| 1. |
- Anacleto, Pedro, et al.
(författare)
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Precisely nanostructured HfO2 rear passivation layers for ultra-thin Cu(In,Ga)Se-2
- 2022
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Ingår i: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 30:11, s. 1289-1297
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Tidskriftsartikel (refereegranskat)abstract
- The quest for material-efficient Cu(In,Ga)Se-2 (CIGS) solar cells encourages the development of ultra-thin absorbers. Their use reduces material consumption and energy usage during production by increasing the throughput. Thereby, both the bill of materials as well as the energy and capital costs are reduced. However, because thin absorbers are prone to increase back contact recombination, back surface passivation schemes are necessary to reach a similar or higher conversion efficiency than for absorbers with conventional thickness. Here, we investigate nanostructured hafnium oxide (HfO2) rear passivation layers for ultra-thin CIGS solar cells. We fabricate regular arrays of point contacts with 200 nm diameter through HfO2 layers with thicknesses between 7 and 40 nm using electron beam lithography and reactive ion etching. The current-voltage curves of solar cells with a 500 nm thick CIGS absorber layer and the nanostructured passivation layer show improved performance concerning V-oc and J(sc) compared to non-passivated reference devices. Furthermore, external quantum efficiency and optical reflection confirm an effective passivation behavior, with an average efficiency increase of up to 1.2% for the cells with the 40 nm thick HfO2 layer. In addition, simulation work shows that even 40 nm thick HfO2 passivation layers have only a minimal effect on the optical properties of ultra-thin CIGS solar cells, and hence, the photocurrent increase verified experimentally stems from electrical improvements caused by the HfO2 layer passivation effect. We also investigate the impact of ultra-thin (0.3, 0.6, 1.3, and 2.5 nm) non-patterned HfO2 passivation layers on the same type of solar cells. However, these results showed no improvement in solar cell performance, despite an increase in the current density with layer thickness.
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| 2. |
- Apell, Peter, 1952, et al.
(författare)
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High optical absorption in graphene
- 2012
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Ingår i: arXiv.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A simple analysis is performed for the absorption properties of graphene sandwiched between two media. For a proper choice of media and graphene doping/gating one can approach 50-100% absorption in the GHz-THz range for the one atom thick material. This absorption is controlled by a characteristic chemical potential which depends only on carrier life-time and the indexes of refraction of the dielectric embedding.
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| 6. |
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| 7. |
- Bilousov, Oleksandr V., et al.
(författare)
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ALD of phase controlled tin monosulfide thin films
- 2017
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Konferensbidrag (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the role of absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductor candidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1].Here, we present an important step to further control and understand SnS film properties produced using low temperature ALD with Sn(acac)2 and H2S as precursors. We show that the SnS film properties vary over a rather wide range depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic (π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry [2].1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463.2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel-Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry of Materials 29 (7) (2017) 2969–2978.
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| 8. |
- Bilousov, Oleksandr V., et al.
(författare)
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Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide
- 2017
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 29:7, s. 2969-2978
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Tidskriftsartikel (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising light-absorbing material with weak environmental constraints for application in thin film solar cells. In this paper, we present low-temperature atomic layer deposition (ALD) of high-purity SnS of both cubic and orthorhombic phases. Using tin(II) 2,4-pentanedionate [Sn(acac)(2)] and hydrogen sulfide (H2S) as precursors, controlled growth of the two polymorphs is achieved. Quartz crystal microbalance measurements are used to establish saturated conditions and show that the SnS ALD is self-limiting over temperatures from at least 80 to 160 degrees C. In this temperature window, a stable mass gain of 19 ng cm(-2) cycle(-1) is observed. The SnS thin film crystal structure and morphology undergo significant changes depending on the conditions. High-resolution transmission electron microscopy and X-ray diffraction demonstrate that fully saturated growth requires a large H2S dose and results in the cubic phase. Smaller H2S doses and higher temperatures favor the orthorhombic phase. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry. The orthorhombic phase displays a wide (0.3-0.4 eV) Urbach tail in the near-infrared region, ascribed to its nanoscale structural disorder and/or to sulfur vacancy-induced gap states. In contrast, the cubic phase is smooth and void-free and shows a well-defined, direct forbidden-type bandgap of 1.64 eV.
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| 9. |
- Bilousov, Oleksandr V., et al.
