Laser Printing of Multilayered Alternately Conducting and Insulating Microstructures

Production of multilayered microstructures composed of conducting and insulating materials is of great interest as they can be utilized as microelectronic components. Current proposed fabrication methods of these microstructures include top-down and bottom-up methods, each having their own set of drawbacks. Laser-based methods were shown to pattern various materials with micron/sub-micron resolution; however, multilayered structures demonstrating conducting/insulating/conducting properties were not yet realized. Here, we demonstrate laser printing of multilayered microstructures consisting of conducting platinum and insulating silicon oxide layers by a combination of thermally driven reactions with microbubble-assisted printing. PtCl2 dissolved in N-methyl-2-pyrrolidone (NMP) was used as a precursor to form conducting Pt layers, while tetraethyl orthosilicate dissolved in NMP formed insulating silicon oxide layers identified by Raman spectroscopy. We demonstrate control over the height of the insulating layer between ∼50 and 250 nm by varying the laser power and number of iterations. The resistivity of the silicon oxide layer at 0.5 V was 1.5 × 1011 ωm. Other materials that we studied were found to be porous and prone to cracking, rendering them irrelevant as insulators. Finally, we show how microfluidics can enhance multilayered laser microprinting by quickly switching between precursors. The concepts presented here could provide new opportunities for simple fabrication of multilayered microelectronic devices

Broad Band Photometric Reverberation Mapping of NGC 4395

We present results of broad band photometric reverberation mapping (RM) to measure the radius of the broad line region, and subsequently the black hole mass (M$_{\rm BH}$), in the nearby, low luminosity active galactic nuclei (AGN) NGC 4395. Using the Wise Observatory's 1m telescope equipped with the SDSS g$'$, r$'$ and i$'$ broad band filters, we monitored NGC 4395 for 9 consecutive nights and obtained 3 light curves each with over 250 data points. The g$'$ and r$'$ bands include time variable contributions from H$\beta$ and H$\alpha$ (respectively) plus continuum. The i$'$ band is free of broad lines and covers exclusively continuum. We show that by looking for a peak in the difference between the cross-correlation and the auto-correlation functions for all combinations of filters, we can get a reliable estimate of the time lag necessary to compute M$_{\rm BH}$. We measure the time lag for H$\alpha$ to be $3.6 \pm 0.8$ hours, comparable to previous studies using the line resolved spectroscopic RM method. We argue that this lag implies a black hole mass of M$_{\rm BH} = (4.9 \pm 2.6) \times 10^{4}$ \Msun

Preparation of Single-Phase Films of CH3NH3Pb(I1-xBrx)3 with Sharp Optical Band Edges.

Organometallic lead-halide perovskite-based solar cells now approach 18% efficiency. Introducing a mixture of bromide and iodide in the halide composition allows tuning of the optical bandgap. We prepare mixed bromide-iodide lead perovskite films CH3NH3Pb(I1-xBrx)3 (0 ≤ x ≤ 1) by spin-coating from solution and obtain films with monotonically varying bandgaps across the full composition range. Photothermal deflection spectroscopy, photoluminescence, and X-ray diffraction show that following suitable fabrication protocols these mixed lead-halide perovskite films form a single phase. The optical absorption edge of the pure triiodide and tribromide perovskites is sharp with Urbach energies of 15 and 23 meV, respectively, and reaches a maximum of 90 meV for CH3NH3PbI1.2Br1.8. We demonstrate a bromide-iodide lead perovskite film (CH3NH3PbI1.2Br1.8) with an optical bandgap of 1.94 eV, which is optimal for tandem cells of these materials with crystalline silicon devices.We acknowledge funding from the Engineering and Physical Sciences Research Council (EPSRC) and the Winton Programme (Cambridge) for the Physics of Sustainability. THT acknowledges funding from Cambridge Australia Scholarships and the Cambridge Commonwealth Trust. D.C. acknowledges support from St. John's College Cambridge and the Winton Programme (Cambridge) for the Physics of Sustainability.This is the final published version. It's also available at: http://pubs.acs.org/doi/abs/10.1021/jz501332v

Measuring the mass of the central black hole in the bulgeless galaxy ngc 4395 from gas dynamical modeling

