Dye-sensitized solar cells (DSCs) with cobalt-based mediators with efficiencies surpassing the record for DSCs with iodide-free electrolytes were developed by selecting a suitable combination of a ...cobalt polypyridine complex and an organic sensitizer. The effect of the steric properties of two triphenylamine-based organic sensitizers and a series of cobalt polypyridine redox mediators on the overall device performance in DSCs as well as on transport and recombination processes in these devices was compared. The recombination and mass-transport limitations that, previously, have been found to limit the performance of these mediators were avoided by matching the properties of the dye and the cobalt redox mediator. Organic dyes with higher extinction coefficients than the standard ruthenium sensitizers were employed in DSCs in combination with outer-sphere redox mediators, enabling thinner TiO2 films to be used. Recombination was reduced further by introducing insulating butoxyl chains on the dye rather than on the cobalt redox mediator, enabling redox couples with higher diffusion coefficients and more suitable redox potential to be used, simultaneously improving the photocurrent and photovoltage of the device. Optimization of DSCs sensitized with a triphenylamine-based organic dye in combination with tris(2,2′-bipyridyl)cobalt(II/III) yielded solar cells with overall conversion efficiencies of 6.7% and open-circuit potentials of more than 0.9 V under 1000 W m−2 AM1.5 G illumination. Excellent performance was also found under low light intensity indoor conditions.
Dye-sensitized solar cells (DSCs) with open-circuit potentials above 1 V were obtained by employing the triphenylamine based organic dye D35 in combination with cobalt phenanthroline redox couples. A ...series of cobalt bipyridine and cobalt phenanthroline complexes with different redox potentials were investigated to examine the dependence of the driving force for recombination and dye regeneration on the photovoltaic performance. The photovoltage of the devices was found to increase and the photocurrent to decrease with increasing redox potential of the complexes. The halftime for regeneration of the oxidized dye by cobalt trisbipyrine was about 20 μs, similar to that found for the iodide/triiodide redox couple, whereas regeneration kinetics became slower for cobalt complexes with less driving force for regeneration. A driving force for dye regeneration of 390 mV for cobalt(II/III) tris(5-chloro-1,10-phenanthroline) was found sufficient to regenerate more than 80% of the D35 dye molecules, resulting in a conversion of incident photons to electric current of above 80%. The photocurrent of the D35 sensitized DSCs using cobalt phenanthroline complexes decreased, however, with increasing Nernst potential of the redox couples, due to the increased recombination and the decreased regeneration rate constants.
The dye-sensitized solar cell (DSC) challenges conventional photovoltaics with its potential for low-cost production and its flexibility in terms of color and design. Transient absorption ...spectroscopy is widely used to unravel the working mechanism of DSCs. A surprising, unexplained feature observed in these studies is an apparent bleach of the ground-state absorption of the dye, under conditions where the dye is in the ground state. Here, we demonstrate that this feature can be attributed to a change of the local electric field affecting the absorption spectrum of the dye, an effect related to the Stark effect first reported in 1913. We present a method for measuring the effect of an externally applied electric field on the absorption of dye monolayers adsorbed on flat TiO2 substrates. The measured signal has the shape of the first derivative of the absorption spectra of the dyes and reverses sign along with the reversion of the direction of the change in dipole moment upon excitation relative to the TiO2 surface. A very similar signal is observed in photoinduced absorption spectra of dye-sensitized TiO2 electrodes under solar cell conditions, demonstrating that the electric field across the dye molecules changes upon illumination. This result has important implications for the analysis of transient absorption spectra of DSCs and other molecular optoelectronic devices and challenges the interpretation of many previously published results.
Context. High-contrast instruments like SPHERE (Spectro- Polarimetric High-contrast Exoplanet REsearch) enable spatial resolution of young planetary systems and allow us to study the connection ...between planets and the dust contained in debris discs by the gravitational influence a planet can have on its environment. Aims. We present new observations of the edge-on debris disc around HD 15115 (F star at 48.2 pc) obtained in the near-IR. We search for observational evidence for a second inner planetesimal ring in the system. Methods. We obtained total intensity and polarimetric data in the broad bands J and H and processed the data with differential imaging techniques achieving an angular resolution of about 40 mas. A grid of models describing the spatial distribution of the grains in the disc is generated to constrain the geometric parameters of the disc and to explore the presence of a second belt. We perform a photometric analysis of the data and compare disc brightness in two bands in scattered and in polarized light. Results. We observe an axisymmetric planetesimal belt with a radius of ~2′′, an inclination of 85.8° ± 0.7° and position angle of 278.9° ± 0.1°. The photometric analysis shows that the west side is ~2.5 times brighter in total intensity than the east side in both bands, while for polarized light in the J band this ratio is only 1.25. We also find that the J–H colour of the disc appears to be red for the radial separations r ≲ 2′′ and is getting bluer for the larger separations. The maximum polarization fraction is 15–20% at r ~ 2.5′′. The polarized intensity image shows some structural features inside the belt which can be interpreted as an additional inner belt. Conclusions. The apparent change of disc colour from red to blue with an increasing radial separation from the star could be explained by the decreasing average grain size with distance. The presence of an inner belt slightly inclined with respect to the main planetesimal belt is suspected from the data but the analysis and modelling presented here cannot establish a firm conclusion due to the faintness of the disc and its high inclination.