(författare)
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Substrate Effects on Crystal Phase in Atomic Layer Deposition of Tin Monosulfide
- 2021
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 33:8, s. 2901-2912
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Tidskriftsartikel (refereegranskat)abstract
- Obtaining single-phase tin monosulfide (SnS) films at low temperatures is challenging since cubic (π-SnS) and orthorhombic (α-SnS) polymorphs have similar energies of formation and grow under similar conditions. Here, we show that in atomic layer deposition (ALD) of polycrystalline SnS using tin(II) acetylacetonate and H2S precursors, the substrate surface greatly influences the SnS phase evolution. For example, a silicon (100) substrate, with a highly hydroxylated surface, favors the growth of α-SnS. Meanwhile, ozone treatment or preannealing of the same substrate leads to mainly π-SnS. Just a few ALD cycles of another oxide or sulfide can even more substantially alter the outcome. Substrates that favor α-SnS growth typically produce initially enhanced growth rates, while those promoting π-SnS are partially surface-poisoned by the acetylacetonate precursor ligands. Growth of either polymorph is self-sustained after its initiation, and the sustaining factor appears to be the surface–ligand interaction; π-SnS preferentially evolves on substrates and π-SnS surfaces that are rich in highly reactive dangling bonds, while chemically inert substrates and α-SnS surfaces promote α-SnS. While lattice matching is less central, the role of ligand bonding in SnS ALD also helps explain the previously reported phase dependence on growth temperature and H2S precursor dose and shows promise for area-selective ALD of SnS.
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| 10. |
- Brännström, Margareta, et al.
(författare)
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Unequal care for dying patients in Sweden : a comparative registry study of deaths from heart disease and cancer
- 2012
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Ingår i: European Journal of Cardiovascular Nursing. - : Elsevier. - 1474-5151 .- 1873-1953. ; 11:4, s. 454-459
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The Swedish Palliative Registry is a nationwide quality registry aimed at facilitating improvement in end-of-life care. The goal is for the registry to list and report quality indicators related to care during the last week of life in all cases expected death in Sweden.AIM: To examine the quality of care during the last week of life as reported to the registry for patients with heart disease compared to those with cancer.METHOD: A retrospective registry study.RESULTS: Patients dying of heart disease compared to those dying from cancer had more shortness of breath, fewer drugs prescribed as needed against the usual symptoms and often died alone. Furthermore, they and their close relatives received less information about the imminence of death and bereavement follow-up was less common. The healthcare personnel were less aware of the heart disease patients' symptoms and less often knew about where they wished to die.CONCLUSION: Great differences were found in registered end-of-life care suggesting that the care given to patients with heart disease and cancer was unequal even after adjustment for age, sex and setting at the time of death. If our observational findings are confirmed in future studies there is obviously a need for new models for end-of-life management in order to facilitate the provision of equal care to dying patients regardless of diagnosis.
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| 11. |
- Cheng, Haoliang, et al.
(författare)
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Atomic Layer Deposition of SnO2 as an Electron Transport Material for Solid-State P-type Dye-Sensitized Solar Cells
- 2022
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:10, s. 12022-12028
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Tidskriftsartikel (refereegranskat)abstract
- Tin oxide (SnO2) as an electron transport material was prepared by atomic layer deposition in dye-sensitized NiO films to fabricate solid-state p-type dye-sensitized solar cells using two organic dyes PB6 and TIP as photosensitizers. Due to the excellent electron mobility and satisfactory penetration of SnO2 material into the NiO film, a record photocurrent density over 1 mA cm–2 was achieved with a power conversion efficiency of 0.14%. The effect of an inserted Al2O3 layer between the dye-sensitized NiO and SnO2 layer on photovoltaic performance of the devices was also investigated. The results suggest that the charge recombination between NiO and SnO2 can be significantly suppressed, showing prolonged charge lifetime and enhanced photovoltage.
