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One of the important challenges in the field of perovskite solar cells is to investigate the competitive mechanisms of humidity and oxygen which improve the efficiency of cells at moderate humidity and cause the degradation of perovskites at high levels of moisture. We found that when an un-encapsulated standard planar architecture, glass/ITO/SnO2/triple cation perovskite/Spiro-OMeTAD/Au, was realized, exposure to moderate humid air was always needed for proper functioning. We investigated the fabrication and storage procedures of thin (∼320 nm) triple cation perovskite solar cells showing, for the first time, to the best of our knowledge, a remarkable enhancement of all photovoltaic parameters compared to those of pristine cells (with the fill factor exceeding 80%, a short circuit current density of about 24 mA cm-2 and an open circuit voltage of 1121 mV, for champion devices) and, particularly, an impressive increase of power conversion efficiency (PCE) from 13.2% to 20.8% after 72 h of storage in air with moderate humidity. A slight PCE increase to 20.9% was also achieved after subsequent low vacuum storage and after 720 h from the fabrication day. Moreover, devices exhibiting hysteresis-free behavior after storage were characterized for evaluating the mechanism of charge carrier recombination by means of dark and light current density-voltage and illumination-dependent photovoltaic parameters. The storage cycle shown in this work could be a possible route to improve the performance of pristine perovskite solar cells and consequently to proceed with encapsulation procedures.

Perovskite/silicon tandem solar cells have strong potential for high efficiency and low cost photovoltaics. In monolithic (two-terminal) configurations, one key element is the interconnection region of the two subcells, which should be designed for optimal light management and prevention of parasitic p/n junctions. We investigated monolithic perovskite/silicon-heterojunction (SHJ) tandem solar cells with a p/n nanocrystalline silicon/silicon-oxide recombination junction for improved infrared light management. This design can additionally provide for resilience to shunts and simplified cell processing. We probed modified SHJ solar cells, made from double-side polished n-type Si wafers, which included the proposed front-side p/n tunnel junction with the p-type film simultaneously functioning as selective charge transport layer for the SHJ bottom cell, trying different thicknesses for the n-type layer. Full tandem devices were then tested, by applying a planar n-i-p mixed-cation mixed-halide perovskite top cell, fabricated via low temperature solution methods to be compatible with the processed Si wafer. We demonstrate the feasibility of this tandem cell configuration over a 1 cm2 area with negligible J-V hysteresis and a VOC ~1.8 V, matching the sum of the VOC-s contributed by the two components.

We experimentally demonstrate the excitation of Bloch surface waves on the tip of single-mode optical fibers via a grating-coupled mechanism. In spite of unavoidable fabrication-related tolerances, we evaluate sensing performances in line with state-of-the-art plasmonic benchmarks, paving the way for the development of advanced 'all-dielectric' lab-on-fiber optrodes. © 2018 IEEE.

Focused ion beam milling is used to nanopattern doped silicon oxide layer in view of light trapping application in thin film photovoltaics. Different working conditions, such as ion beam currents, milling times, dwell times, etc., are optimized in order to improve the nanochannel shape by reducing the effect of redeposition of sputtered target material on the sidewalls. This phenomenon, due to ion beam striking on the target layer, induces a V-shape instead of the desired box-shape for the nanochannels. A suitable milling strategy is here explored to reduce this effect. The results show that the parallel scan routine with "bottom to top" direction gives a more appropriate shape. Also parallel multi-pass milling and 3 � 1017 ions/cm2 ion dose result in reduced redeposition. Sputtering yield is calculated both experimentally and theoretically, and correlated with the redeposition. Due to the focused ion beam peculiarity, nanopatterning can be achieved, without utilizing an etching mask or resist layer, which is advantageous for fabrication of prototype devices. � 2013 Elsevier Ltd. All rights reserved.

Soft self-assembling photonic materials such as cholesteric liquid crystals are attractive due to their multiple unique and useful properties, in particular, an optical band gap that can be continuously and dynamically tuned in response to weak external influences, easy device integration, compatibility with flexible architectures, and, as shown here, potential for submicrometer optical applications. We study such a system formed by a short-pitch cholesteric confined in the core of polymer fibers produced by coaxial electrospinning, showing that the selective reflection arising from the helical photonic structure of the liquid crystal is present even when its confining cavity is well below a micrometer in thickness, allowing as little as just half a turn of the helix to develop. At this scale, small height variations result in a dramatic change in the reflected color, in striking difference to the bulk behavior. These conclusions are made possible by combining focused ion beam (FIB) dissection and imaging of the internal fiber morphology with optical microscopy. The FIB dissection further reveals that the cross section of the cavity within the fiber can have a shape that is quite different from that of the outside fiber. This is critical for the photonic behavior of the composite fiber because different optical textures are generated not only by change in thickness but also by the shape of the cavity. Our results provide insights into the behavior of cholesterics in submicrometer cavities and demonstrate their potential at such dimensions. © 2013 American Chemical Society.

We report on the first example of a "meta-tip" configuration that integrates a metasurface on the tip of an optical fiber. Our proposed design is based on an inverted-Babinet plasmonic metasurface obtained by patterning (via focused ion beam) a thin gold film deposited on the tip of an optical fiber, so as to realize an array of rectangular aperture nanoantennas with spatially modulated sizes. By properly tuning the resonances of the aperture nanoantennas, abrupt variations can be impressed in the field wavefront and polarization. We fabricated and characterized several proof-of-principle prototypes operating an near-infrared wavelengths, and implementing the beam-steering (with various angles) of the cross-polarized component, as well as the excitation of surface waves. Our results pave the way to the integration of the exceptional field-manipulation capabilities enabled by metasurfaces with the versatility and ubiquity of fiber-optics technological platforms. © 2016 SPIE.

