Low-Cost Flexible Nano-Sulfide/Carbon Composite Counter Electrode for Quantum-Dot-Sensitized Solar Cell

Cu2S nanocrystal particles were in situ deposited on graphite paper to prepare nano-sulfide/carbon composite counter electrode for CdS/CdSe quantum-dot-sensitized solar cell (QDSC). By optimization of deposition time, photovoltaic conversion efficiency up to 3.08% was obtained. In the meantime, this composite counter electrode was superior to the commonly used Pt, Au and carbon counter electrodes. Electrochemical impedance spectra further confirmed that low charge transfer resistance at counter electrode/electrolyte interface was responsible for this, implied the potential application of this composite counter electrode in high-efficiency QDSC

The violent youth of bright and massive cluster galaxies and their maturation over 7 billion years

In this study, we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift (z ∼ 0.9), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift (z ∼ 0.1) counterparts drawn from the MCXC meta-catalogue, supplemented by Sloan Digital Sky Survey imaging and spectroscopy. We observed striking differences in the morphological, colour, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broad-band colours, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of 2.51 ± 0.71 from z ∼ 0.9 to z ∼ 0.1. Through this and other comparisons, we conclude that a combination of major merging (mainly wet or mixed) and in situ star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of ∼3, while their average Sérsic index increased by ∼0.45 from z ∼ 0.9 to z ∼ 0.1, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past ∼7 Gyr

