work, we quantitatively explain the experimental SKPM response and by doing so directly link theoretical device models to real observables. In particular, the model quantitatively explains the effects of the tip-sample distance and the dependence on the orientation of the probing tip with respect to the device.
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| 5. |
- Chr Germs, Wijnand, et al.
(författare)
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High-efficiency dielectrophoretic ratchet
- 2012
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- Brownian ratchets enable the use of thermal motion in performing useful work. They typically employ spatial asymmetry to rectify nondirected external forces that drive the system out of equilibrium (cf. running marbles on a shaking washboard). The major application foreseen for Brownian ratchets is high-selectivity fractionation of particle or molecule distributions. Here, we investigate the functioning of an important model system, the on/off ratchet forwater-suspended particles, in which interdigitated finger electrodes can be switched on and off to create a time-dependent, spatially periodic but asymmetric potential. Surprisingly, we find that mainly dielectrophoretic rather than electrophoretic forces are responsible for the ratchet effect. This has major implications for the (a) symmetry of the ratchet potential and the settings needed for optimal performance. We demonstrate that by applying a potential offset the ratchet can be optimized such that its particle displacement efficiency reaches the theoretical upper limit corresponding to the electrode geometry and particle size. Efficient fractionation based on size selectivity is therefore not only possible for charged species, but also for uncharged ones, which greatly expands the applicability range of this type of Brownian ratchet.
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| 6. |
- Christian Roelofs, W. S., et al.
(författare)
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Fundamental Limitations for Electroluminescence in Organic Dual-Gate Field-Effect Transistors
- 2014
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 26:26, s. 4450-
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Tidskriftsartikel (refereegranskat)abstract
- A dual-gate organic field-effect transistor is investigated for electrically pumped lasing. The two gates can independently accumulate electrons and holes, yielding current densities exceeding the lasing threshold. Here, the aim is to force the electrons and holes to recombine by confining the charges in a single semiconducting film. It is found that independent hole and electron accumulation is mutually exclusive with vertical recombination and light emission.
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| 7. |
- Christian Roelofs, W. S., et al.
(författare)
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Light Emission in the Unipolar Regime of Ambipolar Organic Field-Effect Transistors
- 2013
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 23:33, s. 4133-4139
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Tidskriftsartikel (refereegranskat)abstract
- Light emission from ambipolar organic field-effect transistors (OFETs) is often observed when they are operated in the unipolar regime. This is unexpected, the light emission should be completely suppressed, because in the unipolar regime only one type of charge carrier is accumulated. Here, an electroluminescent diketopyrrolopyrrole copolymer is investigated. Local potential measurements by scanning Kelvin probe microscopy reveal a recombination position that is unstable in time due to the presence of injection barriers. The electroluminescence and electrical transport have been numerically analyzed. It is shown that the counterintuitive unipolar light emission is quantitatively explained by injection of minority carriers into deep tail states of the semiconductor. The density of the injected minority carriers is small. Hence they are relatively immobile and they recombine close the contact with accumulated majority carriers. The unipolar light output is characterized by a constant efficiency independent of gate bias. It is argued that light emission from OFETs predominantly originates from the unipolar regime when the charge transport is injection limited.
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| 8. |
- Di Nuzzo, Daniele, et al.
(författare)
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Evidence for space-charge-limited conduction in organic photovoltaic cells at open-circuit conditions
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:8
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Tidskriftsartikel (refereegranskat)abstract
- The ac admittance of solar cells under illumination is investigated under open-circuit conditions. Open-circuit conditions are imposed by inserting a probe capacitor into the circuit. The capacitance and conductance of the cells are investigated as function of frequency and continuous illumination intensity. Results are compared with numerical and analytical modeling of charge recombination and transport. In bulk heterojunction solar cells with [6,6]-Phenyl-C-61(C-71)-butyric acid methyl ester as acceptor and poly(3-hexylthiophene) or poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylene vinylene] as electron donor, the high-frequency capacitance C and conductance G follow a power-law dependence on intensity of white light I, with G(I) proportional to I-3/4 and C(I) proportional to I-1/4. The modeling shows that these dependencies can be explained in terms of space-charge-limited current in combination with Langevin type recombination of carriers. For poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b]dithiophene-2,6-diyl]] the capacitance shows a weaker dependence on intensity, indicating fast recombination of photogenerated carriers. Results indicate that the fill factor of relatively well performing polymer solar cells can still be limited by space charge effects and can be improved by enhancing the charge carrier mobility or by reducing the bimolecular Langevin recombination. DOI: 10.1103/PhysRevB.87.085207
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| 9. |
- Duan, Chunhui, et al.
(författare)
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Improving Performance of All-Polymer Solar Cells Through Backbone Engineering of Both Donors and Acceptors
- 2018
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 2:12
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Tidskriftsartikel (refereegranskat)abstract
- All-polymer solar cells (APSCs), composed of semiconducting donor and acceptor polymers, have attracted considerable attention due to their unique advantages compared to polymer-fullerene-based devices in terms of enhanced light absorption and morphological stability. To improve the performance of APSCs, the morphology of the active layer must be optimized. By employing a random copolymerization strategy to control the regularity of the backbone of the donor polymers (PTAZ-TPDx) and acceptor polymers (PNDI-Tx) the morphology can be systematically optimized by tuning the polymer packing and crystallinity. To minimize effects of molecular weight, both donor and acceptor polymers have number-average molecular weights in narrow ranges. Experimental and coarse-grained modeling results disclose that systematic backbone engineering greatly affects the polymer crystallinity and ultimately the phase separation and morphology of the all-polymer blends. Decreasing the backbone regularity of either the donor or the acceptor polymer reduces the local crystallinity of the individual phase in blend films, affording reduced short-circuit current densities and fill factors. This two-dimensional crystallinity optimization strategy locates a PCE maximum at highest crystallinity for both donor and acceptor polymers. Overall, this study demonstrates that proper control of both donor and acceptor polymer crystallinity simultaneously is essential to optimize APSC performance.
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| 10. |
- Feng, Guitao, et al.
