| 1. |
- Wang, Xin, et al.
(författare)
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Organic nanocrystals induced surface passivation towards high-efficiency and stable perovskite solar cells
- 2021
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Ingår i: Nano Energy. - : ELSEVIER. - 2211-2855 .- 2211-3282. ; 89
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Tidskriftsartikel (refereegranskat)abstract
- Surface passivation has played a critical role for efficient and stable perovskite solar cells by reducing surface defects, promoting charge transport, and preventing the penetration of degrading agents. State-of-the-art passivation approaches mainly rely on the formation of a two-dimensional (2D) perovskite layer or the deposition of an ultrathin layer based on the molecular design. Here, we demonstrated a novel nanocrystal-pinning passivation by dripping 2-bromoethyltrimethylammonium bromide (BETAB) colloidal solution onto perovskite films. Theoretical simulation and kinds of experimental results confirm that BETAB nanocrystals can effectively reduce the defect density of perovskite films. Impressively, the resulting FA1-xMAxPbI3 based planar devices exhibit a champion power conversion efficiency (PCE) of 23.04% (certified: 22.10%) with a voltage loss of only 390 mV. Besides, the BETAB nanocrystals could simultaneously increase the hydrophobic property of perovskite films and prevent the reaction and formation of 2D perovskites during device operation. Correspondingly, the resulted devices exhibit excellent stability under moisture, heating, and operational tracking conditions.
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| 2. |
- Yang, Hengyan, et al.
(författare)
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New Understanding on Photocatalytic Mechanism of Nitrogen-Doped Graphene Quantum Dots-Decorated BiVO4 Nanojunction Photocatalysts
- 2017
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 2:7, s. 3766-3773
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Tidskriftsartikel (refereegranskat)abstract
- Bismuth vanadate (BiVO4) is a promising candidate as a visible-light-driven photocatalyst in the aspect of practical applications. To investigate the origin of active species from BiVO4 and understand the influence of the variations of the photocatalytic process, comparative studies on zero-dimensional nitrogen-doped graphene quantum dot (NGQD)-decorated BiVO4 have been carried out for methylene blue photodegradation. It was found that the hydroxyl group-rich NGQD surface and the established heterojunction structure between NGQDs and BiVO4 were greatly beneficial for the conversion of the MOH radical. With NGQD decoration, the dominant oxidant species for NGQDs/BiVO4 were confirmed to be MOH and H2O2, rather than holes originating from the valence band of unmodified BiVO4. The synergistic photocatalytic mechanism with respect to the interfacial charge transport and the conversion of active species was proposed. The achievement of the controllable active species significantly altering the activity may be applied for different photocatalytic reactions.
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| 3. |
- Luo, Jiaxin, et al.
(författare)
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Solar cells sensitized by donor-linked concerted companion dyes
- 2023
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 11:16, s. 5450-5460
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Tidskriftsartikel (refereegranskat)abstract
- Recently, concerted companion (CC) dyes have been developed by covalently linking the acceptors of organic and porphyrin dye units. Herein, a new class of CC dyes XW85 and XW86 have been designed by linking the donors of porphyrin and organic dye units with C6H12 and C12H24 chains, respectively. The DSSCs of XW85 based on the I-3(-)/I- electrolyte show significant J(SC) (17.20 mA cm(-2)) and PCE (8.96%), and XW86 exhibits higher J(SC) (18.55 mA cm(-2)) and PCE (9.76%), which are also higher than those of the corresponding cosensitization systems. However, the PCEs for XW85 and XW86 are lower than that of the acceptor-linked reference dye XW76 despite the obviously larger dye adsorption amounts. Desorption studies reveal that the CC dyes may be either double-anchored or single-anchored, with the double/single anchoring ratios lying in a sequence of XW85 (1.31) < XW86 (1.88) < XW76 (6.34), consistent with that of increasing PCE. These observations indicate that the non-adsorbed sub-dye unit cannot effectively contribute to electron injection, and thus relatively large mono-anchoring proportions for XW85 and XW86 result in their relatively low J(SC), and the difference between XW85 and XW86 indicates that a longer linking chain is beneficial for partially alleviating the unfavorable single anchoring, resulting in superior performance. The results indicate that the photovoltaic behavior for the CC dyes may be further enhanced by avoiding the unfavorable alignment of the two carboxyl groups in opposite directions and thus simultaneously anchoring the two carboxyl groups, which may be realized through more rational molecular design.