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| 12. |
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| 14. |
- Ebadi, Seyed Morteza
(författare)
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Design and Numerical Modelling of Nanoplasmonic Structures at Near-Infrared for Telecom Applications
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industrial innovation is mostly driven by miniaturization. As a result of remarkable technological advancements in the fields of equipment, materials and production processes, transistor, the fundamental active component in conventional electronics, has shrunk in size. Semiconductor technology is unique in that all performance metrics are enhanced, while at the same time unit prices are reduced. Moore’s Law, which predicts that the number of components per chip will double every two years, was established in 1965, and the industry has been able to keep up with this prophetic prognosis since. Thermal management, on the other hand, has become a key limiting factor for current electronic circuits and is set to put a stop to Moore’s Law. Given the fact that complementary metal oxide semiconductor (CMOS) scaling is reaching fundamental limits, there are several new alternative processing devices and architectures that have been investigated for both traditional integrated circuit (IC) technologies and novel technologies, including new technologies aimed at contributing to advances in scaling progress and cost reductions in manufacturing operations in the coming decades. These factors will encourage the development of new information processing and memory systems, new technologies for integrating numerous features heterogeneously and new system architectural design layouts, among other things. Energy efficiency is advantageous from a sustainability perspective and for consumer electronics, for which fewer power-hungry components mean longer times between charges and smaller batteries. The creation of novel chip-scale tools that can aid in the transfer of information across optical frequencies and microscale photonics between nanoscale electronic devices is now a possibility. Bridging this technological gap may be achieved by plasmonics. The incorporation of plasmonic, photonic and electrical components on a single chip may lead to a number of innovative breakthroughs. Photonic integrated circuits (PICs) enable the realization of ultra-small, high-efficiency, ultra-responsive and CMOS-compatible devices that can be used in applications ranging from optical wireless communication systems (6G and beyond) and supercomputers to health and energy. This thesis provides a platform from which to design nanoplasmonic devices while facilitating high-transmission and/or absorption efficiency, miniaturized size and the use of near-infrared (NIR) wavelengths for telecom applications. With a significant amount of Internet traffic transmitted optically, communication systems are further tightening the requirements for the development of new optical devices. Several new device structures based on the metal-insulator-metal (MIM) plasmonic waveguide are proposed and investigated using performance metrics. The transmission line theory (TLM) from microwave circuit theory and coupled mode theory (CMT) is studied and employed in the design process of the nanostructures, in particular to address the losses in plasmonic-based devices, which has been the major factor hampering their widespread usage in communication systems. By taking advantage of well-established microwave circuit theory (through new design that paves the way for mitigating these losses and enabling efficient transmission of power flow in the optical devices), we have suggested a number of high-transmission efficiency nanodevices that offer highly competitive performance compared with other platforms. As a result, a promising future for plasmonic technology, which would enable design and fabrication of multipurpose and multifunctional optical devices that are efficient in terms of losses, footprint and capability of integrating active devices, is anticipated.
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| 15. |
- Edoff, Marika, 1965-, et al.
(författare)
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Back Contact Passivation Effects in Bi-Facial Thin CIGS Solar Cells
- 2016
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Ingår i: 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC). - : IEEE. - 9781509027248 ; , s. 3527-3529
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Konferensbidrag (refereegranskat)abstract
- Bi-facial solar cells with ultrathin CIGS solar cells are fabricated to investigate the influence of back contact passivation. Solar cells with CIGS thicknesses of 300 and 500 nm and with an ultrathin transparent Mo layer are characterized using EQE measurements from both the front and the rear side as well as with I-V measurements. Back contact passivation consisting of Al2O3 deposited by atomic layer deposition and nano-sized point contact openings is used. The results are compared to cells with only the transparent Mo layer as back contact. We find a significant effect of the passivation manifested as an increase in the current density of the solar cells with the passivation.
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| 16. |
- Eneroth, Carl, et al.
(författare)
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Lost the connection?
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 17. |
- Ericson, Tove, 1983-, et al.
(författare)
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Zinc-Tin-Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd-Free Cu2ZnSnS4 Solar Cell
- 2017
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 1:5
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Tidskriftsartikel (refereegranskat)abstract
- Zn1−xSnxOy (ZTO) has yielded promising results as a buffer material for the full sulfur Cu2ZnSnS4 (CZTS), with efficiencies continuously surpassing its CdS-references. ZTO can be deposited by atomic layer deposition (ALD), enabling tuning of the conduction band position through the choice of metal ratio or deposition temperature. Thus, an optimization of the conduction band alignment between ZTO and CZTS can be achieved. The ZTO bandgap is generally larger than that of CdS and can therefore yield higher currents due to reduced losses in the short wavelength region. Another advantage is the possibility to omit the toxic Cd. In this study, the ALD process temperature was varied from 105 to 165 °C. Current-blocked devices were obtained at 105 °C, while the highest open-circuit voltage and device efficiency was achieved for 145 °C. The highest fill factor was seen at 165 °C. The best efficiency reached in this study was 9.0%, which, to our knowledge, is the highest efficiency reported for Cd-free full-sulfur CZTS. We also show that the effect of heat needs to be taken into account. The results indicate that part of the device improvement comes from heating the absorber, but that the benefit of using a ZTO-buffer is clear.
