Opal-like photonic structuring of perovskite solar cells using a genetic algorithm approach

Light management is an important area of photovoltaic research, but little is known about it in perovskite solar cells. The present work numerically studies the positive effect of structuring the photo-active layer of perovskite material. This structuration consists of a hybrid absorbing layer made of an uniform part and an opal-like part. A genetic algorithm approach allows us to determine the optimal combination among more than 1.4 10 potential combinations. The optimal combination provides an internal quantum efficiency of 98.1%, nearly 2% higher than for an equivalent unstructured photo-active layer. The robustness of the optimum against potential experimental deviations, as well as the angular dependency of the proposed structure, are examined in the present study.ELSSOL; ARC - Actions de Recherche Concerté

Tests of achromatic phase shifters performed on the SYNAPSE test bench: a progress report

The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation for future space missions (viz. Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA, Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial de Li\`ege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current work aiming at evaluating these prototypes on the SYNAPSE test bench at the Institut d'Astrophysique Spatiale in Orsay, France

Asgard/NOTT: L-band nulling interferometry at the VLTI I. Simulating the expected high-contrast performance

Context: NOTT (formerly Hi-5) is a new high-contrast L' band (3.5-4.0 \textmu m) beam combiner for the VLTI with the ambitious goal to be sensitive to young giant exoplanets down to 5 mas separation around nearby stars. The performance of nulling interferometers in these wavelengths is affected both by fundamental noise from the background and by the contributions of instrumental noises. This motivates the development of end-to-end simulations to optimize these instruments. Aims: To enable the performance evaluation and inform the design of such instruments on the current and future infrastructures, taking into account the different sources of noise, and their correlation. Methods: SCIFYsim is an end-to-end simulator for single mode filtered beam combiners, with an emphasis on nulling interferometers. It is used to compute a covariance matrix of the errors. Statistical detection tests based on likelihood ratios are then used to compute compound detection limits for the instrument. Results: With the current assumptions on the performance of the wavefront correction systems, the errors are dominated by correlated instrumental errors down to stars of magnitude 6-7 in the L band, beyond which thermal background from the telescopes and relay system becomes dominant. Conclusions: SCIFYsim is suited to anticipate some of the challenges of design, tuning, operation and signal processing for integrated optics beam combiners. The detection limits found for this early version of NOTT simulation with the unit telescopes are compatible with detections at contrasts up to $10^5$ in the L band at separations of 5 to 80 mas around bright stars

Asgard/NOTT: L-band nulling interferometry at the VLTI. II. Warm optical design and injection system

Asgard/NOTT (previously Hi-5) is a European Research Council (ERC)-funded project hosted at KU Leuven and a new visitor instrument for the Very Large Telescope Interferometer (VLTI). Its primary goal is to image the snow line region around young stars using nulling interferometry in the L-band (3.5 to 4.0)$\mu$m, where the contrast between exoplanets and their host stars is advantageous. The breakthrough is the use of a photonic beam combiner, which only recently allowed the required theoretical raw contrast of $10^{-3}$ in this spectral range. Nulling interferometry observations of exoplanets also require a high degree of balancing between the four pupils of the VLTI in terms of intensity, phase, and polarization. The injection into the beam combiner and the requirements of nulling interferometry are driving the design of the warm optics and the injection system. The optical design up to the beam combiner is presented. It offers a technical solution to efficiently couple the light from the VLTI into the beam combiner. During the coupling, the objective is to limit throughput losses to 5% of the best expected efficiency for the injection. To achieve this, a list of different loss sources is considered with their respective impact on the injection efficiency. Solutions are also proposed to meet the requirements on beam balancing for intensity, phase, and polarization. The different properties of the design are listed, including the optics used, their alignment and tolerances, and their impact on the instrumental performances in terms of throughput and null depth. The performance evaluation gives an expected throughput loss of less than <6.4% of the best efficiency for the injection and a null depth of $\sim2.10^{-3}$, mainly from optical path delay errors outside the scope of this work.Comment: Accepted for publication in JATIS. 23 pages, 11 figures, 8 table

Clinically Relevant Optical Properties of Bifocal, Trifocal, and Extended Depth of Focus Intraocular Lenses

