Paola Delli Veneri

Silicon oxide based n-doped layer for improved performance of thin film silicon solar cells

We propose the use of n-doped silicon oxide as alternative n-layer in thin film Si p-i-n solar cells. By varying input gas ratios, films with a wide range of optical and electrical properties are obtained. Applying these layers in solar cells, good electrical and optical properties are demonstrated. A relative efficiency increase up to 13.6% has been observed on the cells adopting a simple Ag back contact. A similar spectral response as with the cell with standard n-layer plus ZnO/Ag back contact is obtained. The deposition of a buffer layer at the back contact can therefore be avoided.

First and second-order Raman scattering in Si nanostructures within silicon nitride

First and second-order Raman analysis on annealed silicon nitride films is reported. Possible formation of amorphous Si nanoparticles after an intermediate treatment is deduced from the occurrence of a resonant spectrum. After nucleation of Si nanocrystals, with a model description of the first-order spectra it is possible to access information regarding mean radius, size dispersion, and crystalline phase fraction consistent with the fundamental data derived from microscopy. Substantial increase in second to first order intensity ratio is also observed: Enhanced electron–phonon coupling in both amorphous and crystalline Si nanoparticles is suggested.

Photoluminescence properties of partially phase separated silicon nitride films

Photoluminescence properties of partially phase separated amorphous silicon nitride films, lying in between homogeneous materials and composites embedding pure Si nanoparticles, have been investigated. With excitation energy above the Tauc gap, the emission band systematically blue-shifts and broadens with decreasing silicon content, suggesting tail to tail recombination as the prevailing luminescence mechanism. With subgap excitation, the response is instead peaked at 1.7 eV independently of the stoichiometry, likely as an effect of the spatial fluctuations of the gap. In this case, excitation and emission selectively occur in the Si rich domains within the material, and direct band to band recombination is proposed as the possible dominant process. Another effect of the nonuniform material composition is likely the unusual S-shaped evolution of the integrated photoluminescence intensity versus temperature observed for the sample richest in Si. This behavior has been described with a phenomenological mod...

Plasmonic Light Trapping in Thin-Film Solar Cells: Impact of Modeling on Performance Prediction

We present a comparative study on numerical models used to predict the absorption enhancement in thin-film solar cells due to the presence of structured back-reflectors exciting, at specific wavelengths, hybrid plasmonic-photonic resonances. To evaluate the effectiveness of the analyzed models, they have been applied in a case study: starting from a U-shaped textured glass thin-film, µc-Si:H solar cells have been successfully fabricated. The fabricated cells, with different intrinsic layer thicknesses, have been morphologically, optically and electrically characterized. The experimental results have been successively compared with the numerical predictions. We have found that, in contrast to basic models based on the underlying schematics of the cell, numerical models taking into account the real morphology of the fabricated device, are able to effectively predict the cells performances in terms of both optical absorption and short-circuit current values.

Doping of multilayer graphene for silicon based solar cells

In the present work we have tested the effects of graphene doping by nitrate ions and chlorine anions on graphene/n-silicon Schottky barrier solar cells, by the exposure to nitric acid and thionyl chloride vapors. In both cases the graphene doping process had beneficial effects on the power conversion efficiency (PCE) and thionyl chloride doping showed a better improvement than the one obtained with nitric acid. A solar cell with an initial PCE of 1.99% could be increased to 4.02% by nitric acid doping treatment while a solar cell with an initial PCE of 1.49% could be increased to 4.32% by thionyl chloride doping treatment.

