1,721,049 research outputs found
Coupling of Bloch Surface Waves in amorphous silicon nitride multilayer structures: fundamentals and sensing applications
No full textMicrocrystalline silicon p-i-n photodetectors for telecommunications and photovoltaic applications
No full textCelle fotovoltaiche di alta efficienza a eterogiunzione silicio amorfo-nanocristallino/silicio cristallino per applicazioni industriali su vasta scala
No full textDal “PV Status report 2003” della Commissione Europea risulta che la produzione annua mondiale fotovoltaica presenta un incremento esponenziale a partire dal 1998. Estrapolando tale andamento le previsioni indicherebbero già per il 2010 una produzione annua mondiale di 8÷10 GWatt.
Un obbiettivo di tale portata potrà essere raggiunto solo se saranno disponibili processi di fabbricazione del dispositivo fotovoltaico, che rispondano ad una serie di requisiti fra i quali i principali sono:
- Alta efficienza di conversione (>20% AM1.5G)
- Processi a pochi stadi e a basso consumo di energia
- Lunga durata d'esercizio (>30 anni)
- Basso costo
- Abbondanza, reperibilità e non tossicità dei materiali usati
I dispositivi fotovoltaici ad eterogiunzione, oggetto della presente ricerca dal 1996, presentano le caratteristiche fisiche e tecnologiche in grado di rispondere, se adeguatamente sviluppate ai requisiti sopra elencati.
In particolare tali caratteristiche sono:
a) Possibilità di raggiungere alte efficienze di conversione (>20% AM1.5G) su dimensioni di interesse industriale, (10x10) cm2.
b) Processo di fabbricazione a bassa temperatura (≤ 200 °C) e basso consumo di energia.
c) Compatibilità del processo con wafer di silicio di grado solare, di basso costo, e di spessore sottile (≤ 200 mm).
d) Processo con un numero limitato di stadi con tempi complessivi di esecuzione relativamente bassi.
e) Trattandosi di silicio, è prevista una durata di esercizio, già sperimentata su dispositivi commerciali standard, prossima ai 30 anni.
In conclusione si ritiene che la presente attività di ricerca sul dispositivo fotovoltaico ad eterogiunzione possa ragionevolmente sfociare in applicazioni industriali nel breve-medio periodo
Synthesis and applications of nanostructured and nanocrystalline silicon based thin films
No full textIn the field of nanostructured materials, our research was focussed on the synthesis and applications of silicon based nanostructured films. In particular, we studied nanocrystalline Si and SiC thin films, having film thicknesses in the nanometer range and including nanometric grains, and compositionally modulated nanometric multilayers of a-Si3N4:H / a-SixN1-x:H. The Plasma Enhanced Chemical Vapor Deposition (PECVD) technique was used to deposit these materials at low temperature, which is advantageous for device applications. This paper is centred on our main results on p-type nanocrystalline Si (p nc-Si). The p nc-Si films were deposited by Very High Frequency (VHF) PECVD in high hydrogen dilution of the gas mixture at 170 °C. Our results on the application of these films in nanocrystalline Si / amorphous Si /crystalline Si heterojunction solar cells are discussed in details. The long range effects of plasma H atoms on the heterojunction nanostructure are studied by the simulation of optical spectra and the High Resolution Transmission Electron Microscopy (HRTEM) observations on the p nc-Si / i a-Si:H double layers deposited on c-Si substrates. The heterojunction built-in potential of these double layers is larger than in p a-Si:H / i a-Si:H structures and therefore in the nanocrystalline Si / amorphous Si /crystalline Si solar cell a Voc up to 640 mV can be obtained. The simulation of optical spectra and the HRTEM observations are reported and correlated with the corresponding solar cells characteristics
a-SiN:H Multilayer versus bulk structure: a real improvement of radiative efficiency?
No full textThe radiative properties of a-Si(0.6)N(0.4):Hla-Si(3)N(4):H multilayer structures are studied and compared to those of homogeneous a-Si(1-x)N(x):K films with x in the range 0.35-0.60. Transmission electron microscopy (TEM) shows interface abruptness in the multilayers. The photoluminescence (PL) efficiency of the multilayer structures is up to an order of magnitude larger than that of the him having the composition of the well layers. This result cannot be explained by an interface alloying model. The peak emission energy increase with decreasing well layer thickness is simulated in terms of spatial and quantum confinement models. The latter, associated with a disorder increase, gives the best fit
Electrical properties of silicon carbide/silicon rich carbide multilayers for photovoltaic applications
No full textSilicon carbide/silicon rich carbide multilayers, aimed at the formation of silicon nanodots for photovoltaic applications, have been studied. The electrical properties have been investigated at the nano-scale by conductive Atomic Force Microscopy (c-AFM) and at macro-scale by temperature dependent conductivity measurements. The mixture is composed of highly conductive Si nanoclusters and moderately conductive SiC nanoclusters in a disordered matrix. The conduction mechanism takes place via band states induced by the disorder at the interface between nanodot clusters. Structural properties have been extracted by optical spectroscopy analyses. The results contribute to the understanding of the microscopical electronic mechanisms of the composite material, which is a candidate for third generation photovoltaics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Electrical properties of silicon nanodots/Si rich carbide systems for photovoltaic applications
No full textSilicon nano-crystals (Si NCs) embedded in dielectric matrix are presently studied in view of their applications as tunable band-gap absorbers in all-silicon multi-junction photovoltaic cells.
SiC/SiC:Si multilayers produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) have been annealed to obtain Si NCs formation. Various experimental conditions (Si NCs size, doping level, crystallinity) have been considered.
Macroscopical as well as microscopical electrical characterizations were carried out in order to understand the conduction mechanisms. Conductivity measurements as a function of temperature showed that the conductivity ranged from 10-6-10-3 S/cm and the activation energy range is 0.19-0.4 eV.
Conductive-AFM was performed to identify the conductive path at nano-crystals level. The Si NCs showed enhanced conductivity with respect to the surrounding matrix. The measurements were correlated with optically determined crystallized fraction and with thermally activated transport properties
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