(författare)
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“Double-Cable” Conjugated Polymers with Linear Backbone toward High Quantum Efficiencies in Single-Component Polymer Solar Cells
- 2017
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 139:51, s. 18647-18656
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Tidskriftsartikel (refereegranskat)abstract
- A series of "double-cable" conjugated polymers were developed for application in efficient single-component polymer solar cells, in which high quantum efficiencies could be achieved due to the optimized nanophase separation between donor and acceptor parts. The new double-cable polymers contain electron-donating poly(benzodithiophene) (BDT) as linear conjugated backbone for hole transport and pendant electron-deficient perylene bisimide (PBI) units for electron transport, connected via a dodecyl linker. Sulfur and fluorine substituents were introduced to tune the energy levels and crystallinity of the conjugated polymers. The double-cable polymers adopt a "face-on" orientation in which the conjugated BDT backbone and the pendant PBI units have a preferential pi-pi stacking direction perpendicular to the substrate, favorable for interchain charge transport normal to the plane. The linear conjugated backbone acts as a scaffold for the crystallization of the PBI groups, to provide a double-cable nanophase separation of donor and acceptor phases. The optimized nanophase separation enables efficient exciton dissociation as well as charge transport as evidenced from the high-up to 80%-internal quantum efficiency for photon-to-electron conversion. In single-component organic solar cells, the double-cable polymers provide power conversion efficiency up to 4.18%. This is one of the highest performances in single-component organic solar cells. The nanophase-separated design can likely be used to achieve high-performance single-component organic solar cells.
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| 11. |
- Gauld, Jethro G., et al.
(författare)
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Hotspots in the grid : Avian sensitivity and vulnerability to collision risk from energy infrastructure interactions in Europe and North Africa
- 2022
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Ingår i: Journal of Applied Ecology. - : John Wiley & Sons. - 0021-8901 .- 1365-2664. ; 59:6, s. 1496-1512
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Tidskriftsartikel (refereegranskat)abstract
- Wind turbines and power lines can cause bird mortality due to collision or electrocution. The biodiversity impacts of energy infrastructure (EI) can be minimised through effective landscape-scale planning and mitigation. The identification of high-vulnerability areas is urgently needed to assess potential cumulative impacts of EI while supporting the transition to zero carbon energy. We collected GPS location data from 1,454 birds from 27 species susceptible to collision within Europe and North Africa and identified areas where tracked birds are most at risk of colliding with existing EI. Sensitivity to EI development was estimated for wind turbines and power lines by calculating the proportion of GPS flight locations at heights where birds were at risk of collision and accounting for species' specific susceptibility to collision. We mapped the maximum collision sensitivity value obtained across all species, in each 5 x 5 km grid cell, across Europe and North Africa. Vulnerability to collision was obtained by overlaying the sensitivity surfaces with density of wind turbines and transmission power lines. Results: Exposure to risk varied across the 27 species, with some species flying consistently at heights where they risk collision. For areas with sufficient tracking data within Europe and North Africa, 13.6% of the area was classified as high sensitivity to wind turbines and 9.4% was classified as high sensitivity to transmission power lines. Sensitive areas were concentrated within important migratory corridors and along coastlines. Hotspots of vulnerability to collision with wind turbines and transmission power lines (2018 data) were scattered across the study region with highest concentrations occurring in central Europe, near the strait of Gibraltar and the Bosporus in Turkey. Synthesis and applications. We identify the areas of Europe and North Africa that are most sensitive for the specific populations of birds for which sufficient GPS tracking data at high spatial resolution were available. We also map vulnerability hotspots where mitigation at existing EI should be prioritised to reduce collision risks. As tracking data availability improves our method could be applied to more species and areas to help reduce bird-EI conflicts.
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| 12. |
- Hansson, Rickard, 1987-
(författare)
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Materials and Device Engineering for Efficient and Stable Polymer Solar Cells
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer solar cells form a promising technology for converting sunlight into electricity, and have reached record efficiencies over 10% and lifetimes of several years. The performance of polymer solar cells depends strongly on the distribution of electron donor and acceptor materials in the active layer. To achieve longer lifetimes, degradation processes in the materials have to be understood. In this thesis, a set of complementary spectroscopy and microscopy techniques, among which soft X-ray techniques have been used to determine the morphology of polymer:fullerene based active layers. We have found that the morphology of TQ1:PC70BM films is strongly influenced by the processing solvent and the use of solvent additives. We have also found, by using soft X-ray techniques, that not only the light-absorbing polymer TQ1, but also the fullerene is susceptible to photo-degradation in air. Moreover, the fullerene degradation is accelerated in the presence of the polymer. Additionally, this thesis addresses the role of the interfacial layers for device performance and stability. The commonly used hole transport material PEDOT:PSS has the advantage of being solution processable at room temperature, but this layer is also known to contribute to the device degradation. We have found that low-temperature processed NiOx is a promising alternative to PEDOT:PSS, leading to improved device performance. Even for encapsulated polymer solar cells, some photo-induced degradation of the electrical performance is observed and is found to depend on the nature of the hole transport material. We found a better initial stability for solar cells with MoO3 hole transport layers than with PEDOT:PSS. In the pursuit of understanding the initial decrease in electrical performance of PEDOT:PSS-based devices, simulations were performed, from which a number of degradation sources could be excluded.
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| 13. |
- Jan Anton Koster, L., et al.
(författare)
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Quantifying Bimolecular Recombination Losses in Organic Bulk Heterojunction Solar Cells
- 2011
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 23:14, s. 1670-
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Tidskriftsartikel (refereegranskat)abstract
- We present a new experimental technique that affords direct quantification of the fraction of charge carriers lost in poly(3-hexylthiophene): fullerene solar cells by bimolecular recombination. Depending on annealing conditions up to 17% of carriers recombine bimolecularly under solar illumination. We explain our findings with a closed analytical expression for the photocurrent generated by an organic solar cell.
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| 14. |
- Janssen, Annette B. G., et al.
(författare)
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Exploring, exploiting and evolving diversity of aquatic ecosystem models : a community perspective
- 2015
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Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 49:4, s. 513-548
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Tidskriftsartikel (refereegranskat)abstract
- Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5-10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary.
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| 15. |
- Janssen, Rene, et al.