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| 18. |
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| 19. |
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| 20. |
- Grannäs, Jan, 1967-
(författare)
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Framtidens demokratiska medborgare : Om ungdomar, medborgarskap och demokratifostran i svensk skola
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis attempts to deepen our understanding of the democratic assignment for Swedish schools. The school is a public space that all children and youth are a part of which gives it a prominent opportunity for fostering democratic citizens of the future. The purpose of the study is to increase the knowledge of this assignment, based on the students’ stories of how they experience it. The theoretical framework draws upon a spatial perspective and educational theory inspired by a radical view of democracy. A multiple case study was conducted based on three cases, chosen in order to achieve socioeconomic variation. A mixed method approach has been applied to the study: interviews, observations, documents and quantitative data have been analyzed using a thematic analysis framework. The results show that the democratic assignment of schools is complex and filled with legal, social, ideological, and ethical tensions. For the purpose of creating a school environment that meets the democratic assignment, systematic work and guidelines for school personnel, students, and parents appear to be necessary. The study has clearly shown that the conditions for the democratic assignment may differ markedly between schools and that peer socialization is of great importance for the outcome. The influence and potential of diversity on the democratic assignment of schools is clear. From a curriculum micro perspective, the study has brought attention to how the view of the (non-)competent student is relevant for the democratic assignment, as well as the bases on which this notion of (non-)competence rest. It is suggested that the view of the democratic assignment is extended, from a narrow focus on democratic decision-making processes to a wider focus that also takes into account the ongoing everyday negotiation processes between teachers and students that have impact on what is perceived as political action and democratic arenas.
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| 26. |
- Gusak, Viktoria, 1983, et al.
(författare)
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Thickness Dependence of Plasmonic Charge Carrier Generation in Ultrathin a-Si:H Layers for Solar Cells
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 5:8, s. 6218-6225
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Tidskriftsartikel (refereegranskat)abstract
- Nanocomposite layers of Ag nanoparticles and a-Si:H film constitute attractive candidates for the realization of ultrathin "two- dimensional" plasmonic solar cells, with an ideal 18% efficiency predicted for an average layer thickness of only 20 nm. By combining optical spectroscopy with photoconductivity measurements, we here characterize different contributions to the light absorption and charge carrier generation in such nanocomposites. We focus in particular on the important role of the absorber layer thickness for these processes, by studying a range of a-Si:H thicknesses from 9 to 67 nm. Through detailed comparison with numerical calculations by the finite element method, observed experimental features are connected to specific resonance modes and charge carrier generation mechanisms. The influence of dipolar and quadrupolar near-field distributions are evaluated with respect to different figures of merit for plasmonic solar cells. We briefly discuss how the present findings may be implemented in practical solar cell configurations. © 2011 American Chemical Society.
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| 27. |
- Hinnemo, Malkolm, 1986-, et al.
(författare)
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On Monolayer Formation of Pyrenebutyric Acid on Graphene
- 2017
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 33:15, s. 3588-3593
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Tidskriftsartikel (refereegranskat)abstract
- As a two-dimensional material with high charge carrier mobility, graphene may offer ultrahigh sensitivity in biosensing. To realize this, the first step is to functionalize the graphene. This is commonly done by using 1-pyrenebutyric acid (PBA) as a linker for biornolecules. However, the adsorption of PBA on graphene remains poorly understood despite reports of successful biosensors functionalized via this route. Here, the PBA adsorption on graphene is characterized through a combination of Raman spectroscopy, ab initio calculations, and spectroscopic ellipsometry. The PBA molecules are found to form a self-assembled monolayer on graphene, the formation of which is self-limiting and Langmuirian. Intriguingly, in concentrated solutions, the PBA molecules are found to stand up and stack horizontally with their edges contacting the graphene surface. This morphology could facilitate a surface densely populated with carboxylic functional groups. Spectroscopic analyses show that the monolayer saturates at 5.3 PBA molecules per nm(2) and measures similar to 0.7 nm in thickness. The morphology study of this PBA monolayer sheds light on the pi-pi stacking of small-molecule systems on graphene and provides an excellent base for optimizing functionalization procedures.