Mechanism of carrier accumulation in perovskite thin-absorber solar cells

[EN] Photovoltaic conversion requires two successive steps: accumulation of a photogenerated charge and charge separation. Determination of how and where charge accumulation is attained and how this accumulation can be identified is mandatory for understanding the performance of a photovoltaic device and for its further optimization. Here we analyse the mechanism of carrier accumulation in lead halide perovskite, CH3NH3PbI3, thin-absorber solar cells by means of impedance spectroscopy. A fingerprint of the charge accumulation in high density of states of the perovskite absorber material has been observed at the capacitance of the samples. This is, as far as we know, the first observation of charge accumulation in light-absorbing material for nanostructured solar cells, indicating that it constitutes a new kind of photovoltaic device, differentiated from sensitized solar cells, which will require its own methods of study, characterization and optimization.We thank the following agencies for supporting this research: Ministerio de Educacion y Ciencia under project HOPE CSD2007-00007, Generalitat Valenciana (ISIC/2012/008) and Universitat Jaume I project 12I361.01/1. This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT & Future Planning (MSIP) of Korea under contracts No. NRF-2012M1A2A2671721, NRF-2010-0014992 and NRF-2012M3A6A7054861 (the Global Frontier R&D Program on Center for Multiscale Energy System). H.-S.K. is grateful for the global Ph.D. fellowship grant funded by NRF (NRF-2011-0008467). We thank Mr. Dae-Yong Son for preparation of the ZrO2 paste. We thank Prof. A. Maquieira and Dr. M.J. Banuls from the Institute of Molecular Recognition and Technological Development (Polytechnic University of Valencia) for SEM measurements of CH3NH3PbI3-xClx samples.Kim, H.; Mora-Sero, I.; González-Pedro, V.; Fabregat-Santiago, F.; Juarez-Perez, EJ.; Park, N.; Bisquert Mascarell, J. (2013). Mechanism of carrier accumulation in perovskite thin-absorber solar cells. Nature Communications. 4:1-7. https://doi.org/10.1038/ncomms3242S174Nozik, A. J. Quantum dot solar cells. Physica E 14, 115–200 (2002).O'Regan, B. & Gratzel, M. A low-cost, high-efficiency solar-cell based on dye-sensitized colloidal TiO2 films. Nature 353, 737–740 (1991).Hodes, G. Comparison of dye- and semiconductor-sensitized porous nanocrystalline liquid junction solar cells. J. Phys. Chem. C 112, 17778–17787 (2008).Mora-Seró, I. & Bisquert, J. Breakthroughs in the development of semiconductor-sensitized solar cells. J. Phys. Chem. Lett. 1, 3046–3052 (2010).Kim, H.-S. et al. Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%. Sci. Rep. 2, 591 (2012).Lee, M. M., Teuscher, J., Miyasaka, T., Murakami, T. N. & Snaith, H. J. Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science 338, 643–647 (2012).Noh, J. H., Im, S. H., Heo, J. H., Mandal, T. N. & Seok, S. I. Chemical management for colorful, efficient, and stable inorganic–organic hybrid nanostructured solar cells. Nano. Lett. 13, 1764–1769 (2013).Ball, J. M., Lee, M. M., Hey, A. & Snaith, H. Low-temperature processed mesosuperstructured to thin-film perovskite solar cells. Energy Environ. Sci. 6, 1739–1743 (2013).Edri, E., Kirmayer, S., Cahen, D. & Hodes, G. High open-circuit voltage solar cells based on organic–inorganic lead bromide perovskite. J. Chem. Phys. Lett. 4, 897–902 (2013).Im, J.-H., Lee, C.-R., Lee, J.-W., Park, S.-W. & Park, N.-G. 6.5% efficient perovskite quantum-dot-sensitized solar cell. Nanoscale 3, 4088–4093 (2011).Kojima, A., Teshima, K., Shirai, Y. & Miyasaka, T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem. Soc. 131, 6050–6051 (2009).Etgar, L. et al. Mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cells. J. Am. Chem. Soc. 134, 17396–17399 (2012).Hod, I. et al. Dye versus quantum dots in sensitized solar cells: participation of quantum dot absorber in the recombination process. J. Phys. Chem. Lett. 2, 3032–3035 (2011).Boix, P. P. et al. From flat to nanostructured photovoltaics: balance between thickness of the absorber and charge screening in sensitized solar cells. ACS Nano 6, 873–880 (2012).Unger, E. L. et al. Bilayer hybrid solar cells based on triphenylamine-thienylenevinylene dye and TiO2 . J. Phys. Chem. C 114, 11659–11664 (2010).Palomares, E., Clifford, J. N., Haque, S. A., Lutz, T. & Durrant, J. R. Control of charge recombination dynamics in dye sensitized solar cells by the use of conformally deposited metal oxide blocking layers. J. Am. Chem. Soc. 125, 475–482 (2003).Topoglidis, E., Campbell, C. J., Palomares, E. & Durrant, J. R. Photoelectrochemical study of Zn cytochrome-c immobilised on a nanoporous metal oxide electrode. Chem. Comm. 14, 1518–1519 (2002).Bisquert, J. Chemical capacitance of nanostructured semiconductors: its origin and significance for nanocomposite solar cells. Phys. Chem. Chem. Phys. 5, 5360–5364 (2003).Fabregat-Santiago, F., Garcia-Belmonte, G., Mora-Seró, I. & Bisquert, J. Characterization of nanostructured hybrid and organic solar cells by impedance spectroscopy. Phys. Chem. Chem. Phys. 13, 9083–9118 (2011).Bisquert, J., Grätzel, M., Wang, Q. & Fabregat-Santiago, F. Three-channel transmission line impedance model for mesoscopic oxide electrodes functionalized with a conductive coating. J. Chem. Phys. B 110, 11284–11290 (2006).Bisquert, J. Theory of the impedance of electron diffusion and recombination in a thin layer. J. Chem. Phys. B 106, 325–333 (2002).Fabregat-Santiago, F. et al. Electron transport and recombination in solid-state dye solar cell with Spiro-OMeTAD as hole conductor. J. Am. Chem. Soc. 131, 558–562 (2009).Dualeh, A., Moehl, T., Nazeeruddin, M. K. & Grätzel, M. Temperature dependence of transport properties of Spiro-MeOTAD as a hole transport material in solid-state dye-sensitized solar cells. ACS Nano 7, 2292–2301 (2013).Fabregat-Santiago, F., Garcia-Belmonte, G., Bisquert, J., Bogdanoff, P. & Zaban, A. Mott-Schottky analysis of nanoporous semiconductor electrodes in the dielectric state deposited on SnO2(F) conducting substrates. J Electrochem. Soc. 150, E293–E298 (2002).Kim, M.-J. et al. Unusual enhancement of photocurrent by incorporation of bronsted base thiourea into electrolyte of dye-sensitized solar cell. J. Chem. Phys. C 114, 19849–19852 (2010).Ito, S. et al. Photovoltaic characterization of dye-sensitized solar cells: effect of device masking on conversion efficiency. Prog. Photovolt: Res. Appl. 14, 589–601 (2006)