(författare)
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Machine Learning Predicts the Presence of 2,4,6-Trinitrotoluene in Sediments of a Baltic Sea Munitions Dumpsite Using Microbial Community Compositions
- 2021
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria are ubiquitous and live in complex microbial communities. Due to differences in physiological properties and niche preferences among community members, microbial communities respond in specific ways to environmental drivers, potentially resulting in distinct microbial fingerprints for a given environmental state. As proof of the principle, our goal was to assess the opportunities and limitations of machine learning to detect microbial fingerprints indicating the presence of the munition compound 2,4,6-trinitrotoluene (TNT) in southwestern Baltic Sea sediments. Over 40 environmental variables including grain size distribution, elemental composition, and concentration of munition compounds (mostly at pmol.g(-1) levels) from 150 sediments collected at the near-to-shore munition dumpsite Kolberger Heide by the German city of Kiel were combined with 16S rRNA gene amplicon sequencing libraries. Prediction was achieved using Random Forests (RFs); the robustness of predictions was validated using Artificial Neural Networks (ANN). To facilitate machine learning with microbiome data we developed the R package phyloseq2ML. Using the most classification-relevant 25 bacterial genera exclusively, potentially representing a TNT-indicative fingerprint, TNT was predicted correctly with up to 81.5% balanced accuracy. False positive classifications indicated that this approach also has the potential to identify samples where the original TNT contamination was no longer detectable. The fact that TNT presence was not among the main drivers of the microbial community composition demonstrates the sensitivity of the approach. Moreover, environmental variables resulted in poorer prediction rates than using microbial fingerprints. Our results suggest that microbial communities can predict even minor influencing factors in complex environments, demonstrating the potential of this approach for the discovery of contamination events over an integrated period of time. Proven for a distinct environment future studies should assess the ability of this approach for environmental monitoring in general.
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| 16. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
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3D-Morphology Reconstruction of Nanoscale Phase-Separation in Polymer Memory Blends
- 2015
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Ingår i: Journal of Polymer Science Part B. - : John Wiley & Sons. - 0887-6266 .- 1099-0488. ; 53:17, s. 1231-1237
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Tidskriftsartikel (refereegranskat)abstract
- In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase-separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. (c) 2015 Wiley Periodicals, Inc.
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| 17. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
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Data retention in organic ferroelectric resistive switches
- 2016
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 31, s. 56-62
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organic ferroelectric resistive switches could become the long-missing non-volatile memory elements in organic electronic devices. To this end, data retention in these devices should be characterized, understood and controlled. First, it is shown that the measurement protocol can strongly affect the apparent retention time and a suitable protocol is identified. Second, it is shown by experimental and theoretical methods that partial depolarization of the ferroelectric is the major mechanism responsible for imperfect data retention. This depolarization occurs in close vicinity to the semiconductor-ferroelectric interface, is driven by energy minimization and is inherently present in this type of phase-separated polymer blends. Third, a direct relation between data retention and the charge injection barrier height of the resistive switch is demonstrated experimentally and numerically. Tuning the injection barrier height allows to improve retention by many orders of magnitude in time, albeit at the cost of a reduced on/off ratio. (c) 2016 Elsevier B.V. All rights reserved.
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| 18. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
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Multi-bit organic ferroelectric memory
- 2013
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 14:12, s. 3399-3405
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Tidskriftsartikel (refereegranskat)abstract
- Storage of multiple bits per element is a promising alternative to miniaturization for increasing the information data density in memories. Here we introduce a multi-bit organic ferroelectric-based non-volatile memory with binary readout from a simple capacitor structure. The functioning of our multi-bit concept is quite generally applicable and depends on the following properties for the data storage medium: (a) The data storage medium effectively consists of microscopic switching elements (hysterons). (b) The positive and negative coercive fields of each hysteron are equal in magnitude. (c) The distribution of hysteron coercive fields has substantial width. We show that the organic ferroelectric copolymer P(VDF-TrFE) meets these requirements. All basic properties of our device were measured and modeled in the framework of the dipole switching theory (DST). As a first example we show the possibility to independently program and subsequently read out the lower, middle and upper parts of the hysteron distribution function, yielding a 3-bit memory in a single capacitor structure. All measured devices show good state reproducibility, high endurance and potentially great scalability.
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| 19. |
- Khikhlovskyi, Vsevolod, et al.
(författare)
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Nanoscale Organic Ferroelectric Resistive Switches
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:6, s. 3305-3312
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Tidskriftsartikel (refereegranskat)abstract
- Organic ferroelectric resistive switches function by grace of nanoscale phase separation in a blend of a semiconducting and a ferroelectric polymer that is sandwiched between metallic electrodes. In this work, various scanning probe techniques are combined with numerical modeling to unravel their operational mechanism. Resistive switching is shown to result from modulation of the charge injection barrier at the semiconductor-electrode interfaces. The modulation is driven by the stray field of the polarization charges in the ferroelectric phase and consequently is restricted to regions where semiconductor and ferroelectric phases exist in close vicinity. Since each semiconductor domain can individually be switched and read out, a novel, nanoscale memory element is demonstrated. An ultimate information density of similar to 30 Mb/cm(2) is estimated for this bottom-up defined memory device.
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| 20. |
- Krebs, Frederik C, et al.
(författare)
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A round robin study of flexible large-area roll-to-roll processed polymer solar cell modules
- 2009
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Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - : Elsevier BV. - 0927-0248. ; 93:11, s. 1968-1977
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Tidskriftsartikel (refereegranskat)abstract
- A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Riso DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Riso DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths.
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| 21. |
- Lakhwani, Girish, et al.
(författare)
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Intensive Chiroptical Properties of Chiral Polyfluorenes Associated with Fibril Formation
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 113:43, s. 14047-14051
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of chiral poly {9,9-bis[(3S)-3,7-dimethyloctyl]-2,7-fluorene} (1) were studied using circular dichroism (CD) spectroscopy. Films spin coated from chloroform solution, show CD with a degree of polarization g(abs) (= +4 x 10(-4) at 400 nm) that is independent of film thickness (50-290 nm). This implies that gabs is an intensive property of the material and related to the chiral organization of the molecules on a length scale less than 50 nm. Atomic force microscopy (AFM) on the films reveals fibrils. Addition of nonsolvent methanol to a solution of 1 in chloroform leads to fibril formation in solution and results in CD similar in band shape to that of the pristine spin coated films from chloroform solution and a g(abs) comparable in magnitude. Thus the chiral molecular arrangement leading to circular dichroism is part of the internal structure of these fibrils.