Linker unit modification of donor-linker-acceptor-based organic dyes was investigated with respect to the spectral and physicochemical properties of the dyes. The spectral response for a series of ...triphenylamine (TPA)-based organic dyes, called LEG1–4, was shifted into the red wavelength region, and the extinction coefficient of the dyes was increased by introducing different substituted dithiophene units on the π-conjugated linker. The photovoltaic performance of dye-sensitized solar cells (DSCs) incorporating the different dyes in combination with cobalt-based electrolytes was found to be dependent on dye binding. The binding morphology of the dyes on the TiO2 was studied using photoelectron spectroscopy, which demonstrated that the introduction of alkyl chains and different substituents on the dithiophene linker unit resulted in a larger tilt angle of the dyes with respect to the normal of the TiO2-surface, and thereby a lower surface coverage. The good photovoltaic performance for cobalt electrolyte-based DSCs found here and by other groups using TPA-based organic dyes with a cyclopentadithiophene linker unit substituted with alkyl chains was mainly attributed to the extended spectral response of the dye, whereas the larger tilt angle of the dye with respect to the TiO2-surface resulted in less efficient packing of the dye molecules and enhanced recombination between electrons in TiO2 and Co(III) species in the electrolyte.
Context.
In recent years, protoplanetary disks with spiral structures have been detected in scattered light, millimeter continuum, and CO gas emission. The mechanisms causing these structures are ...still under debate. A popular scenario to drive the spiral arms is the one of a planet perturbing the material in the disk. However, if the disk is massive, gravitational instability isusually the favored explanation. Multiwavelength studies could be helpful to distinguish between the two scenarios. So far, only a handful of disks with spiral arms have been observed in both scattered light and millimeter continuum.
Aims.
We aim to perform an in-depth characterization of the protoplanetary disk morphology around WaOph 6 analyzing data obtained at different wavelengths, as well as to investigate the origin of the spiral features in the disk.
Methods.
We present the first near-infrared polarimetric observations of WaOph 6 obtained with SPHERE at the VLT and compare them to archival millimeter continuum ALMA observations. We traced the spiral features in both data sets and estimated the respective pitch angles. We discuss the different scenarios that can give rise to the spiral arms in WaOph 6. We tested the planetary perturber hypothesis by performing hydrodynamical and radiative transfer simulations to compare them with scattered light and millimeter continuum observations.
Results.
We confirm that the spiral structure is present in our polarized scattered light
H
-band observationsof WaOph 6, making it the youngest disk with spiral arms detected at these wavelengths. From the comparison to the millimeter ALMA-DSHARP observations, we confirm that the disk is flared. We explore the possibility of a massive planetary perturber driving the spiral arms by running hydrodynamical and radiative transfer simulations, and we find that a planet of minimum 10
M
Jup
outside of the observed spiral structure is able to drive spiral arms that resemble the ones in the observations. We derive detection limits from our SPHERE observations and get estimates of the planet’s contrast from different evolutionary models.
Conclusions.
Up to now, no spiral arms had been observed in scattered light in disks around K and/or M stars with ages <1 Myr. Future observations of WaOph 6 could allow us to test theoretical predictions for planet evolutionary models, as well as give us more insightinto the mechanisms driving the spiral arms.
Context. Debris disks correspond to the final evolutionary stage of circumstellar disks around young stars. Gas-deprived structures seen in debris disks are normally, but not always, attributed to ...dynamical interactions in young planetary systems. Aims. The debris disk of HIP 73145 has been detected in scattered light in the near-IR, and at far-IR wavelengths before, but no substructure has been seen so far. Detection of such substructures in combination with detailed modeling can hint at the presence of perturbing planetary bodies, or reveal other mechanisms acting to replenish gas and dust reservoirs and forming structures such as spirals or rings. Methods. We obtained multiwavelength images with SPHERE in the near-IR in the H2 and H3 bands with the IRDIS camera and a 0.95−1.35 μm spectral cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. The SPHERE standard suite of angular differential imaging algorithms was applied. ALMA Band 6 observations complement the SPHERE data. Results. We detect a bright ring of scattered light plus some secondary structures inside, at least one of them forming a secondary, concentric ring with the first. This is the first detection of this disk in total-intensity scattered light. A second object is detected in the field at high contrast but concluded to be a background star. Forward modeling yields information on the primary parameters of the disk and confirms that the detected substructures are not due to the data analysis approach, which sometimes leads to spurious structures. Conclusions. We detect a series of concentric rings in the disk around HIP 73145. This is one of the rare cases where multiple components are necessary to fit the SED and are also detected in scattered light. The presence of such ring structures somewhat questions the nature of the object as a pure debris disk, but the gas and dust content would presumably offer sufficient explanations for such structures to form.
22q11.2 duplication syndrome has a frequency of ~1/700 in the intellectual disability population. Despite this frequency, there is limited information on the variable clinical presentation. Although ...the phenotype and incidence of congenital anomalies are well described for 22q11.2 deletion syndrome, they are not as well understood for individuals with 22q11.2 duplication syndrome. This study is a single-center, retrospective review of patients diagnosed with 22q11.2 duplication syndrome designed to categorize the variable phenotype seen in these individuals. The data suggest that the incidence of congenital anomalies may be higher than previously reported for this syndrome. Affected individuals are at increased risk for a variety of problems including gastrointestinal complications, endocrine dysfunction, ophthalmologic abnormalities, palatal anomalies, congenital heart disease, musculoskeletal differences, and neurologic abnormalities. Individuals with 22q11.2 duplication syndrome would benefit from care coordinated by a multidisciplinary team and managed according to the 22q11.2 deletion syndrome guidelines.
Context. The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter ...emission which are possibly related to planet formation processes. Aims. We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface. Methods. We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features. Results. The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the Uφ image of the J-band observation can be attributed to multiple scattering in the disk. Conclusions. The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. Possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. The spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.′′0.
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