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| 28. |
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| 29. |
- Hinnemo, Malkolm, et al.
(författare)
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Scalable residue-free graphene for surface-enhanced Raman scattering
- 2016
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 98, s. 567-571
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Tidskriftsartikel (refereegranskat)abstract
- A room-temperature polymer-assisted transfer process is developed for large-area, single-layer graphene grown by means of chemical vapor deposition (CVD). This process leads to transferred graphene layers free of polymer contamination. The absence of polymer residues boosts the surface-enhanced Raman scattering (SERS) of the CVD graphene with gold nanoparticles (Au NPs) deposited atop by evaporation. The SERS enhancement of the CVD graphene reaches similar to 120 for the characteristic 2D peak of graphene, the highest enhancement factor achieved to date, when the Au NPs are at the threshold of percolation. Our simulation supported by experiment suggests that the polymer residues persistently present on the graphene transferred by the conventional polymer-assisted method are equivalent to an ultrathin film of less than 1 nm thickness. The presence of polymer residues drastically reduces SERS due to the separation of the Au NPs from the underlying graphene. The scalability of CVD graphene opens up for the possibility of graphene-based SERS sensors.
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| 30. |
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| 33. |
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| 34. |
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| 36. |
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| 37. |
- Hägglund, Carl, 1975-, et al.
(författare)
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Growth, intermixing, and surface phase formation for zinc tin oxide nanolaminates produced by atomic layer deposition
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 34:2
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Tidskriftsartikel (refereegranskat)abstract
- A broad and expanding range of materials can be produced by atomic layer deposition at relatively low temperatures, including both oxides and metals. For many applications of interest, however, it is desirable to grow more tailored and complex materials such as semiconductors with a certain doping, mixed oxides, and metallic alloys. How well such mixed materials can be accomplished with ALD requires knowledge of the conditions under which the resulting films will be mixed, solid solutions, or laminated. The growth and lamination of zinc oxide and tin oxide is studied here by means of the extremely surface sensitive technique of low energy ion scattering, combined with bulk composition and thickness determination, and X-ray diffraction. At the low temperatures used for deposition (150 °C) there is little evidence for atomic scale mixing even with the smallest possible bilayer period, and instead a morphology with small ZnO inclusions in a SnOx matrix is deduced. Post-annealing of such laminates above 400 °C however produces a stable surface phase with a 30% increased density. From the surface stoichiometry, this is likely the inverted spinel of zinc stannate, Zn2SnO4. Annealing to 800 °C results in films containing crystalline Zn2SnO4, or multilayered films of crystalline ZnO, Zn2SnO4 and SnO2 phases, depending on the bilayer period.
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| 38. |
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| 39. |
- Hägglund, Carl, 1975
(författare)
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Ljus blir el
- 2006
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Ingår i: Miljöportalen.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 40. |
- Hägglund, Carl, 1975, et al.
(författare)
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Maximized Optical Absorption in Ultrathin Films and Its Application to Plasmon-Based Two-Dimensional Photovoltaics
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:8, s. 3135-3141
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Tidskriftsartikel (refereegranskat)abstract
- For ultrathin films of a given material, light absorption is proportional to the film thickness. However, if the optical constants of the film are chosen in an optimal way, light absorption can be high even for extremely thin films and optical path length. We derive the optimal conditions and show how the maximized absorptance depends on film thickness. It is then shown that the optimal situation can be emulated by tuning of the geometric parameters in feasible nanocomposites combining plasmonic materials with semiconductors. Useful design criteria and estimates for the spatial absorption-distribution over the composite materials are provided. On the basis of efficient exchange of oscillator strength between the plasmonic and semiconductor constituents, a high quantum yield for semiconductor absorption can be achieved. The results are far-reaching with particularly promising opportunities for plasmonic solar cells.