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| 22. |
- Larsen, Christian, 1983-
(författare)
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Fabricating designed fullerene nanostructures for functional electronic devices
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A long-term goal within the field of organic electronics has been to developflexible and functional devices, which can be processed and patterned withlow-cost and energy-efficient solution-based methods. This thesis presents anumber of functional paths towards the attainment of this goal via thedevelopment and demonstration of novel fabrication and patterningmethods involving the important organic-semiconductor family termedfullerenes.Fullerenes are soccer-shaped small molecules, with two often-employedexamples being the symmetric C60 molecule and its more soluble derivative[6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We show that PCBM canbe photochemically transformed into a dimeric state in a bi-excited reactionprocess, and that the exposed material features a significantly reducedsolubility in common solvents as well as an effectively retained electronmobility. This attractive combination of material properties allows for adirect and resist-free lithographic patterning of electronic PCBM films downto a smallest feature size of 1 µm, using a simple and scalable two-stepprocess constituting light exposure and solution development. In a furtherdevelopment, it was shown that the two-step method was useful also in thearea-selective transformation of fullerene/conjugated-polymer blend films,as demonstrated through the realization of a functional complementary logiccircuit comprising a 5-stage ring oscillator.In another project, we have synthesized highly flexible, single-crystal C60nanorods with a solution-based self-assembly process termed liquid-liquidinterfacial precipitation. The 1-dimensional nanorods can be deposited fromtheir synthesis solution and employed as the active material in field-effecttransistor devices. Here, it was revealed that the as-fabricated nanorods canfeature an impressive electron mobility of 1.0 cm2 V-1 s-1, which is on par withthe performance of a work horse in the transistor field, viz. vacuumdeposited amorphous Si. We further demonstrated that the processability ofthe nanorods can be improved by a tuned light-exposure treatment, duringwhich the nanorod shell is polymerized while the high-mobility interior bulkis left intact. This has the desired consequence that stabile nanoroddispersions can be prepared in a wide range of solvents, and we anticipatethat functional electronic devices based on solution-processable nanorodscan be realized in a near future.
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| 23. |
- Lee, Jiyoul, et al.
(författare)
-
Pulse-modulated multilevel data storage in an organic ferroelectric resistive memory diode
- 2016
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6:24407
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate multilevel data storage in organic ferroelectric resistive memory diodes consisting of a phase-separated blend of P(VDF-TrFE) and a semiconducting polymer. The dynamic behaviour of the organic ferroelectric memory diode can be described in terms of the inhomogeneous field mechanism (IFM) model where the ferroelectric components are regarded as an assembly of randomly distributed regions with independent polarisation kinetics governed by a time-dependent local field. This allows us to write and non-destructively read stable multilevel polarisation states in the organic memory diode using controlled programming pulses. The resulting 2-bit data storage per memory element doubles the storage density of the organic ferroelectric resistive memory diode without increasing its technological complexity, thus reducing the cost per bit.
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| 24. |
- Li, Zhaojun, 1989, et al.
(författare)
-
9.0% power conversion efficiency from ternary all-polymer solar cells
- 2017
-
Ingår i: Energy and Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 10:10, s. 2212-2221
-
Tidskriftsartikel (refereegranskat)abstract
- Integration of a third component into a single-junction polymer solar cell (PSC) is regarded as an attractive strategy to enhance the performance of PSCs. Although binary all-polymer solar cells (all-PSCs) have recently emerged with compelling power conversion efficiencies (PCEs), the PCEs of ternary all-PSCs still lag behind those of the state-of-the-art binary all-PSCs, and the advantages of ternary systems are not fully exploited. In this work, we realize high-performance ternary all-PSCs with record-breaking PCEs of 9% and high fill factors (FF) of over 0.7 for both conventional and inverted devices. The improved photovoltaic performance benefits from the synergistic effects of extended absorption, more efficient charge generation, optimal polymer orientations and suppressed recombination losses compared to the binary all-PSCs, as evidenced by a set of experimental techniques. The results provide new insights for developing high-performance ternary all-PSCs by choosing appropriate donor and acceptor polymers to overcome limitations in absorption, by affording good miscibility, and by benefiting from charge and energy transfer mechanisms for efficient charge generation.
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| 25. |
- Li, Zhaojun, 1989, et al.
(författare)
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High-Performance and Stable All-Polymer Solar Cells Using Donor and Acceptor Polymers with Complementary Absorption
- 2017
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 7:14
-
Tidskriftsartikel (refereegranskat)abstract
- To explore the advantages of emerging all-polymer solar cells (all-PSCs), growing efforts have been devoted to developing matched donor and acceptor polymers to outperform fullerene-based PSCs. In this work, a detailed characterization and comparison of all-PSCs using a set of donor and acceptor polymers with both conventional and inverted device structures is performed. A simple method to quantify the actual composition and light harvesting contributions from the individual donor and acceptor is described. Detailed study on the exciton dissociation and charge recombination is carried out by a set of measurements to understand the photocurrent loss. It is unraveled that fine-tuned crystallinity of the acceptor, matched donor and acceptor with complementary absorption and desired energy levels, and device architecture engineering can synergistically boost the performance of all-PSCs. As expected, the PBDTTS-FTAZ:PNDI-T10 all-PSC attains a high and stable power conversion efficiency of 6.9% without obvious efficiency decay in 60 d. This work demonstrates that PNDI-T10 can be a potential alternative acceptor polymer to the widely used acceptor N2200 for high-performance and stable all-PSCs.
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| 26. |
- Li, Zhaojun, 1989, et al.
(författare)
-
High-photovoltage all-polymer solar cells based on a diketopyrrolopyrrole-isoindigo acceptor polymer
- 2017
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 5:23, s. 11693-11700
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we synthesized and characterized two new n-type polymers PTDPP-PyDPP and PIID-PyDPP. The former polymer is composed of pyridine-flanked diketopyrrolopyrrole (PyDPP) and thiophene-flanked diketopyrrolopyrrole (TDPP). The latter polymer consists of PyDPP and isoindigo (IID). PIID-PyDPP exhibits a much higher absorption coefficient compared to the widely used naphthalene diimide (NDI)-based acceptor polymers, and its high-lying LUMO level affords it to achieve a high open-circuit voltage (Voc). As a result, an all-polymer solar cell (all-PSC) fabricated from a high band gap polymer PBDTTS-FTAZ as the donor and PIID-PyDPP as the acceptor attained a high Voc of 1.07 V with a power conversion efficiency (PCE) of 4.2%. So far, it has been one of the highest PCEs recorded from all-PSCs using diketopyrrolopyrrole (DPP)-based acceptors. Gratifyingly, no obvious PCE decay was observed in two weeks, unraveling good stability of the all-PSC. This work demonstrates that the electron-withdrawing PyDPP unit can be a promising building block for new acceptor polymers in all-PSCs.
