Multilayered Solar Energy Converters with Flexible Sequence of p and n Semiconductor Films

Non-traditional design of multi-layered solar energy converters is proposed, with electrically independent p-i-n junctions. This new approach allows utilization of cheap and abundant II-VI, IV and IV-VI materials instead of III-V ones, using also cheap and economic deposition techniques like Chemical Bath Deposition (CBD) or Chemical Vapor Deposition (CVD) instead of expensive Molecular Beam Epitaxy (MBE). The CVD reactor with three atomic sources was built and used. II-VI and IV-VI semiconductor materials were prepared either in CVD reactor, or by CBD techniques. Besides, the original two-stage technology was employed: first the precursor oxide/hydroxide film of corresponding metal (like cadmium oxide/hydroxide) was prepared by some variety of CBD methods, and at the second stage, in CVD reactor the non-metallic component of precursor film was substituted by chalcogen, producing materials like CdS, CdSe, PbTe, etc. The semiconductor materials thus produced were of high quality, with basic parameters corresponding to those for the single crystals. Several experimental multilayered converters were constructed (in particular, with CdS/CdTe, CdS/PbS and Si/PbTe active bilayers). The preliminary results of their studying have shown that these and similar devices can be used in solar cells and photo sensors with satisfactory efficiency, and have great potential for improvement

Chemical abundance analysis of the Open Clusters Berkeley 32, NGC 752, Hyades and Praesepe

Context. Open clusters are ideal test particles to study the chemical evolution of the Galactic disc. However the existing high-resolution abundance determinations, not only of [Fe/H], but also of other key elements, is largely insufficient at the moment. Aims. To increase the number of Galactic open clusters with high quality abundance determinations, and to gather all the literature determinations published so far. Methods. Using high-resolution (R~30000), high-quality (S/N$>60 per pixel), we obtained spectra for twelve stars in four open clusters with the fiber spectrograph FOCES, at the 2.2 Calar Alto Telescope in Spain. We use the classical equivalent widths analysis to obtain accurate abundances of sixteen elements: Al, Ba, Ca, Co, Cr, Fe, La, Mg, Na, Nd, Ni, Sc, Si, Ti, V, Y. Oxygen abundances have been derived through spectral synthesis of the 6300 A forbidden line. Results. We provide the first determination of abundance ratios other than Fe for NGC 752 giants, and ratios in agreement with the literature for the Hyades, Praesepe and Be 32. We use a compilation of literature data to study Galactic trends of [Fe/H] and [alpha/Fe] with Galactocentric radius, age, and height above the Galactic plane. We find no significant trends, but some indication for a flattening of [Fe/H] at large Rgc, and for younger ages in the inner disc. We also found a possible decrease of [Fe/H] with |z| in the outer disc, and a weak increase of [alpha/Fe] with Rgc.Comment: 21 pages, Accepted for publication in A&A, Updated Table 1

Copper Incorporation into CdS Thin Films by Ionic Exchange in an Aqueous Solution Process at Room Temperature

Cadmium sulfide (CdS) thin films were deposited, on glass substrates, at 70°C for 120 min using an ammonium-free chemical bath deposition process. After deposition, the films were placed in a CuCl2 solution for 45, 60, 75, and 90 min, respectively, for their ion exchange, generating CdxCu1-xS films. The obtained films were analyzed by X-ray diffraction, Raman spectroscopy, X-ray wavelength dispersion spectrometry, and scanning electron microscopy. The reference CdS films showed a homogeneous appearance and a yellowish color; elapsing the immersion time, the films changed their color showing a greenish appearance. The X-ray analysis indicated that the CdS films developed a hexagonal structure with preferential orientation along the plane (002). During the ion exchange, a decrease in the intensity of the reflection (002) was observed as well as a slight displacement of this reflection towards higher values of 2θ derived from the substitution of Cd atoms by Cu atoms. The WDS analysis revealed that approximately 10% of the cadmium atoms were replaced by copper ones after 90 min of immersion

EFFECTS OF THE ANNEALING AND CdCl 2 TREATMENT ON THE STRUCTURAL AND OPTICAL PROPERTIES OF AMMONIA-FREE AND AMMONIA CdS THIN FILMS BY CHEMICAL BATH DEPOSITION

CdS thin films, with and without ammonia, were prepared using the chemical bath deposition method (CBD), with bath temperature of 70 0 C, 20 and 60 min times of reaction and different complexing agents. We study the effects of CdCl 2 treatment and annealing on these films. The thin films were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), optical absorption spectroscopy and Atomic Force Microscopy (AFM). The XRD measurements showed that the films have polycrystalline nature, hexagonal structure and the crystallites are oriented preferentially with the (002) and (110) planes. The optical absorption measurements show the presence of direct transition with energy band gaps of 2.55 eV and 2.44 eV and after diminished to 2.37 eV and 2.36 eV

Photocatalytic thin films containing TiO2:N nanopowders obtained by the layer-by-layer self-assembling method

Artículo de publicación ISIIn this work, TiO2–N powders were synthesized by high-energy ball milling, using commercial titanium dioxide (TiO2) in the anatase phase and urea to introduce nitrogen into TiO2 in order to enhance their photocatalytic properties in the visible spectral region. Several samples were prepared by milling a mixture of TiO2–urea during 2, 4, 8, 12 and 24 h and characterized by spectroscopic and analytical techniques. X-ray diffraction (XRD) results showed the coexistence of anatase and high-pressure srilankite TiO2 crystalline phases in the samples. Scanning electron microscopy (SEM) revealed that the grain size of the powder samples decreases to 200 nm at 24 h milling time. UV–Vis diffuse reflectance spectroscopic data showed a clear red-shift in the onset of light absorption from 387 to 469 nm as consequence of nitrogen doping in the samples. The photocatalytic activity of the TiO2–N samples was evaluated by methylene blue degradation under visible light irradiation. It was found that TiO2–N samples had higher photocatalytic activity than undoped TiO2 samples, which could be assigned to the effect of introducing N atoms and XPS results confirm it. Using polyethylenimine (PEI), transparent thin films of TiO2–N nanoparticles were prepared by layer-by-layer self assembly method. UV–visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO2 and PEI after each dip cycle. The adsorption of both TiO2 and PEI showed a saturation dip time of 15 min