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| 41. |
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| 42. |
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| 43. |
- Hägglund, Carl, 1975-
(författare)
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Multiscale Optical Modeling of Perovskite-Si Tandem Solar Cells
- 2022
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Ingår i: Frontiers in Photonics. - : Frontiers Media S.A.. - 2673-6853. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- With the success of silicon (Si) solar cell technology, research and development on higher efficiency multijunction solar cells is gaining much attention. Tandem cells with a perovskite top cell and a Si bottom cell show particular potential. However, the optical modeling of such devices is complicated by the broad range of length scales involved; the optically thin layers and nanoscale features of a perovskite solar cell require some version of wave optics or even full field electromagnetic (EM) calculations, while the micrometer scale structuring and large dimensions of Si cells are much more manageable using geometrical (ray) optics. In the present work, a method for combining EM and ray optical calculations is developed and described in detail, with examples provided in the software Comsol Multiphysics. For regions with thin films or nanoscale features, EM wave calculations are performed using the finite element method. These calculations provide the phase and amplitude of the waves diffracted into different orders, of which only the regular reflection and transmission are typically of relevance for nanoscale periodicity. In the ray optics simulation, the corresponding regions are implemented as diffracting interfaces, with deterministic transformations of the Stokes vector components according to the EM wave calculations. Meanwhile, the absorbed intensity of intersecting rays is recorded. The method is applied to separate perovskite and Si solar cells and to a few tandem solar cells of relevance for two- versus four-terminal configurations. Corrections for strongly absorbing media in the ray tracing algorithm, which use generalized versions of the Fresnel coefficients, Snell’s law and the Beer-Lambert law, are also evaluated. In a typical Si solar cell with a front surface structure of inverted pyramids, such corrections are found to reduce the absorption by up to 0.5 percentage units compared to a conventional ray tracing calculation. The difference is concluded to originate mainly from reduced absorption rates of inhomogeneous waves, rather than from enhanced escape probabilities for (quasi-) trapped rays at the Si front surface. The method is further applied to evaluate the effects of a plasmonic nanoparticle array, embedded in a perovskite solar cell stack that is located directly on the microstructured Si surface.
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| 44. |
- Hägglund, Carl, 1975
(författare)
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Nanoparticle plasmon influence on the charge carrier generation in solar cells
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is a potential threat to life on earth and to human society. It is by much evidence linked to the extensive use of fossil fuels in our present energy system. Replacing the fossil fuels by alternative sources of energy poses a tremendous challenge for mankind, but is not at all undoable. Of the many alternatives that can be employed, electricity producing photovoltaic solar cells are one of the most attractive long term solutions due to their scalability, flexibility, simplicity, environmental friendliness and a huge, reliable, physical potential for providing energy. However, they are not yet cost competitive for on-grid applications.An important route to reduce the cost of photovoltaic solar cells, is to accomplish the same or even improved efficiency as in today’s solar cells, with less (thinner) photoactive material. An interesting possibility in this respect is to employ localized surface plasmon resonances (LSPRs) for the initial light capture. A plasmon resonance is a collective oscillation of the conduction electrons which can be excited by electromagnetic radiation in small metal particles. Especially noble metal particles of nanoscale dimensions create LSPRs with very large optical cross sections in the visible and near infrared spectrum, which is the range of interest for photovoltaic applications. There are three possible mechanisms for plasmon enhanced conversion of incident light to free charge carriers in an adjacent photovoltaic junction: i) via a favorably modified electromagnetic (EM) far-field distribution, ii) via EM near-field enhancement close to the particles and iii) via charge carrier photoemission from the particles to the semiconductor substrate.In this thesis, the influence of noble metal nanoparticles on the charge carrier generation in two different types of photovoltaic solar cells, representing two extreme cases, were investigated experimentally and theoretically. The first is a planar version of the dye sensitized, Grätzel solar cell (DSSC), which relies on surface absorption of light in dye molecules. The second is a more conventional silicon (Si) pn-junction solar cell, where absorption takes place in the bulk of the material. Experiments and theory (including finite element calculations) primarily address the EM mechanisms i) and ii) outlined above, and indicate that near-field enhanced performance at the LSP resonance is possible for the surface absorption (DSSC) case, but that negative effects dominate for the bulk absorption (Si) case. On the other hand, enhanced coupling into the bulk substrate modes results in higher photocurrents for longer wavelengths. A possibility related to this is to couple energy into waveguided modes of thin photovoltaic layers via the plasmonic particles. In a parallell study dealing with laser induced restructuring of thin gold films, we found a very concrete example of such coupling; gold particles were moved and reshaped into a grating pattern, due to the formation of a standing wave involving guided modes of the thin Si3N4 substrate.