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| 27. |
- Mantovani Nardes, Alexandre, et al.
(författare)
-
A morphological model for the solvent-enhanced conductivity of PEDOT : PSS thin films
- 2008
-
Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 18:6, s. 865-871
-
Tidskriftsartikel (refereegranskat)abstract
- The well-known enhanced conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films that is obtained by addition of high-boiling solvents like sorbitol to the aqueous dispersion used for film deposition is shown to be associated with a rearrangement of PEDOT-rich clusters into elongated domains, as evidenced from STM and AFM. Consistently, temperature dependent conductivity measurements for sorbitol-treated films reveal that charge transport occurs via quasi ID variable range hopping (VRH), in contrast to 3D VRH for untreated PEDOT:PSS films. The typical hopping distance of 60-90 nm, extracted from the conductivity measurements is consistent with hopping between the 30-40 nm sized grains observed with scanning probe microscopy.
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| 28. |
- Mantovani Nardes, Alexandre, et al.
(författare)
-
Microscopic understanding of the anisotropic conductivity of PEDOT : PSS thin films
- 2007
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 19:9, s. 1196-
-
Tidskriftsartikel (refereegranskat)abstract
- The amsotropic conductivity of thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is correlated to the film morphology as obtained from scanning tunneling and atomic force microscopy images. The material was found to consist of layers of flattened PEDOT-rich particles that are separated by quasi-continuous PSS lamella (see figure).
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| 29. |
- Mathijssen, Simon G. J., et al.
(författare)
-
Charge trapping at the dielectric of organic transistors visualized in real time and space
- 2008
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 20:5, s. 975-
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin probe microscopy demonstrates that water-induced charge trapping at the SiO2 dielectric visualized in real time and space - is responsible for the commonly observed gate-bias-induced threshold-voltage shift in organic field-effect transistors. When a bias is applied to the electrodes, charges are injected onto the SiO2 (see background of the figure). When the contacts are grounded, the charges are released again (foreground picture).
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| 30. |
- Mathijssen, Simon G. J., et al.
(författare)
-
Manipulating the local light emission in organic light-emitting diodes by using patterned self-assembled monolayers
- 2008
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 20:14, s. 2703-
-
Tidskriftsartikel (refereegranskat)abstract
- Patterned organic light-emitting diodes are fabricated by using microcontactDrinted self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission
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| 31. |
- Mathijssen, Simon G. J., et al.
(författare)
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Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors
- 2009
-
Ingår i: Nature Nanotechnology. - : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 4:10, s. 674-680
-
Tidskriftsartikel (refereegranskat)abstract
- The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monalayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.
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| 32. |
- Mathijssen, Simon G. J., et al.
(författare)
-
Revealing Buried Interfaces to Understand the Origins of Threshold Voltage Shifts in Organic Field-Effect Transistors
- 2010
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 22:45, s. 5105-
-
Tidskriftsartikel (refereegranskat)abstract
- The semiconductor of an organic field-effect transistor is stripped with adhesive tape, yielding an exposed gate dielectric, accessible for various characterization techniques. By using scanning Kelvin probe microscopy we reveal that trapped charges after gate bias stress are located at the gate dielectric and not in the semiconductor. Charging of the gate dielectric is confirmed by the fact that the threshold voltage shift remains, when a pristine organic semiconductor is deposited on the exposed gate dielectric of a stressed and delaminated field-effect transistor.
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| 33. |
- Maturova, Klara, et al.
(författare)
-
Connecting Scanning Tunneling Spectroscopy to Device Performance for Polymer: Fullerene Organic Solar Cells
- 2010
-
Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 4:3, s. 1385-1392
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy and spectroscopy have been used to measure the local photovoltaic performance of prototypical polymer:fullerene (MDMO-PPV:PCBM) bulk heterojunction films with similar to 10 nm resolution. Fullerene-rich clusters are found to act as sinks, extracting electrons from a shell layer of a homogeneously mixed polymer:fullerene matrix, surrounding the fullerene cluster. The experimental results were quantitatively modeled with a drift-diffusion model that in first order accounts for the specific morphology. The same model has subsequently been used to calculate performance indicators of macroscopic solar cells as a function of film composition and characteristic size of the phase separation. As such, a first step has been set toward a quantitative correlation between nanoscopic and macroscopic device photovoltaic performance.
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| 34. |
- Maturova, Klara, et al.
(författare)
-
Description of the Morphology Dependent Charge Transport and Performance of Polymer:Fullerene Bulk Heterojunction Solar Cells
- 2011
-
Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 21:2, s. 261-269
-
Tidskriftsartikel (refereegranskat)abstract
- We present a combined numerical charge transport and morphology model to describe the current density-voltage (j-V) characteristics of three different, benchmark polymer: fullerene bulk heterojunction organic solar cells in which the device performance critically depends on the processing conditions or composition of the active layer. We find that an accurate description of the j-V characteristics over a broad bias range can be obtained when the actual complex, three-dimensional (3D) phase separation is represented by a simplified 2D or even 1D description. The morphological device model allows predicting the potential for increasing device performance by further optimizing the morphology. The optimal simplified morphology consists of two, relatively thin alternating vertically oriented slabs, that allow for fast lateral separation of photocreated holes and electrons. This morphology can effectively be described as 1D.
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| 35. |
- Maturova, Klara, et al.
(författare)
-
Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends
- 2009
-
Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 19:9, s. 1379-1386
-
Tidskriftsartikel (refereegranskat)abstract
- Here, correlated AFM and scanning Kelvin probe microscopy measurements with sub-100 nm resolution on the phase-separated active layer of polymer-fullerene (MDMO-PPV:PCBM) bulk heterojunction solar cells in the dark and under illumination are described. Using numerical modeling a fully quantitative explanation for the contrast and shifts of the surface potential in dark and light is provided. Under illumination an excess of photogenerated electrons is present in both the donor and acceptor phases. From the time evolution of the surface potential after switching off the light the contributions of free and trapped electrons can be identified. Based on these measurements the relative 3D energy level shifts of the sample are calculated. Moreover, by comparing devices with fine and coarse phase separation, it is found that the inferior performance of the latter devices is, at least partially, due to poor electron transport.
