1,720,970 research outputs found
Textured p-type crystalline silicon surfaces obtained by multi-step plasma process for SHJ solar cells
No full textP-type monocrystalline silicon wafers were textured by means of a multi-step plasma etching technique with the aim of greatly reducing their reflectance and effectively exploiting the highest possible amount of solar radiation in heterojunction photovoltaic devices. Suitable surface morphologies, characterized by high light scattering, have to be obtained without damaging the c-Si electrical properties. For this reason, some aspects of the plasma etching process have been studied and improved. Modifications have been made to obtain both “cleaner” processes and energetically lower ion bombardment. By operating at high pressure (0.4 mbar), a process controlled by diffusion of reactive species towards the substrate was favoured. Another innovative aspect consisted in two “reconditioning” plasma processes of the Si surface before the actual silicon removal step with SF6 /O2 gas mixtures. A strong reduction in the average optical reflection down to 5% was obtained coupled with a minority carriers lifetime (τeff) of about 950 μs, value comparable to that of the untreated silicon. An interesting surface morphology, consisting in “U" shaped cavities, was obtained. Texture irregularities were easily removed by acid etching. The moderate depth of the cavities is very promising for an effective passivation with a-Si:H thin films
Microstructure evolution of room-temperature-sputtered ITO films suitable for silicon heterojunction solar cells
No full textThickness influence on structural, optical and electrical properties of sputtered indium tin oxide (ITO) with thickness ranging from 60 up to 430 nm films has been studied. At the increase of the film thickness crystallinity degree and grain size increased, whereas tensile structural distortion as well as resistivity decreased. It was observed that a microstructure evolution takes place: the initial amorphous layer evolved in polycrystalline phase, with a grain–subgrain surface morphology. Carrier concentration increased at the increase of the film thickness and a general relationship between electrical characteristics and structural distortion has been found. In thinner films larger tensile distortion allowed to include larger amount of interstitial O and/or Sn atoms in the lattice. An appreciable impact of the thickness was also observed on electro-optical properties in terms of changes in energy gap, resistivity and optical absorption. Silicon heterojunction solar cells have been produced and Jsc as high as 33.0 mA/cm2 has been obtained
Amorphous hybrid TiO2 thin films: The role of organic ligands and UV irradiation
No full textThe development of a simple, economic and low-temperature synthesis procedure for titanium oxide thin films is an important challenge, due to their diffusion and to the limitations imposed by high temperature annealing. The knowledge on the properties of amorphous TiO2 films, as well as on the effect of their functionalization by organic compounds, is still inadequate. Here we describe a hydrolytic sol-gel procedure to prepare TiO2-based hybrid (inorganic-organic) thin films containing four different complexing agents in their structure (acetylacetone, dibenzoylmethane, citric acid and diethanolamine). The process variables were explored in order to attain stable sols and to tune the features of the amorphous films resulting by drying at 80 °C. Their structural, morphological, optical and electrical properties were studied by SEM, AFM, XRD, ellipsometry, FT-IR and UV–vis-NIR spectroscopy and resistivity measurements. The effect of the organic component, precursors concentration, deposition parameters and annealing temperature was considered. Moreover, the modifications induced by the exposure of the hybrid films to UV light were deeply investigated. A short UV treatment has a strong impact on the microstructure and wettability of the films and promotes a striking increase in their electrical conductivity
Air-stable low-emissive AlN-Ag based coatings for energy-efficient retrofitting of existing windows
No full textLow-emissive (low-E) coatings, based on alternating thin layers of aluminium nitride (AlN) and ultra-thin layers of silver (Ag), have been deposited by sputtering for use on glass surface outside the inert gas filled gap of insulating multiple-pane windows. Such low-E coatings being optical filters containing thin metallic layers, undergo degradation phenomena when exposed to air with the appearance of a bluish colour and delamination. An in-depth study has been conducted to identify the degradation mechanism in moist atmosphere by means of several characterization techniques before and after accelerated aging tests. Photoluminescence measurements have evidenced formation of the complex defect VAl-3ON at the AlN/Ag interfaces as responsible for the hydrolytic degradation process. Relationship between degradation process and chemical-physical nature of AlN lattice defects has been established. Modifications in the sputtering process of AlN films were implemented and the antireflective layer was replaced with less hydrophilic material. The coating deposited with modified structure has been found to be highly stable and with excellent thermo-optical performances (SHGC 0.54, visible transmittance 80%, emissivity 4.8%). The modified low-E coatings have been also deposited on polycarbonate substrate with similar results of high stability in the air. This stabilized coating on polymer can be considered an excellent candidate for low-cost energy-saving retrofitting
Hydrogen-doped In2O3 for silicon heterojunction solar cells: Identification of a critical threshold for water content and rf sputtering power
No full textHydrogen-doped indium oxide (IO:H) layers with very high carrier mobility have been developed by two-step fabrication procedure. In the first step IO:H films were deposited by radio frequency (RF) magnetron sputtering from In2O3 target in Ar/water vapour gas mixtures. Different sputtering powers and partial pressures of H2O (pH2O) have been explored and effects induced by changes of these process parameters on final film structure and on electro-optical properties have been investigated. In the second step a post-deposition annealing under vacuum were performed. During this treatment a complete and complex amorphous-crystalline transition occurred. Growth of large crystalline domains give rise to IO:H films with excellent carrier mobility values, up to 138 cm2/Vs. For each sputtering power used, the pH2O range has been identified which allows to obtain the highest carrier mobility value for IOH post-annealed films. Growth of large crystallites occurred in IO:H annealed films and, at this purpose, a selective chemical etching method has been developed to give better evidence for the polycrystalline grains. IO:H films appeared formed by fairly large crystalline domains with presence of sub-grains. Silicon heterojunction cells fabricated by using IO:H layers as front electrode, compared with those obtained from a conventional ITO showed improved short-circuit current density and the resulting conversion efficiency
Determining the optical properties of Transparent and Conductive Oxides for thin film solar cells
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Sol-gel synthesis of ZnO transparent conductive films: The role of pH
No full textThe sol-gel synthesis of undoped and B- or Al-doped ZnO thin films were critically examined with particular reference to the influence of the pH of the reaction medium on some of their specific characteristics, such as thickness, morphology, doping level and optical properties, in view of their application in the photovoltaic field. Using triethanolamine (TEA) as chelating agent, a range of basic pH from 7.66 to 8.76 was explored starting from a very concentrated zinc acetate dehydrate (ZAD) solution in ethanol, [Zn2+] = 1.0 M, and keeping the ZAD/TEA = 1. A more basic environment gives more porous films whose thickness and crystallinity are higher than those achieved at lower pH. It was found that the morphology, as well as the sheet resistance (Rs) of films, depends on both pH and doping. Increasing the pH the Rs decreases for both undoped and doped films. At a certain pH undoped films exhibit a granular microstructure and lower Rs than B- or Al-doped films which exhibit a finer texture, characterized by a lower porosity. Optical properties strongly depend on the pH as well. Increasing the pH, a noticeable blue shift effect was observed, that was attributed mainly to structural changes and to a lesser extent to the Burnstein-Moss effect. © 2014 Elsevier B.V
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