NGC 4395 is a bulgeless spiral galaxy, harboring one of the nearest known type 1 Seyfert nuclei. Although there is no consensus on the mass of its central engine, several estimates suggest it is one of the lightest massive black holes (MBHs) known. We present the first direct dynamical measurement of the mass of this MBH from a combination of two-dimensional gas kinematic data, obtained with the adaptive optics assisted near-infrared integral field spectrograph Gemini/NIFS and high-resolution multiband photometric data from Hubble Space Telescope's Wide Field Camera 3. We use the photometric data to model the shape and stellar mass-to-light ratio of the nuclear star cluster (NSC). From the Gemini/NIFS observations, we derive the kinematics of warm molecular hydrogen gas as traced by emission through the H2 1–0 S(1) transition. These kinematics show a clear rotational signal, with a position angle orthogonal to NGC 4395's radio jet. Our best-fitting tilted ring models of the kinematics of the molecular hydrogen gas contain a black hole with mass M={4}-3+8× {10}5 M⊙ (3σ uncertainties) embedded in an NSC of mass M=2× {10}6 M⊙. Our black hole mass measurement is in excellent agreement with the reverberation mapping mass estimate of Peterson et al. but shows some tension with other mass measurement methods based on accretion signals

Understanding how excess lead iodide precursor improves halide perovskite solar cell performance

The presence of excess lead iodide in halide perovskites has been key for surpassing 20% photon-to-power conversion efficiency. To achieve even higher power conversion efficiencies, it is important to understand the role of remnant lead iodide in these perovskites. To that end, we explored the mechanism facilitating this effect by identifying the impact of excess lead iodide within the perovskite film on charge diffusion length, using electron-beam-induced current measurements, and on film formation properties, from grazing-incidence wide-angle X-ray scattering and high-resolution transmission electron microscopy. Based on our results, we propose that excess lead iodide in the perovskite precursors can reduce the halide vacancy concentration and lead to formation of azimuthal angle-oriented cubic alpha-perovskite crystals in-between 0 degrees and 90 degrees. We further identify a higher perovskite carrier concentration inside the nanostructured titanium dioxide layer than in the capping layer. These effects are consistent with enhanced lead iodide-rich perovskite solar cell performance and illustrate the role of lead iodide

The Swift Surge of Perovskite Photovoltaics

The breakthrough early 1990s dye sensitization of mesoscopic TiO2 films along with a regenerative iodide redox couple led to the explosive growth of dye-sensitized solar cell (DSC) research. The pioneering work of Grätzel and colleagues also made it possible to develop a solid-state DSSC with spiro-oMETAD as the hole conductor and thus replace the liquid electrolyte in the cell. Research efforts of Konenkamp and others further initiated the search for the “extremely thin absorber” (ETA) nanostructured solar cell, using TiO2 as the electron conductor, an inorganic absorber, and a hole conductor. Another major research thrust was by Weller, Kamat, Zaban, Nozik, Hodes, and others, who employed inorganic quantum dots (e.g., CdS and CdSe) as sensitizers. While discussing developments in sensitized solar cells, it is important to note the contributions of early visionaries like Gerischer, Sutin, and Bard, who were first to establish the concepts of sensitization using dye molecules and semiconductor nanostructures

Spectral splitting photovoltaics using perovskite and wideband dye-sensitized solar cells

The extension of the light absorption of photovoltaics into the near-infrared region is important to increase the energy conversion efficiency. Although the progress of the lead halide perovskite solar cells is remarkable, and high conversion efficiency of >20% has been reached, their absorption limit on the long-wavelength side is similar to 800 nm. To further enhance the conversion efficiency of perovskite-based photovoltaics, a hybridized system with near-infrared photovoltaics is a useful approach. Here we report a panchromatic sensitizer, coded DX3, that exhibits a broad response into the near-infrared, up to similar to 1100 nm, and a photocurrent density exceeding 30 mA cm(-2) in simulated air mass 1.5 standard solar radiation. Using the DX3-based dye-sensitized solar cell in conjunction with a perovskite cell that harvests visible light, the hybridized mesoscopic photovoltaics achieved a conversion efficiency of 21.5% using a system of spectral splitting.open0

Enhanced optoelectronic quality of perovskite thin films with hypophosphorous acid for planar heterojunction solar cells

Solution-processed metal halide perovskite semiconductors, such as CH3NH3PbI3, have exhibited remarkable performance in solar cells, despite having non-negligible density of defect states. A likely candidate is halide vacancies within the perovskite crystals, or the presence of metallic lead, both generated due to the imbalanced I/Pb stoichiometry which could evolve during crystallization. Herein, we show that the addition of hypophosphorous acid (HPA) in the precursor solution can significantly improve the film quality, both electronically and topologically, and enhance the photoluminescence intensity, which leads to more efficient and reproducible photovoltaic devices. We demonstrate that the HPA can reduce the oxidized I2 back into I�, and our results indicate that this facilitates an improved stoichiometry in the perovskite crystal and a reduced density of metallic lead

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)