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| 36. |
- Meng, Xiao, et al.
(författare)
-
Ferroelectric Switching and Electrochemistry of Pyrrole Substituted Trialkylbenzene-1,3,5-Tricarboxamides
- 2017
-
Ingår i: Journal of Polymer Science Part B. - : WILEY. - 0887-6266 .- 1099-0488. ; 55:8, s. 673-683
-
Tidskriftsartikel (refereegranskat)abstract
- We explore a new approach to organic ferroelectric diodes using a benzene-tricarboxamide (BTA) core connected with C10 alkyl chains to pyrrole groups, which can be polymerized to provide a semiconducting ferroelectric material. The compound possesses a columnar hexagonal liquid crystalline (LC) phase and exhibits ferroelectric switching. At low switching frequencies, an additional process occurs, which leads to a high hysteretic charge density of up to similar to 1000 mC/m(2). Based on its slow rate, the formation of gas bubbles, and the emergence of characteristic polypyrrole absorption bands in the UV-Vis-NIR, the additional process is identified as the oxidative polymerization of pyrrole groups, enabled by the presence of amide groups. Polymerization of the pyrrole groups, which is essential to obtain semiconductivity, is limited to thin layers at the electrodes, amounting to similar to 17 nm after cycling for 21 h. (C) 2017 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc.
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| 37. |
- Riccardi, Ludovico, 1993-
(författare)
-
Molecular Copper and Ruthenium Water Oxidation Electrocatalysts for Light-Driven Water Splitting
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, there has been a growing awareness of the need to transition to renewable energy to mitigate the effects of climate change and reduce greenhouse gas emissions. Governments, businesses, and individuals are investing in renewable energy infrastructure and technologies to create a more sustainable energy future. This thesis explores transition metal-based molecular complexes for water oxidation catalysis and their integration into water-splitting devices. Water oxidation (WO) is a key reaction in all processes intended to produce chemical fuels from water. When water splitting is driven by solar light, it is also referred to as artificial photosynthesis.The work focuses on a molecular copper catalyst with a tetra-amidate macrocyclic ligand (TAML), called [CuMac]2−, which can be isolated as a (Me4N)2[CuMac] salt. Derivatives of the organic ligand scaffold bearing either two ester or two carboxylic acid functionalities were synthesized to enable heterogenization of [CuMac]2−. The compounds were evaluated for their oxygen evolution reaction (OER) activity at different operational pH. However, introducing the carboxylic moieties appeared to be kinetically detrimental to the OER activity compared to that of the parent [CuMac]2−. A study on identifying possible short-lived intermediates in the catalytic cycle of [CuMac]2−is presented. UV-visible transient absorption spectroscopy was used to deduce the electron transfer mechanism and kinetics of catalyst oxidation in an attempt to understand the catalytic cycle's early steps. Using [Ru(bpy)3]Cl2 and persulfate as the photosensitizer and the oxidative quencher, respectively, flash-photolysis was employed to gather evidence of the one-electron oxidized catalyst and to follow intermediates that could previously not be resolved temporally by electrochemical means.Printed electrodes (PEs) were fabricated using graphite as the conductive material and a polymer binder P(MMA-s-HEMA). The PEs were then covalently functionalized with [CuMac]2−using an in-situ electroreduction of the corresponding bis(diazonium) compound (N2)2[CuMac]. The resulting heterogenized catalyst's activity was evaluated by cyclic voltammetry to find that it was impeded compared to that of [CuMac]2− in homogeneous solution phase.Finally, a ruthenium-based coordination oligomer water oxidation catalyst was integrated into a flow-electrolyzer powered by a perovskite/perovskite tandem solar cell to drive water splitting by light. An operational voltage of 1.4 V was achieved, and a solar-to-hydrogen efficiency (STH) of 12.5 %. However, the stability of the system remains to be improved, which could be achieved by changing the membrane separating the two electrolyte compartments. Such adjustments can fine-tune the local pH surrounding the catalyst, which is an essential parameter for catalyst activity and integrity.
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| 38. |
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| 39. |
- Roeling, Erik M., et al.
(författare)
-
Organic electronic ratchets doing work
- 2011
-
Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 10:1, s. 51-55
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility to extract work from periodic, undirected forces has intrigued scientists for over a century-in particular, the rectification of undirected motion of particles by ratchet potentials, which are periodic but asymmetric functions. Introduced by Smoluchowski and Feynman(1,2) to study the (dis)ability to generate motion from an equilibrium situation, ratchets operate out of equilibrium, where the second law of thermodynamics no longer applies. Although ratchet systems have been both identified in nature(3,4) and used in the laboratory for the directed motion of microscopic objects(5-9), electronic ratchets(10-13) have been of limited use, as they typically operate at cryogenic temperatures and generate subnanoampere currents and submillivolt voltages(10-14). Here, we present organic electronic ratchets that operate up to radio frequencies at room temperature and generate currents and voltages that are orders of magnitude larger. This enables their use as a d.c. power source. We integrated the ratchets into logic circuits, in which they act as the d.c. equivalent of the a. c. transformer, and generate enough power to drive the circuitry. Our findings show that electronic ratchets may be of actual use.
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| 40. |
- Roeling, Erik M., et al.
(författare)
-
Scaling of characteristic frequencies of organic electronic ratchets
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:4
-
Tidskriftsartikel (refereegranskat)abstract
- The scaling of the characteristic frequencies of electronic ratchets operating in a flashing mode is investigated by measurements and numerical simulations. The ratchets are based on organic field effect transistors operated in accumulation mode. Oscillating potentials applied to asymmetrically spaced interdigitated finger electrodes embedded in the gate dielectric create a time-dependent, spatially asymmetric perturbation of the transistor channel potential. As a result, a net dc current can flow between source and drain despite zero source-drain bias. The frequency at current maximum is linearly dependent on the charge carrier density and the charge carrier mobility and inversely proportional to the squared length of the ratchet period, which can be related to the RC time of one asymmetric unit. Counterintuitively, it is independent of driving amplitude. Furthermore, the frequency at current maximum depends on the asymmetry of the ratchet potential, whereas the frequency of maximum charge pumping efficiency does not.