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| 4. |
- Anderson, Marin M., et al.
(författare)
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Simultaneous Search for Prompt Radio Emission Associated with the Short GRB 170112A Using the All-sky Imaging Capability of the OVRO-LWA
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 864:1
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Tidskriftsartikel (refereegranskat)abstract
- We have conducted the most sensitive low-frequency (below 100 MHz) search to date for prompt, low-frequency radio emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field of view (similar to 20,000 square degrees) allows us to search for low-frequency (sub-100 MHz) counterparts for a large sample of the subset of GRB events for which prompt radio emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source to within a 3 sigma flux density limit of 4.5. Jy at 13 s timescales for frequencies spanning 27-84. MHz. We place constraints on a number of models predicting prompt, low-frequency radio emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of L-radio/L gamma less than or similar to 3.5 x 10(-6) on the fraction of energy released in the prompt radio emission, under the assumptions of negligible scattering of the radio pulse and beaming of emission along the line of sight. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements that are critical to placing constraining limits on prompt radio emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.
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| 5. |
- Bellm, Eric C., et al.
(författare)
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An Optically Discovered Outburst from XTE J1859+226
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 956:1
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Tidskriftsartikel (refereegranskat)abstract
- Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the black hole X-ray transient XTE J1859+226 since its discovery in 1999. The outburst was visible at X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its full outburst of 320 days in 1999, and the observed peak luminosity was 2 orders of magnitude lower. Its peak bolometric luminosity was only 2 × 1035 erg s−1, implying an Eddington fraction of about 3 × 10−4. The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 1011 cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray light curve. These observations highlight the potential of optical and infrared synoptic surveys to discover low-luminosity activity from X-ray transients.
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| 6. |
- Eastwood, Michael W., et al.
(författare)
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The Radio Sky at Meter Wavelengths: M-mode Analysis Imaging with the OVRO-LWA
- 2018
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 156:1
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Tidskriftsartikel (refereegranskat)abstract
- A host of new low-frequency radio telescopes seek to measure the 21 cm transition of neutral hydrogen from the early universe. These telescopes have the potential to directly probe star and galaxy formation at redshifts 20 ≳ z ≳ 7 but are limited by the dynamic range they can achieve against foreground sources of low-frequency radio emission. Consequently, there is a growing demand for modern, high-fidelity maps of the sky at frequencies below 200 MHz for use in foreground modeling and removal. We describe a new wide-field imaging technique for drift-scanning interferometers: Tikhonov-regularized m-mode analysis imaging. This technique constructs images of the entire sky in a single synthesis imaging step with exact treatment of wide-field effects. We describe how the CLEAN algorithm can be adapted to deconvolve maps generated by m-mode analysis imaging. We demonstrate Tikhonov-regularized m-mode analysis imaging using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) by generating eight new maps of the sky north of δ = -30° with 15′ angular resolution at frequencies evenly spaced between 36.528 and 73.152 MHz and ∼800 mJy beam-1thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions ≥2°. Each map is constructed exclusively from interferometric observations and does not represent the globally averaged sky brightness. Future improvements will incorporate total power radiometry, improved thermal noise, and improved angular resolution due to the planned expansion of the OVRO-LWA to 2.6 km baselines. These maps serve as a first step on the path to the use of more sophisticated foreground filters in 21 cm cosmology incorporating the measured angular and frequency structure of all foreground contaminants.
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| 7. |
- Wang, Xiaolong, et al.
(författare)
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Carrier Frequency Offset Estimation in the Presence of I/Q Mismatch for Wideband OFDM Systems
- 2012
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Ingår i: IEEE 55th International Midwest Symposium on Circuits and Systems (MWSCAS), 2012. - 9781467325264 ; , s. 924-927
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Konferensbidrag (refereegranskat)abstract
- This paper presents a data-aided Carrier Frequency Offset (CFO) estimation algorithm targeting the Wideband OFDM systems. Utilizing 3 consecutive preambles and processing them at frequency domain, the algorithm is robust to both Frequency Independent (F-I) and Frequency Dependent (F-D) I/Q Mismatch (I/Q-M). To evaluate the effectiveness of the proposed CFO estimation technique, we conduct extensive simulations based on Multi-Band OFDM Ultra-Wide Band wireless transmission. Compared to the ideal case when the CFO has been perfectly estimated, the performance loss at 8% Packet Error Rate (PER) is less than 0.5 dB.
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