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8th World Conference on Photovoltaic Energy Conversion; 313-315, The aim of this work is the study of the degradation of two different PSCs. A PSC with undoped SnO2 ETL was compared to a PSC with ETL made of G-SnO2. Degradation was monitored by performing both impedance spectroscopy and dark I-V measurements. Experimental data were collected just immediately after fabrication and after one week. It was observed that the degradation of the solar cells affects both the AC behavior of the devices, modifying associated Nyquist plots, and the DC behavior, observable from dark current-voltage curves. From the Nyquist plots a quantitative analysis was performed by comparing the parameters of a proper equivalent circuit model. Results were coherent with those achieved with DC analysis, thus providing that the arising from these two techniques allows to gain a deeper knowledge of the degradation phenomena.

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.

The combination of responsive microgels and Lab-on-Fiber devices represents a valuable technological tool for developing advanced optrodes, especially useful for biomedical applications. Recently, we have reported on a fabrication method, based on the dip coating technique, for creating a microgels monolayer in a controlled fashion onto the fiber tip. In the wake of these results, with a view towards industrial applications, here we carefully analyze, by means of both morphological and optical characterizations, the effect of each fabrication step (fiber dipping, rinsing, and drying) on the microgels film properties. Interestingly, we demonstrate that it is possible to significantly reduce the duration (from 960 min to 31 min) and the complexity of the fabrication procedure, without compromising the quality of the microgels film at all. Repeatability studies are carried out to confirm the validity of the optimized deposition procedure. Moreover, the new procedure is successfully applied to different kinds of substrates (patterned gold and bare optical fiber glass), demonstrating the generality of our findings. Overall, the results presented in this work offer the possibility to improve of a factor ~30 the fabrication throughput of microgels-assisted optical fiber probes, thus enabling their possible exploitation in industrial applications. © 2018 by the authors.

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.

Vortex dynamics is strongly connected with the mechanisms responsible for the photon detection of superconducting devices. Indeed, the local suppression of superconductivity by photon absorption may trigger vortex nucleation and motion effects, which can make the superconducting state unstable. In addition, scaling down the thickness of the superconducting films and/or the width of the bridge geometry can strongly influence the transport properties of superconducting films, e.g. affecting its critical current as well as its switching current into the normal state. Understanding such instability can boost the performances of those superconducting devices based on nanowire geometries. We present an experimental study on the resistive switching in NbN and NbTiN ultra-thin films with a thickness of few nanometers. Despite both films were patterned with the same microbridge geometry, the two superconducting materials show different behaviors at very low applied magnetic fields. A comparison with other low temperature superconducting materials outlines the influence of geometry effects on the superconducting transport properties of these materials particularly useful for devices applications. © 2017 IEEE.

Integrating multi-responsive polymers such as microgels onto optical fiber tips, in a controlled fashion, enables unprecedented functionalities to Lab-on-fiber optrodes. The creation of a uniform microgel monolayer with a specific coverage factor is crucial for enhancing the probes responsivity to a pre-defined target parameter. Here we report a reliable fabrication strategy, based on the dip coating technique, for the controlled realization of microgel monolayer onto unconventional substrates, such as the optical fiber tip. The latter was previously covered by a plasmonic nanostructure to make it sensitive to superficial environment changes. Microgels have been prepared using specific Poly(N-isopropylacrylamide)-based monomers that enable bulky size changes in response to both temperature and pH variations. The formation of the microgel monolayer is efficiently controlled through the selection of suitable operating pH, temperature and concentration of particle dispersions used during the dipping procedure. The effect of each parameter has been evaluated, and the validity of our procedure is confirmed by means of both morphological and optical characterizations. We demonstrate that when the coverage factor exceeds 90%, the probe responsivity to microgels swelling/collapsing is significantly improved. Our study opens new paradigms for the development of engineered microgels assisted Lab-on-Fiber probes for biochemical applications. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

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.

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.

CH3NH3PbI3 layers have been prepared by two-step procedure (spin coating and dipping) on flat substrates under ambient conditions with uncontrolled relative humidity. The films have been characterized by means of scanning electron microscopy, absorption coefficient and x-ray diffraction when varying spinning rate, washing procedure, and dipping time. In particular a novel washing procedure has been developed to improve the film uniformity. The material has been tested as absorber layer in simplified solar cells by fabricating hole transport material free solar cells on flat substrates. The results demonstrate the possibility to realize planar solar cells even under uncontrolled conditions.

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.

ZnO nanorods are a good candidate for replacing standard photoanodes, such as TiO2, in perovskite solar cells and in principle superseding the high performances already obtained. This is possible because ZnO nanorods have a fast electron transport rate due to their large surface area. An array of ZnO nanorods is grown by chemical bath deposition starting from Al-doped ZnO (AZO) used both as a seed layer and as an efficient transparent anode in the visible spectral range. In particular, in this work we fabricate methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells using glass/AZO/ZnO nanorods/perovskite/Spiro-OMeTAD/Au as the architecture. The growth of ZnO nanorods has been optimized by varying the precursor concentrations, growth time and solution temperature. All the fabrication process and photovoltaic characterizations have been carried out in ambient air and the devices have not been encapsulated. Power conversion efficiency as high as 7.0% has been obtained with a good stability over 20 d. This is the highest reported value to the best of our knowledge and it is a promising result for the development of perovskite solar cells based on ZnO nanorods and AZO. © 2017 IOP Publishing Ltd.