| 1. |
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| 2. |
- Aartsen, M. G., et al.
(författare)
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Development of a general analysis and unfolding scheme and its application to measure the energy spectrum of atmospheric neutrinos with IceCube
- 2015
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 75:3
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Tidskriftsartikel (refereegranskat)abstract
- We present the development and application of a generic analysis scheme for the measurement of neutrino spectra with the IceCube detector. This scheme is based on regularized unfolding, preceded by an event selection which uses a Minimum Redundancy Maximum Relevance algorithm to select the relevant variables and a random forest for the classification of events. The analysis has been developed using IceCube data from the 59-string configuration of the detector. 27,771 neutrino candidates were detected in 346 days of livetime. A rejection of 99.9999 % of the atmospheric muon background is achieved. The energy spectrum of the atmospheric neutrino flux is obtained using the TRUEE unfolding program. The unfolded spectrum of atmospheric muon neutrinos covers an energy range from 100 GeV to 1 PeV. Compared to the previous measurement using the detector in the 40-string configuration, the analysis presented here, extends the upper end of the atmospheric neutrino spectrum by more than a factor of two, reaching an energy region that has not been previously accessed by spectral measurements.
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| 3. |
- Aartsen, M. G., et al.
(författare)
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Search for Prompt Neutrino Emission from Gamma-Ray Bursts with IceCube
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 805:1
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Tidskriftsartikel (refereegranskat)abstract
- We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gammaray bursts (GRBs). A single low-significance neutrino, compatible with the atmospheric neutrino background, was found in coincidence with one of the 506 observed bursts. Although GRBs have been proposed as candidate sources for ultra-high-energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than similar to 1% of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites.
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| 4. |
- 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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| 5. |
- Christoforo, M. Greyson, et al.
(författare)
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Transient response of organo-metal-halide solar cells analyzed by time-resolved current-voltage measurements
- 2015
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Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 2:4, s. 1101-1115
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Tidskriftsartikel (refereegranskat)abstract
- The determination of the power conversion efficiency of solar cells based on organo-metal-halides is subject to an ongoing debate. As solar cell devices may exhibit very slow transient response, current-voltage scans in different directions may not be congruent, which is an effect often referred to as hysteresis. We here discuss time-resolved current-voltage measurements as a means to evaluate appropriate delay times (voltage settling times) to be used in current-voltage measurements of solar cells. Furthermore, this method allows the analysis of transient current response to extract time constants that can be used to compare characteristic differences between devices of varying architecture types, selective contacts and changes in devices due to storage or degradation conditions.
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| 6. |
- Dagar, Janardan, et al.
(författare)
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Alkali Salts as Interface Modifiers in n-i-p Hybrid Perovskite Solar Cells
- 2019
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Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 3:9
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Tidskriftsartikel (refereegranskat)abstract
- After demonstration of a 23% power conversion efficiency, a high operational stability is the next most important scientific and technological challenge in perovskite solar cells (PSCs). A potential failure mechanism is tied to a bias-induced ion migration, which causes current–voltage hysteresis and a decay in the device performance over time. Herein, alkali salts are shown to mitigate hysteresis and stabilize device performance in n-i-p hybrid planar PSCs. Different alkali salts of potassium chloride, iodide, and nitrate as well as sodium chloride and iodide are deposited from aqueous solution onto the n-type contact, based on SnO2, prior to deposition of the perovskite absorber Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3. Introduction of potassium-based alkali salts suppresses the current–voltage hysteresis and stabilizes the operational device stability at the maximum power point. This is attributed to the suppression of hole trapping at the n-type selective transport layer (SnO2)/perovskite interface observed by surface photovoltage spectroscopy, which is interpreted to reduce interfacial recombination and improve charge carrier extraction. The best and most stable performance of 19% is achieved using potassium nitrate as the interface modifier. Devices with higher and more stable performance exhibit substantially lower current transients, analyzed during maximum power point tracking.
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| 7. |
- Dagar, Janardan, et al.
(författare)
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Compositional and Interfacial Engineering Yield High-Performance and Stable p-i-n Perovskite Solar Cells and Mini-Modules
- 2021
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Ingår i: ACS applied materials & interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:11, s. 13022-13033
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Tidskriftsartikel (refereegranskat)abstract
- Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p-i-n-type perovskite solar cell (PSC) with a 22.3% power conversion efficiency (PCE). This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a synergy between (1) an improved perovskite absorber quality when introducing formamidinium chloride (FACl) as an additive in the "triple cation" Cs0.05FA0.79MA0.16PbBr0.51I2.49 (Cs-MAFA) perovskite precursor ink, (2) an increased open-circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride (LiF) interfacial buffer layer, and (3) high-quality hole-selective contacts with a self-assembled monolayer (SAM) of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current-density voltage, J-V, measurements, substantial differences in device performance become apparent when considering longer-term stability data. A reduced long-term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal-halide perovskite thin-film deposition. Optimized devices maintained about 80% of the initial average PCE during maximum power point (MPP) tracking for >700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series-interconnected mini-modules with a PCE of 19.4% for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large-area single junction and tandem modules based on PSCs.
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| 8. |
- Dagar, Janardan, et al.
(författare)
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Stability assessment of p-i-n perovskite photovoltaic mini-modules utilizing different top metal electrodes
- 2021
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Ingår i: Micromachines. - : MDPI AG. - 2072-666X. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- Long-term stability is one of the major challenges for p-i-n type perovskite solar modules (PSMs). Here, we demonstrate the fabrication of fully laser-patterned series interconnected p-i-n perovskite mini-modules, in which either single Cu or Ag layers are compared with Cu/Au metalbilayer top electrodes. According to the scanning electron microscopy measurements, we found that Cu or Ag top electrodes often exhibit flaking of the metal upon P3 (top contact removal) laser patterning. For Cu/Au bilayer top electrodes, metal flaking may cause intermittent short-circuits between interconnected sub-cells during operation, resulting in fluctuations in the maximum power point (MPP). Here, we demonstrate Cu/Au metal-bilayer-based PSMs with an efficiency of 18.9% on an active area of 2.2 cm2 under continuous 1-sun illumination. This work highlights the importance of optimizing the top-contact composition to tackle the operational stability of mini-modules, and could help to improve the feasibility of large-area module deployment for the commercialization of perovskite photovoltaics.
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| 9. |
- Dobrovolsky, Alexander, et al.
(författare)
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Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.
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| 10. |
- Dobrovolsky, Alexander, et al.
(författare)
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Relating Defect Luminescence and Nonradiative Charge Recombination in MAPbI3 Perovskite Films
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:5, s. 1714-1720
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Tidskriftsartikel (refereegranskat)abstract
- Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. We applied multispectral PL imaging to samples prepared by two different procedures and exhibiting 1 order of magnitude different PL quantum yield (PLQY). The high-PLQY sample showed concentration of the emitting defect sites around 1012-1013 cm-3. No correlation between PLQY and the relative intensity of the defect emission was found when micrometer-sized local regions of the same sample were compared. However, a clear positive correlation between the lower PLQY and higher defect emission was observed when two preparation methods were contrasted. Therefore, although the emissive defects are not connected directly with the nonradiative centers and may be spatially separated at the nano scale, chemical processes during the perovskite synthesis promote/prevent formation of both types of defects at the same time.
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