N-type emitters passivation through antireflective phosphorus doped a-SiCxNy:H(n) stacks

This paper studies the passivation of industrially textured deep silicon emitters using amorphous silicon carbonitride layers in stack configuration, deposited by plasma enhanced chemical vapor deposition. With this technique, emitter saturation current density can be decreased to values around 250 fA middot cm-2. As a consequence, open circuit voltages can be increased 25 mV achieving values around 640 mV.Postprint (published version

Integrated Flight and Propulsion Control for Novel Rotorcraft

Distributed Electric Propulsion (DEP) has increased the design space for aerospace vehicles, especially those categorized as eVTOL (Electric Vertical Take-Off and Landing). This new class of vehicles not only looks different from the typical airplane or helicopter, but functions differently as well. A robust understanding of how the vehicle is controlled in both nominal and off-nominal modes will frame the approach to certification for private and commercial VTOL aircraft. Embry-Riddle Aeronautical University’s Eagle Flight Research Center (EFRC) is researching how the various methods of DEP thrust control apply to larger eVTOL vehicle operation. Researchers will utilize a mixture of flight dynamic simulation and physical testing in collaboration with FAA experts in rotorcraft handling qualities certification. Outcomes of the research include the characterization of various DEP thrust and moment control methods and how this maps to certifiable vehicle-level attributes like handling qualities in nominal and degraded flight modes. A prototype will be built and tested showing the ability of a quad-rotor vehicle to continue flight after the loss of thrust by failure of one rotor. It is anticipated that a better understanding of the DEP units will help inform the process of certification for the emerging market of urban air mobility vehicles. The data obtained from testing will be utilized to define the possible performance parameters, which will aid in developing appropriate means of compliance for advanced fly-by-wire N-rotor eVTOL vehicles

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J-V Hysteresis

Methylammonium lead iodide (MAPI) cells of the design FTO/sTiO2/ mpTiO2/MAPI/Spiro-OMeTAD/Au, where FTO is fluorine-doped tin oxide, sTiO2 indicates solid-TiO2, and mpTiO2 is mesoporous TiO2, are studied using transient photovoltage (TPV), differential capacitance, charge extraction, current interrupt, and chronophotoamperometry. We show that in mpTiO2/MAPI cells there are two kinds of extractable charge stored under operation: a capacitive electronic charge (&sim;0.2 &mu;C/ cm2) and another, larger charge (40 &mu;C/cm2), possibly related to mobile ions. Transient photovoltage decays are strongly double exponential with two time constants that differ by a factor of &sim;5, independent of bias light intensity. The fast decay (&sim;1 &mu;s at 1 sun) is assigned to the predominant charge recombination pathway in the cell. We examine and reject the possibility that the fast decay is due to ferroelectric relaxation or to the bulk photovoltaic effect. Like many MAPI solar cells, the studied cells show significant J&minus;V hysteresis. Capacitance vs open circuit voltage (Voc) data indicate that the hysteresis involves a change in internal potential gradients, likely a shift in band offset at the TiO2/MAPI interface. The TPV results show that the Voc hysteresis is not due to a change in recombination rate constant. Calculation of recombination flux at Voc suggests that the hysteresis is also not due to an increase in charge separation efficiency and that charge generation is not a function of applied bias. We also show that the J&minus;V hysteresis is not a light driven effect but is caused by exposure to electrical bias, light or dark.</div

Interferometric study of microchamber in large area dye solar cells

Dye-sensitized solar cells (DSCs) have a typical sandwich structure, with the active layers between two conductive glass sheets. Their co-planarity could be an issue in the mass production of large area devices. The micrometric gap should be uniform all over the device, in order to maintain a good electrolyte layer. The frames of sealant, which isolate the adjacent cells in a module, usually work also as spacers. Nevertheless, the uniformity of the gap is not commonly tested in a systematic way. Here large area empty blanks and full DSCs were studied by means of optical interferometry, i.e., monochromatic surface scan and wavelength scan. The collected fringe patterns allowed retrieval of the microchamber’s absolute profile. In some cases, evident U-shaped bending was found, with edge-to-center variation up to Dh/h 80%. Interestingly, despite the large absorption and the weak index contrast in the full DSCs, a good fringes’ visibility was achieved, by adopting near-infrared (IR) laser source and filtering off external reflections. Moreover, the IR n and k indexes of porous titania dyed and filled with electrolyte were retrieved. In summary, the results show that the bending effect must always be tackled for large area, by using the right sealing frames and thermal treatments. Further improved IR interferometry can be successfully implemented for in-line testing of DSCs structure and uniformity

