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Ramirez D.,University of Valparaiso | Gomez H.,Pontifical Catholic University of Valparaiso | Riveros G.,University of Valparaiso | Schrebler R.,Pontifical Catholic University of Valparaiso | And 2 more authors.
Journal of Physical Chemistry C | Year: 2010

The effect of Zn(II) concentration on the electrodeposition of zinc oxide on very thin anodic alumina membranes has been investigated. The aim was to establish the best experimental conditions to completely fill the pores to facilitate the further growth of nanorods projected outside the template surface. Zinc perchlorate and molecular oxygen were employed as precursors for zinc oxide formation. Considering local pH changes that take place at the interface, diagrams of species distribution vs pH were built to interpret the steps of zinc oxide formation as the pores are progressively filled. The process was followed, recording the corresponding j/t transients. With the progressive diminution of Zn(II) concentration, the transients evolved from a "metallic type" growth (i.e., similar to that found during the growth of bulk zinc oxide films) toward a stationary state, similar to that reported for the growth of zinc oxide nanorods by self-assemby from solutions with low Zn(II) concentrations. SEM images showed that bundles of zinc oxide nanorods were partially liberated from the template at the lower concentration employed, behavior attributed to a progressive dissolution of the very thin anodic alumina membrane. © 2010 American Chemical Society. Source

Ramirez D.,Pontifical Catholic University of Valparaiso | Gomez H.,Pontifical Catholic University of Valparaiso | Lincot D.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep
Electrochimica Acta | Year: 2010

In this paper we report the zinc oxide nanorods (ZnO NRs) growth by electrochemical deposition onto polycrystalline gold electrodes modified with assemblies of polystyrene sphere monolayers (PSSMs). Growth occurs through the interstitial spaces between the hexagonally close packed spheres. ZnO NRs nucleate in the region where three adjacent spheres leave a space, being able to grow and projected over the PSSMs. The nanorod surface density (NNR) shows a linear dependence with respect to a PS sphere diameter selected. XRD analysis shows these ZnO NRs are highly oriented along the (0 0 2) plane (c-axis). This open the possibility to have electronic devices with mechanically supported nanometric materials. © 2009 Elsevier Ltd. All rights reserved. Source

Le Bris A.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Le Bris A.,Saint - Gobain | Rodiere J.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Colin C.,CNRS Optic of Semiconductor nanoStructures Group | And 8 more authors.
IEEE Journal of Photovoltaics | Year: 2012

In operating hot carrier solar cells, a steady-state hot carrier distribution is established in the absorber in such a way that the excess kinetic energy of carriers can be collected. A high-carrier concentration is normally favorable to the formation of a nonequilibrium hot-carrier population. A small absorber thickness is thus expected to improve the efficiency of hot carrier solar cells, but no quantitative analysis of the impact of the cell thickness on its performance has been done so far. Here, the potential of efficiency improvement using thinned absorber is investigated by simulating the absorption, heat losses, and efficiency of a hot carrier solar cell with varying absorber thickness. Efficiency improvement requires efficient light trapping to maintain absorption in ultrathin layers. Solutions are proposed to achieve strong absorption in a 25-50-nm-thick absorber, resulting in cell efficiencies that are higher than the Shockley-Queisser limit corresponding to the absorbers bandgap. © 2012 IEEE. Source

Erfurth F.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Jehl Z.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Bouttemy M.,University of Versailles | Dahan N.,Ecole Polytechnique - Palaiseau | And 9 more authors.
Applied Surface Science | Year: 2012

Chemical and optical properties of the interface between a coevaporated Cu(In,Ga)Se 2 (CIGSe) absorber thin film and the Mo back contact are investigated with the objective to reduce markedly the thickness of CIGSe layers from two microns down to about 100 nm. First a mechanical lift off technique allowed to separate Mo and CIGSe layers and perform X-ray photoelectron spectroscopy (XPS) and elipsometry studies on as prepared surfaces. On the Mo side small amounts of In and Ga are observed together with the formation of an MoSe 2 layer. There is no evidence of the presence of Cu. On the opposite CIGSe side a clear depletion of Cu together with an enrichment of Ga is evidenced. There is no evidence of Mo. Optical reflectivity of the interface CIGSe/Mo is studied by ellipsometry showing a low reflectivity of the interface attributed to the formation of MoSe 2 layer. The enhance light absorption in ultrathin absorbers using alternative, highly reflective back contacts are finally discussed. © 2011 Elsevier B.V. All rights reserved. Source

Mammadov E.,Azerbaijan Academy of Sciences | Naghavi N.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Jehl Z.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | Renou G.,Institute Of Recherche Et Developpement Sur Lenergie Photovoltaique Irdep | And 4 more authors.
Thin Solid Films | Year: 2014

Complex dielectric function of very thin ZnO films prepared with different oxygen concentration during deposition has been studied in 220-1700 nm and 2-25 μm spectral range. Variation of oxygen concentration in deposition chamber is intended to stabilize film properties by compensating oxygen deficiency. The films obtained by magnetron sputtering with thicknesses below 100 nm and optical axis perpendicular to sample surface were measured in standard ellipsometry configurations using rotating compensator ellipsometers. Dielectric function of the films obtained by fitting the experimental data using oscillator model exhibits narrowing and band edge oscillator center energy shifts from 3.178 to 3.355 eV for samples prepared with 0.5% and 1-2% oxygen, respectively. Results suggest ∼ 2% as the optimal oxygen concentration for preparation of optically stable films. Infrared dielectric function of the film prepared with 2% oxygen is also obtained. © 2014 Elsevier B.V. All rights reserved. Source

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