In this paper, nanoscale organic two-terminal devices, based on evaporated films of a perylene diimide derivative (PDI8-CN2) and with channel lengths ranging from 1 μm down to 50 nm, have been fabricated by using Focused Ion Beam technique. Devices have been characterized in terms of I–V curves at several temperatures and perylene diimide nanochannels displayed a measurable electrical conduction even at temperatures lower than 50 K. The recorded experimental data stressed the electrical response according to the channel size. Investigation of nanoscale devices allowed us to study the nature of the charge injection and to estimate the energy barrier and the factors influencing it.

We realize the first optical-fiber "meta-tip" that integrates a metasurface on the tip of an optical fiber. In our proposed configuration a Babinet-inverted plasmonic metasurface is fabricated by patterning (via focused-ion-beam) an array of rectangular aperture nanoantennas in a thin gold film. Via spatial modulation of the nanoantennas size, we properly tune their resonances so as to impress abrupt arbitrary phase variations in the transmitted field wavefront. As a proof-of-principle, we fabricate and characterize several prototypes implementing in the near-infrared the beam-steering with various angles. We also explore the limit case where surface waves are excited, and its capability to work as refractive index sensors. Notably, its sensitivity overwhelms that of the corresponding gradient-free plasmonic array, thus paving the way to the use of metasurfaces for label-free chemical and biological sensing. Our experimental results, in fairly good agreement with numerical predictions, demonstrate the practical feasibility of the meta-tip concept, and set the stage for the integration of metasurfaces, and their exceptional capabilities to manipulate light, in fiber-optics technological platforms, within the emerging "lab-on-fiber" paradigm. © 2016 SPIE.

We report on a method for integrating sub-wavelength resonant structures on top of optical fiber tip. Our fabrication technique is based on direct milling of the glass on the fiber facet by means of focused ion beam. The patterned fiber tip acts as a structured template for successive depositions of any responsive or functional overlay. The proposed method is validated by depositing on the patterned fiber a high refractive index material layer, to obtain a ‘double-layer’ photonic crystal slab supporting guided resonances, appearing as peaks in the reflection spectrum. Morphological and optical characterizations are performed to investigate the effects of the fabrication process. Our results show how undesired effects, intrinsic to the fabrication procedure should be taken into account in order to guarantee a successful development of the device. Moreover, to demonstrate the flexibility of our approach and the possibility to engineering the resonances, a thin layer of gold is also deposited on the fiber tip, giving rise to a hybrid photonic-plasmonic structure with a complementary spectral response and different optical field distribution at the resonant wavelengths. Overall, this work represents a significant step forward the consolidation of Lab-on-Fiber Technology.

Surface texturing plays an important role to reduce light reflection and improve light confinement within silicon substrate thus resulting in solar cell efficiency enhancement. In this paper wet anisotropic texturing and subsequent wet isotropic smoothing of different thickness c-Si wafers are investigated to light trapping improvement. The influence of reagent concentration and etching time of the process smoothing are studied. The reflection properties of textured wafers, before and after smoothing steps, are monitored using UV-VIS spectrophotometer and the surface morphology images are acquired by scanning electron microscope. © 2014 AEIT.

We have visualized the internal structure of electrospun polymer fibers, having liquid crystals in the core, using focused ion beam milling. In this way we were able to correlate observed selective reflection and optical texture, in a specific fiber location, with the corresponding cavity dimensions and shape. It was found that cholesteric liquid crystals exhibit peculiar optical behavior, distinctively different from the one in bulk, when they are confined in sub-micrometer cavities. Because of the reduced dimensions, the pitch of the helix has to change even for tiny variations in cavity size, resulting in changes in the wavelength of the selective reflection. The ion beam milling is a destructive process and it is relevant to consider possible side effects and consequences on the polymer sheath and thus on the revealed cavities. We analyze the heating due to the ion beam exposure calculating the subsequent temperature increase in the polymer and at a polymer-liquid crystal interface. The derived increase of temperature is very small and is not expected to induce any notable change in the polymer cavities. © 2014 SPIE.

Recently, great efforts have been carried out to design optimized metallic nano-grating back-reflectors to improve the light absorption in thin film solar cells. In this paper, is introduced a feasibility study on the prototyping of patterned substrate for solar cell fabrication. In particular, is demonstrated that the Focused Ion Beam lithography not affect the electric performances of the realized cell, giving us the opportunity to use this lithography technique for prototyping each kind of substrate for solar cell fabrication. © 2014 IEEE.

In this work we report the possibility to obtain a high refractive index grid anode directly on the substrate surface by fabricating a relatively large-area photonic crystal (PC) structure using the combinations of electron beam lithography (EBL) and focused ion beam (FIB) techniques. The performance of the realized photonic crystal (PC) structure were enhanced by milling the ITO layer until the glass substrate and by removing the further refractive index jump between the PC and the substrate. The good properties of highly conductive poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), ensured a continuous path for the current and a high refractive index jump for the PC structure by filling the holes in the PC structure.

In this paper we present an innovative diode based on the heterojunction between amorphous silicon and porous silicon grown on crystalline silicon. The device architecture gives several advantages. Deposition of amorphous silicon on porous material realises high performance junction at temperature less than 250°C and it passives the porous layer against the natural oxidation due to ageing in the environment. Porous technology allows to obtain a controlled textured silicon surface independently from crystalline silicon orientation just to give the opportunity to reduce surface reflectivity and the blue shift of the absorption spectra in solar cell application. Solar cells were characterised by I-V dark/light and quantum yield measurements. Under standard AM 1.5 light we obtained photovoltaic conversion efficiency greater than 10%. Change in photoluminescence in different gas environments showed for gas sensor applications give rise encouraging results. In dark condition we found the typical diode behaviour.