Investigating charge dynamics in halide perovskite-sensitized mesostructured solar cells

Charge generation and transport in (CH3NH3) Pbl(3-x)Cl(x) sensitized mesostructured solar cells are investigated. A highly efficient charge generation is directly proven by time correlated single photon counting analysis. Photoinduced absorption and transient photo-voltage investigations depict double charge recombination dynamics. To explain the high device performances according to those spectroscopic observations, we suggest the existence of two complementary paths for electron transport, involving either TiO2 or perovskite matrixes

A polyfluoroalkyl imidazolium ionic liquid as iodide ion source in dye sensitized solar cells

We report on the use of a fluorinated imidazolium ionic liquid as a source of iodide ions in solvent-based electrolytes for DSSCs. Efficient dye regeneration and fast charge transport in the fluorinated electrolyte result in an overall improvement of the device performances compared to conventional hydrogenated ionic liquids. © 2012 Elsevier B.V. All rights reserved

Metal-free benzodithiophene-containing organic dyes for dye-sensitized solar cells

Two new metal-free organic dyes, CR29 and CR52, with high extinction coefficients in the visible spectral region between 400\u2013650 nm, have been synthesized. The donor\u2013acceptor structure of the dyes feature benzodithiophene moieties BDT1 and BDT as rigid \u3c0-conjugated spacers, which have so far been very little studied for dye-sensitized solar cell (DSSC) applications. DFT/TDDFT calculations have been employed to guide the design of the chromophores as wellas to shed light on their electronic and optical properties. Photophysical and electrochemical characterization studies have been carried out to gather information on the charge transfer processes occurring at the dye\u2013semiconductor interfaces. Under standard AM 1.5 conditions, DSSC sensitized with CR29 showed good onversion efficiencies: 5.14% in the liquid electrolyte cell setup and 2.47% in the solid-state DSSC

Investigating charge dynamics in halide perovskite-sensitized mesostructured solar cells

Charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells are investigated. Time correlated single photon counting analysis proves highly efficient charge generation and provides insights on the structural properties of perovskite films. Photoinduced absorption and transient photovoltage analyses depict a double charge recombination dynamics suggesting the existence of two complementary paths for electron transport, involving either TiO2 and perovskite matrixes. Stark spectroscopy, a powerful tool allowing interface-sensitive analysis, is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface. This evidence is also confirmed by first principle DFT calculations. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films

Progressive ascending myelopathy: atypical forms of multiple sclerosis or what else?

The spinal cord can be affected by multiple heterogeneous disorders often difficult to diagnose. We describe ten patients affected by a progressive ascending myelopathy with a poor prognosis. The patients, during the follow-up period, underwent neurological examinations, cerebrospinal fluid analysis, hematological, microbiological, auto-antibodies screening, brain and spinal cord magnetic resonance imaging (MRI) and electroneurophysiological study. At disease onset spinal cord MRI showed 651 myelopathic lesions extended for <2 segments and then evidenced a progressive spinal cord atrophy without any new lesion. All patients showed an increase of the visual evoked potential P100 latency. All of them showed two or more clinical recurrences of myelitis and then, after a period ranging from 3 to 5 years from the disease onset, a progressive course. Five patients became unresponsive to intravenous high-dose steroid treatments and/or intravenous immunoglobulins and to any other therapeutic attempts, developed a progressive ascending myelopathy to tetraplegia and died from respiratory failure. The other five patients are in progressive phase of the disease with an initial involvement of the upper limbs and show mild cervical spinal cord atrophy at MRI, configuring the early stage of an ascending progressive myelopathy. In our opinion, the more suitable diagnosis is an atypical form of MS although is not possible to exclude a new nosological entity that could be included in the expanding range of spinal cord diseases