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| 41. |
- Roeling, Erik M., et al.
(författare)
-
The performance of organic electronic ratchets
- 2012
-
Ingår i: AIP Advances. - : American Institute of Physics (AIP): Open Access Journals / AIP Publishing LLC. - 2158-3226. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Organic electronic ratchets rectify time-correlated external driving forces, giving output powers that can drive electronic circuitry. In this work their performance characteristics are investigated using numerical modeling and measurements. It is shown how the characteristic parameters of the time-varying asymmetric potential like length scales and amplitude, as well as the density and mobility of the charge carriers in the device influence the performance characteristics. Various ratchet efficiencies and their relations are discussed. With all settings close to optimum, a ratchet with charge displacement and power efficiencies close to 50% and 7% respectively is obtained. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3677934]
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| 42. |
- Roelofs, W. S. Christian, et al.
(författare)
-
Contactless charge carrier mobility measurement in organic field-effect transistors
- 2014
-
Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 15:11, s. 2855-2861
-
Tidskriftsartikel (refereegranskat)abstract
- With the increasing performance of organic semiconductors, contact resistances become an almost fundamental problem, obstructing the accurate measurement of charge carrier mobilities. Here, a generally applicable method is presented to determine the true charge carrier mobility in an organic field-effect transistor (OFET). The method uses two additional finger-shaped gates that capacitively generate and probe an alternating current in the OFET channel. The time lag between drive and probe can directly be related to the mobility, as is shown experimentally and numerically. As the scheme does not require the injection or uptake of charges it is fundamentally insensitive to contact resistances. Particularly for ambipolar materials the true mobilities are found to be substantially larger than determined by conventional (direct current) schemes.
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| 43. |
- Roelofs, W.S. Christian, et al.
(författare)
-
Scanning tunnelling microscopy on organic field-effect transistors based on intrinsic pentacene
- 2014
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:26, s. 263301-
-
Tidskriftsartikel (refereegranskat)abstract
- The full potential of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy for in-situ characterization of organic semiconductors has so far not been accessible. Here, we demonstrate that the underlying problem, the low intrinsic conductivity, can be overcome by working in a field-effect geometry. We present high resolution surface topographies obtained by STM on pentacene organic field-effect transistors (OFETs). By virtue of the OFET geometry, the hole accumulation layer that is present at sufficiently negative gate bias acts as back contact, collecting the tunnelling current. The presence of a true tunnelling gap is established, as is the need for the presence of an accumulation layer. The tunnelling current vs. tip bias showed rectifying behaviour, which is rationalized in terms of the tip acting as a second gate on the unipolar semiconductor. An explanatory band diagram is presented. The measurements shown indicate that intrinsic organic semiconductors can be in-situ characterized with high spatial and energetic resolution in functional devices.
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| 44. |
- Schijven, Dick, et al.
(författare)
-
Large-scale analysis of structural brain asymmetries in schizophrenia via the ENIGMA consortium
- 2023
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 120:14
-
Tidskriftsartikel (refereegranskat)abstract
- Left-right asymmetry is an important organizing feature of the healthy brain that may be altered in schizophrenia, but most studies have used relatively small samples and heterogeneous approaches, resulting in equivocal findings. We carried out the largest case-control study of structural brain asymmetries in schizophrenia, with MRI data from 5,080 affected individuals and 6,015 controls across 46 datasets, using a single image analysis protocol. Asymmetry indexes were calculated for global and regional cortical thickness, surface area, and subcortical volume measures. Differences of asymmetry were calculated between affected individuals and controls per dataset, and effect sizes were meta-analyzed across datasets. Small average case-control differences were observed for thickness asymmetries of the rostral anterior cingulate and the middle temporal gyrus, both driven by thinner left-hemispheric cortices in schizophrenia. Analyses of these asymmetries with respect to the use of antipsychotic medication and other clinical variables did not show any significant associations. Assessment of age- and sex-specific effects revealed a stronger average leftward asymmetry of pallidum volume between older cases and controls. Case-control differences in a multivariate context were assessed in a subset of the data (N = 2,029), which revealed that 7% of the variance across all structural asymmetries was explained by case-control status. Subtle case-control differences of brain macrostructural asymmetry may reflect differences at the molecular, cytoarchitectonic, or circuit levels that have functional relevance for the disorder. Reduced left middle temporal cortical thickness is consistent with altered left-hemisphere language network organization in schizophrenia.
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| 45. |
- Stuhr-Hansen, Nicolai, et al.
(författare)
-
Organoselenium-Substituted Poly(p-phenylenevinylene)
- 2005
-
Ingår i: Heteroatom Chemistry. - : Wiley. - 1042-7163 .- 1098-1071. ; 16:7, s. 656-662
-
Tidskriftsartikel (refereegranskat)abstract
- A new type of conjugated polymer, organoselenium substituted poly(p-pheylenevinylene) (PPV), was synthesized from the corresponding alkylselenenyl p-xylylene dibromide via a Gilch route using potassium tert-butoxide in THF. The p-xylylene dibromide precursors were synthesized by reacting lithiated bis(methoxymethyl)benzenes with elemental selenium, followed by alkylation of the generated selenolates. As a final demasking step, the bromomethyl functions were liberated by ether cleavage using boron tribromide. Bis-alkylselenenyl PPV was obtained with an average molecular weight Mw of approximately 300,000 g/mol and with polydispersity Mw/Mn=2. Due to low solubility, monoalkylselenenyl PPV was obtained with a considerably lower average molecular weight in the proximity of 16,000 g/mol and with a polydispersity slightly larger than 3. Absorption and flourescence spectroscopy revealed that the bis-alkylselenenyl PPV is extensively conjugated.