Impact of COVID-19 infection on the outcome of patients with ischemic stroke

BACKGROUND AND PURPOSE: We evaluated whether stroke severity, functional outcome, and mortality are different in patients with ischemic stroke with or without coronavirus disease 2019 (COVID-19) infection. METHODS: A prospective, observational, multicentre cohort study in Catalonia, Spain. Recruitment was consecutive from mid-March to mid-May 2020. Patients had an acute ischemic stroke within 48 hours and a previous modified Rankin Scale (mRS) score of 0 to 3. We collected demographic data, vascular risk factors, prior mRS score, National Institutes of Health Stroke Scale score, rate of reperfusion therapies, logistics, and metrics. Primary end point was functional outcome at 3 months. Favourable outcome was defined depending on the previous mRS score. Secondary outcome was mortality at 3 months. We performed mRS shift and multivariable analyses. RESULTS: We evaluated 701 patients (mean age 72.3±13.3 years, 60.5% men) and 91 (13%) had COVID-19 infection. Median baseline National Institutes of Health Stroke Scale score was higher in patients with COVID-19 compared with patients without COVID-19 (8 [3–18] versus 6 [2–14], P=0.049). Proportion of patients with a favourable functional outcome was 33.7% in the COVID-19 and 47% in the non-COVID-19 group. However, after a multivariable logistic regression analysis, COVID-19 infection did not increase the probability of unfavourable functional outcome. Mortality rate was 39.3% among patients with COVID-19 and 16.1% in the non-COVID-19 group. In the multivariable logistic regression analysis, COVID-19 infection was a risk factor for mortality (hazard ratio, 3.14 [95% CI, 2.10–4.71]; P<0.001). CONCLUSIONS: Patients with ischemic stroke and COVID-19 infection have more severe strokes and a higher mortality than patients with stroke without COVID-19 infection. However, functional outcome is comparable in both groups

Properties of Electrodeposited CuSCN 2D Layers and Nanowires Influenced by Their Mixed Domain Structure

International audienc

Energy transfer versus charge separation in hybrid systems of semiconductor quantum dots and Ru-dyes as potential co-sensitizers of TiO2-based solar cells.

Hybrid structures of colloidal quantum dots (QDs) with Ru-dyes have been studied as candidates for panchromatic sensitizers for TiO2-based solar cells. Steady-state and time resolved photoluminescence spectroscopy and photocurrent measurements have been employed to identify the prevailing transfer mechanisms for photogenerated excitons between CdSe QDs capped with a traditional bulky organic ligand trioctylphosphine and Ru-dyes (N3 or Ru505) deposited onto inert glass or mesoporous TiO2 substrates. The type II energy level alignment between the QDs and both N3 and Ru505 offers a possibility for the directional charge separation, with electrons transferred to the QDs and holes to the dye. This scenario is indeed valid for the QD/Ru505 and TiO2/QD/Ru505 hybrid systems, with the negligible spectral overlap between the emission of the QDs and the absorption of the Ru505 dye. For the QD/N3 and TiO2/QD/N3 hybrid systems, the spectral overlap favors the longer range energy transfer from the QDs to N3, independently of the presence of the electron acceptor TiO2