PURPOSE: To experimentally compare the optical performance of three types of hydrophobic intraocular lenses (IOLs): extended depth of focus, bifocal, and trifocal. METHODS: The tested IOLs were: TECNIS ZMB00 (bifocal; Abbott Medical Optics, Abbott Park, IL), TECNIS Symfony ZXR00 (extended depth of focus; Abbott Medical Optics), and FineVision GFree hydrophobic (trifocal; PhysIOL, Liège, Belgium). Their surface topography was analyzed by optical microscopy. Modulation transfer function (MTF) and spherical aberrations were determined on optical bench for variable pupil apertures and with two cornea models (0 μm and +0.28 μm). United States Air Force target imaging was analyzed for different focal points (near, intermediate, and far). Point spread function (PSF) and halos were quantified and compared. RESULTS: The three lenses presented step-like optic topography. For a pupil size of 3 mm or greater, clearly distinctive MTF peaks were observed for all lenses: two peaks for the extended depth of focus and bifocal lenses with +1.75 and +4.00 diopters (D) addition, respectively, and three peaks for the trifocal lens with +1.75 and +3.50 addition for intermediate and near vision, respectively. The extended depth of focus and bifocal lens had slightly higher MTF at best focus with the +0.28 μm cornea model than with the 0 μm model, whereas the trifocal lens was likely to be more independent of the corneal spherical aberrations.CONCLUSIONS: It appears that the three lenses rely on light diffraction for their optical performance, presenting halos with comparable intensities. For small pupil apertures (< 3 mm), the MTF peaks for the far and intermediate focal distances of the trifocal and extended depth of focus lenses overlap, but the trifocal lens presented an additional MTF peak for the near focal points

Spectroscopy of the nonlinear refractive index of colloidal PbSe nanocrystals

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Spectroscopy of the nonlinear refractive index of PbSe nanocrystals

A spectroscopic study of the optical nonlinearities of PbSe colloidal solutions was performed with the Z-scan technique, at wavelengths between 1200 and 1750nm. No nonlinear absorption is observed, while the third order nonlinear refractive index n2 shows clear resonances, somewhat blueshifted relative to the exciton transitions in the absorbance spectrum. The occurence of thermal effects are ruled out by time-resolved measurements. At resonance, measured n2 values exceed typical bulk semiconductor values by two orders of magnitude. At high optical intensity, the refractive index change saturates, indicating that state-filling lies at the origin of the observed effect. PbSe nanocrystals exhibit a bandgap absorption tunable around 1310 and 1550nm, offering a great potential for the use of these particles on a Si platform. We present a spectroscopic study on the nonlinear refractive index of colloidal PbSe nanocrystal suspensions (Q-PbSe sols) using the Z-scan method. Monodisperse Q-PbSe sols with a bandgap absorption tunable between 1250 and 1900nm were prepared by a wet chemical synthesis. Particles of 3 different sizes have been studied (3.9,5.2 and 5.9nm, with respective absorbance peaks of 1245,1550 and 1700nm). The nonlinear refractive index n2 and absorption beta have been measured as a function of light intensity in the range of 1200-1350nm and 1550-1750nm, using an 82MHz femtosecond pulsed laser. Our results demonstrate that n2 exhibits a clear resonant behaviour, correlated with the single photon transitions of the nanocrystals. Maximal n2 values of ~10^(-11) cm2/W were obtained for 1textmuM solutions. We attribute these high values to the strong confinement in Q-PbSe. Time-resolved experiments on the largest Q-PbSe sols enabled us to exclude thermal effects. As the long exciton lifetime (~1textmus) causes a saturation of the first exciton in the Q-PbSe at the light intensities used in these experiments, we suggest that bi-excitons contribute to the large nonlinearities observed. Changing the concentration of the Q-PbSe sols allowed us to calculate the n2 of the Q-PbSe, an important value when comparing with different systems, eg. thin films.info:eu-repo/semantics/publishe

Inverse Opal Photonic Nanostructures for Enhanced Light Harvesting in CH3NH3PbI3 Perovskite Solar Cells

peer reviewedLight management strategies using photonic crystals have been proven to efficiently improve light harvesting and subsequently conversion efficiency of various optoelectronic devices. This study focuses on 3D inverse opal CH3NH3PbI3 photoanodes in perovskite solar cells from a combined numerical and experimental approach. Varying the pore size and the layer thickness in numerical simulations, we first determined theoretical optimum from a purely optical point of view. Corresponding 3D inverse opal photonic nanostructures were then fabricated through spin-coating protocols using polystyrene nanospheres of various diameters as hard templating sacrificial agents. It demonstrates how the photonic nanostructuration of the perovskite layer impacts both optical and electronic properties of experimental samples. Regarding the individual 3D inverse opal perovskite layers, an optimum of light absorption is reached for an ∼500 nm diameter pore photonic nanostructure, with a photonic absorption enhancement as high as 16.1% compared to an unstructured compact benchmark. However, in addition to electronic-related countereffects, local light absorption in the hole transporting material is observed in assembled solar cells, weakening the light management benefits of the perovskite layer nanostructuration to only ∼3% photonic enhancement

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