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| 46. |
- Tang, Zheng
(författare)
-
Chargeand Light Management in Organic Solar Cells
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solar cells based on organic materials are extensively investigated both in academia and industry, owing to their potential of being inexpensive, lightweight, flexible and suitable for roll-to-roll production. Performance of organic solar cells has been rapidly improving, and the state of the art organic solar cells have an efficiency over 10%.This thesis aims to provide a comprehensive study of device engineering and device physics of organic solar cells. The ambition has been to investigate and optimize the conditions for light in-coupling and charge extraction in organic solar cells with alternative geometries. The ultimate goal is to propose methods that could potentially get the power conversion efficiency of organic solar cells with industrially compatible geometries over the current limit of 10%.To achieve such a goal, we employed a conjugated polymer as an interface modifier to improve the surface and electrical properties of substrate electrodes for solar cells with active layers based on blends containing conjugated polymers and fullerenes. A possibility of improving photovoltaic performance of easily fabricated reverse geometry solar cells (bottom metal cathode/active layer/top transparent anode) has been demonstrated via this simple interface modification. Systematic investigations revealed that the enhanced device performance was not only related to the modified active layer/electrode interface but also changes in the bulk of the active layer. Consequently, the device performance of a reversed solar cell was found to be as good as that of a standard solar cell. The understanding of the effects of the interlayer modification on the performance of reversed solar cells, and the methodology provided in this thesis is a guideline for further studying and developing interface materials for highly efficient organic solar cells.An ITO electrode was further converted into a cathode by the polymer interlayer to construct semi-transparent solar cells with great potentials for building integrated photovoltaic applications. By stacking semi-transparent solar cells on top of each other, we showed that light can be more efficiently harvested compared to a conventional architecture solar cell. It has also been demonstrated that semitransparent solar cells combined with macroscopic light trapping elements can also be highly efficient.However, this thesis is not only about papers that I have published as a graduate student. The first five chapters have been included to provide background in the field of organic photovoltaics.
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| 47. |
- van Breemen, Albert, et al.
(författare)
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Surface Directed Phase Separation of Semiconductor Ferroelectric Polymer Blends and their Use in Non-Volatile Memories
- 2015
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlagsgesellschaft. - 1616-301X .- 1616-3028. ; 25:2, s. 278-286
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Tidskriftsartikel (refereegranskat)abstract
- The polymer phase separation of P(VDF-TrFE):F8BT blends is studied in detail. Its morphology is key to the operation and performance of memory diodes. In this study, it is demonstrated that it is possible to direct the semiconducting domains of a phase-separating mixture of P(VDF-TrFE) and F8BT in a thin film into a highly ordered 2D lattice by means of surface directed phase separation. Numerical simulation of the surface-controlled de-mixing process provides insight in the ability of the substrate pattern to direct the phase separation, and hence the regularity of the domain pattern in the final dry blend layer. By optimizing the ratio of the blend components, the number of electrically active semiconductor domains is maximized. Pattern replication on a cm-scale is achieved, and improved functional device performance is demonstrated in the form of a 10-fold increase of the ON-current and a sixfold increase in current modulation. This approach therefore provides a simple and scalable means to higher density integration, the ultimate target being a single semiconducting domain per memory cell.
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| 48. |
- van de Ruit, Kevin, et al.
(författare)
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Quasi-One Dimensional in-Plane Conductivity in Filamentary Films of PEDOT:PSS
- 2013
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 23:46, s. 5778-5786
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism and magnitude of the in-plane conductivity of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) thin fi lms is determined using temperature dependent conductivity measurements for various PEDOT: PSS weight ratios with and without a high boiling solvent (HBS). Without the HBS the in-plane conductivity of PEDOT: PSS is lower and for all studied weight ratios well described by the relation s = s0exp[-T0 T 0.5] with T 0 a characteristic temperature. The exponent 0.5 indicates quasi-one dimensional (quasi-1D) variable range hopping (VRH). The conductivity prefactor s 0 varies over three orders of magnitudes and follows a power law s 0. c 3.5 PEDOT with c PEDOT the weight fraction of PEDOT in PEDOT: PSS. The fi eld dependent conductivity is consistent with quasi-1D VRH. Combined, these observations suggest that conductance takes place via a percolating network of quasi-1D fi laments. Using transmission electron microscopy (TEM) fi lamentary structures are observed in vitrifi ed dispersions and dried fi lms. For PEDOT: PSS fi lms with HBS, the conductivity also exhibits quasi-1D VRH behavior when the temperature is less than 200 K. The low characteristic temperature T 0 indicates that HBStreated fi lms are close to the critical regime between a metal and an insulator. In this case, the conductivity prefactor scales linearly with c PEDOT, indicating the conduction is no longer limited by a percolation of fi laments. The lack of observable changes in TEM upon processing with the HBS suggests that the changes in conductivity are due to a smaller spread in the conductivities of individual fi laments, or a higher probability for neighboring fi laments to be connected rather than being caused by major morphological modifi cation of the material.
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| 49. |
- van de Ruit, Kevin, et al.
(författare)
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The Curious Out-of-Plane Conductivity of PEDOT:PSS
- 2013
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 23:46, s. 5787-5793
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Tidskriftsartikel (refereegranskat)abstract
- For its application as transparent conductor in light-emitting diodes and photovoltaic cells, both the in-plane and out-of-plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out-of-plane conductivity and those that do, report widely varying results. Here a systematic study of the out-of-plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out-of-plane conductivity with only a 3-4-fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model.
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| 50. |
- van der Hofstad, Tom G. J., et al.
(författare)
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Carrier Recombination in Polymer Fullerene Solar Cells Probed by Reversible Exchange of Charge between the Active Layer and Electrodes Induced by a Linearly Varying Voltage
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 117:7, s. 3210-3220
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Tidskriftsartikel (refereegranskat)abstract
- The use of a voltage pulse that varies linearly with time and that is symmetric in time around t = 0 allows for simultaneous determination of (photo)capacitance and (photo)conductance of polymer solar cells. From the measured capacitance, an average density of reversibly extractable carriers is determined, and the result is compared to numerical drift-diffusion simulations. Results are in agreement with large charge densities near the contacts that can be exchanged with the electrode in a thermodynamically reversible manner upon changing the voltage. The combined determination of capacitance and conductance yields a relaxation time tau(rel) for photogenerated charge carriers. Results on thermally annealed poly(3-hexylthiopene):fullerene bulk heterojunction solar cells indicate tau(rel) similar to 2 mu s, limited by extraction and not significantly affected by bimolecular recombination under intensities up to 1 sun. In contrast, for small bandgap poly(diketopyrrolopyrrole-alt-quinquethiophene)-fullerene solar cells with similar to 5% power conversion efficiency, tau(rel) is limited by bimolecular recombination. This illustrates the need for very fast charge transport rates to avoid losses due to bimolecular recombination in solar cells with high charge generation rates. Conclusions from the charge exchange experiments are confirmed by time domain measurements using pulsed illumination.
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