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| 45. |
- Hägglund, Carl, 1975, et al.
(författare)
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Nanoparticle plasmonics for 2D-photovoltaics: Mechanisms, Optimization, and Limits
- 2009
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 17:14, s. 11944-11957
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic nanostructures placed within or near photovoltaic (PV) layers are of high current interest for improving thin film solar cells. We demonstrate, by electrodynamics calculations, the feasibility of a new class of essentially two dimensional (2D) solar cells based on the very large optical cross sections of plasmonic nanoparticles. Conditions for inducing absorption in extremely thin PV layers via plasmon near-fields, are optimized in 2D-arrays of (i) core-shell particles, and (ii) plasmonic particles on planar layers. At the plasmon resonance, a pronounced optimum is found for the extinction coefficient of the PV material. We also characterize the influence of the dielectric environment, PV layer thickness and nanoparticle shape, size and spatial distribution. The response of the system is close to that of a 2D effective medium layer, and subject to a 50% absorption limit when the dielectric environment around the 2D layer is symmetric. In this case, a plasmon induced absorption of about 40% is demonstrated in PV layers as thin as 10 nm, using silver nanoparticle arrays of only 1 nm effective thickness. In an asymmetric environment, the useful absorption may be increased significantly for the same layer thicknesses. These new types of essentially 2D solar cells are concluded to have a large potential for reducing solar electricity costs.
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| 46. |
- Hägglund, Carl, 1975, et al.
(författare)
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Plasmonic Near-Field Absorbers for Ultrathin Solar Cells
- 2012
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:10, s. 1275-1285
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Forskningsöversikt (refereegranskat)abstract
- If the active layer of efficient solar cells could be made 100 times thinner than in today's thin film devices, their economic competitiveness would greatly benefit. However, conventional solar cell materials do not have the optical capability to allow for such thickness reductions without a substantial loss of light absorption. To address this challenge, the use of plasmon resonances in metal nanostructures to trap light and create charge carriers in a nearby semiconductor material is an interesting opportunity. In this Perspective, recent progress with regards to ultrathin (similar to 10 nm) plasmonic nanocomposites is reviewed. Their optimal internal geometry for plasmon near-field induced absorption is discussed, and a zero thickness effective medium representation is used to optimize stacks including an Al back reflector for photovoltaics. This shows that high conversion efficiencies (>20%) are possible even when taking surface scattering effects and thin passivating layers inserted between the metal and semiconductor into account.
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| 47. |
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| 48. |
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| 49. |
- Hägglund, Carl, 1975-, et al.
(författare)
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Strong coupling of plasmon and nanocavity modes for dual-band, near-perfect absorbers and ultrathin photovoltaics
- 2016
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 3:3, s. 456-463
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Tidskriftsartikel (refereegranskat)abstract
- When optical resonances interact strongly, hybridized modes are formed with mixed properties inherited from the basic modes. Strong coupling therefore tends to equalize properties such as damping and oscillator strength of the spectrally separate resonance modes. This effect is here shown to be very useful for the realization of near perfect dual-band absorption with ultrathin (~10 nm) layers in a simple geometry. Absorber layers are constructed by atomic layer deposition of the heavy-damping semiconductor tin monosulfide (SnS) onto a two-dimensional gold nanodot array. In combination with a thin (55 nm) SiO2 spacer layer and a highly reflective Al film on the back, a semi-open nanocavity is formed. The SnS coated array supports a localized surface plasmon resonance in the vicinity of the lowest order anti-symmetric Fabry-Perot resonance of the nanocavity. Very strong coupling of the two resonances is evident through anti-crossing behavior with a minimum peak splitting of 400 meV, amounting to 24% of the plasmon resonance energy. The mode equalization resulting from this strong interaction enables simultaneous optical impedance matching of the system at both resonances, and thereby two near perfect absorption peaks which together cover a broad spectral range. When paired with the heavy damping from SnS band-to-band transitions, this further enables approximately 60% of normal incident solar photons with energies exceeding the bandgap to be absorbed in the 10 nm SnS coating. Thereby, these results establish a distinct relevance of strong coupling phenomena to efficient, nanoscale photovoltaic absorbers and more generally for fulfilling a specific optical condition at multiple spectral positions.
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| 50. |
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