Tinynose, an Auxiliary Smart Gas Sensor for RFID Tag in Vegetables Ripening Monitoring During Refrigerated Cargo Transport

Current state of the art’s real time monitoring of fresh produce, provides only temperature and humidity information. The idea is to develop new sensors and transport service assisted by ICT platform to monitor fresh produce quality. The technology will be based on radio frequency (RF) wireless network, and will provide real-time and in-site data-logging, enabling active management of food products in storage and transit. The RF sensor network design, allows an auxiliary sensor node to be “plugged in”. In this contribution we present the commercial platform developed starting from o fork of open hardware on which we assemble an array of commercial sensors in an “open air” configuration. We developed for this Embedded Gas Sensor System Device (Tinynose) two set-up: the “Development set-up” that uses a star wireless network infrastructure to store all raw sensor output and associated measurement error in a server DB to define parameters in ripening mathematical model and the “TAG set-up” that performs ripening evaluation in ICT in-site platform.

Vocs sensors based on polyaniline/graphene-nanosheets bilayer

In this work chemical sensors based on polyaniline and on polyaniline/graphene-nanosheets bilayer were prepared by dip coating. Their morphology and volatile organic compounds (VOCs) sensing behavior were compared. In particular, the devices were investigated in presence of VOCs as limonene and ethanol. Furthermore the devices were characterized under relative humidity. Bilayer samples, exposed to limonene, show a higher relative response respect to only polyaniline, encouraging the graphene use in VOCs sensor devices.

Amorphous/porous heterojunction on thin microcrystalline silicon

Abstract In this work we present a study of the fabrication of the junction between amorphous and porous silicon. Porous silicon was obtained by electrochemical etching of a 2 μm thick crystalline n-doped layer obtained by thermal recrystallisation of amorphous silicon deposited using chemical vapour deposition (CVD). A thin amorphous silicon emitter and an intrinsic buffer layer was deposited by plasma enhanced chemical vapour deposition (PECVD) to form the heterojunction. Photoluminescence (PL) measurements on porous film before and after heterojunction formation were performed and analysed with a model to determine the porous film properties. Current as a function of voltage was measured on the device which rectified for this kind of heterojunction.

MoOx as hole-selective collector in p-type Si heterojunction solar cells

We investigated the possible application of molybdenum oxide (MoOx) on the backside of p-type SHJ solar cells as substitute for the silicon-based back surface field layer. Solar cells with 4 cm2 area were fabricated on FZ c-Si(p) wafers, passivated with ultrathin i-a-Si:H buffers. A nanocrystalline n-SiOx emitter was applied while on the backside we applied 20 nm-thick p-type a-Si:H or evaporated MoOx (10 nm). Symmetric samples were additionally prepared to compare the effects on wafer passivation of MoOx versus the more conventional p-a-Si:H layer. For flat devices we have observed a Voc increase of ∼40 mV with MoOx replacing p-a-Si:H, with fill factors ∼73% in both the cases. Globally an efficiency increase of 1% absolute has been achieved moving to the MoOx hole collector. The feasibility of the MoOx/Ag backside configuration has been demonstrated also for textured p-type SHJ solar cells, reaching so far an efficiency of 18.1%.

Auxiliary smart gas sensor prototype plugged in a rfid active tag for ripening evaluation

Currently real time monitoring infrastructure of perishable goods, provides only temperature, humidity and CO2 information or different gas sensing devices are integrated as auxiliary sensors in RFID reader, but perhaps, nobody realizes a advanced gas sensor board with internal data elaboration able to extract the useful information for ripening evaluation. Starting from preliminary work in which first versions of infrastructure and devices have been developed to study algorithm and mathematical model, we have realized an innovative auxiliary smart sensor for freshness evaluation with the capability to be connected to an active RFID with power management policy. Final version of prototype is able to communicate with RF/ICT network of logistic platform and gives in real time, during transport, a quality indicator (ripening parameter) of the vegetable products by making a linear regression of differential measurements of temperature, humidity, VOC and ethylene level (olfactive footprint). Hardware and firmware design allows to easily modify gas sensor type, acquisition and conditioning parameters to adapt device to many olfactive scenarios. Laboratory tests have been performed simulating some of the typical failure conditions in a vegetable transport. Work in progress deals to optimize power consumption and mathematical model with onsite experimentation.