C. Fernández-Lorenzo - Academia.edu (original) (raw)

Papers by C. Fernández-Lorenzo

ABSTRACT TiO2 doping has been widely used in photocatalyis and photovoltaic cells to improve the ... more ABSTRACT TiO2 doping has been widely used in photocatalyis and photovoltaic cells to improve the performance of this semiconductor. This paper studies the use of copper as a dopant in TiO2 in Dye Sensitized Solar Cells (DSSC), analysing the effect on the photovoltaic properties of the cells of different concentrations of copper incorporated into the semiconductor. The Cu-doped TiO2 semiconductor was characterized with several instrumental techniques, including X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and UV-Vis spectroscopy in order to know its structure, composition and band gap energies with different concentrations of the dopant. An analysis was also performed of the variations in open-circuit voltage depending on the concentration of copper. This showed that the presence of copper in DSSCs made with a standard configuration - using a ruthenium complex (N3) as a dye and the redox pair I-/I3- as the electrolyte with 3-methoxypropionitrile as a solvent - leads to improvements of up to 10% in the open-circuit voltage of DSSCs.

One of the major limitations of the high resolution optical microscopy is the low depth of field.... more One of the major limitations of the high resolution optical microscopy is the low depth of field. This limitation is caused by the radiation used as illumination, and it depends on the wavelength of the radiation. However, the use of combined techniques of digital image acquisition and powerful software can afford to get completely focused images. The images obtained with this technique can show a virtual depth of field increased by an order of magnitude. In this chapter, we will show the way for obtaining extended depth of field images using a complete system (instrumentation, algorithm and software) for acquiring micrograph images and with no alteration of the original chromaticity. The dependence of the final result is shown according to the chromatic components used as the variables on the algorithm designed, so we will show a methodology based on the study of second variance in relation to the number of images and pixels of the chromatic coordinates to decide which to use as the basis for the calculation.

Transport in Porous Media, 2010

physica status solidi (c), 2004

An alternative method for stress relaxation in the SiC/Si heteroepitaxial system based on the inc... more An alternative method for stress relaxation in the SiC/Si heteroepitaxial system based on the incorporation of a group-IV element (germanium) into the interface between SiC and Si is presented. We have investigated the effect of the temperature during the predeposition of 1 ML of Ge on a silicon (111) surface, prior to the MBE carbonization. The resulting structures were investigated

Chemical Physics Letters, 2013

Journal of Sol-Gel Science and Technology, 1994

SiO2 gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extr... more SiO2 gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extremely fine dispersions of CdS semiconductor particles. Small crystallites were produced "in situ" by H2S gas diffusion method. The particles were characterized by TEM and HRTEM, EXAFS, UV-Vis and Raman spectroscopies. The size of crystallites ranged from 5 to 10 nm. The optical transmission spectra showed the characteristic blue shift as a function of the particles size, as predicted by the theory. The optical and mechanical qualities of the samples were substantially improved by an infiltration method using a sono-sol which sealed the superficial pores thus ensuring greater longevity and the possibility of obtaining transparent gels by polishing.

Journal of Nanofluids, Dec 1, 2018

This work presents a methodology and instrumental device for obtaining high resolution LBIC maps ... more This work presents a methodology and instrumental device for obtaining high resolution LBIC maps in conditions approximating to solar irradiation. The methodology developed is based on a system of trichromatic irradiation of the device under study. This irradiation system is composed of three lasers which emit in the red, green and blue regions of the solar spectrum. The methodology establishes the relative irradiation powers using the emission distribution of Planck's blackbody, which provides an approximation to solar emissions, and thus, the system establishes an initial approximation for obtaining high resolution LBIC scans under these conditions. The methodology includes an algorithm and a procedure capable of forming images from the three scans carried out with the three lasers, providing information about the quantum efficiency of the photovoltaic devices under solar irradiation conditions. To check the proposed methodology, LBIC scans are shown which were performed on a polycrystalline silicon solar cell. Furthermore, the study shows the variability of the device's photoelectric properties, which depend on the wavelength in the vicinity of grain boundaries.

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El objetivo fundamental de este trabajo es el estudio de la elaboracion de geles mixtos sio2 - p2... more El objetivo fundamental de este trabajo es el estudio de la elaboracion de geles mixtos sio2 - p2o5 y de su proceso de densificacion. Este estudio surge como paso previo a realizar para la sintesis de materiales avanzados de esta composiciones. La memoria esta dividida en tres partes. En la primera se realiza una descripcion de las diferentes etapas que constituyen la via sol-gel para la obtencion de materiales vitreos, incluyendo las rutas alternativas propuestas en los ultimos anos, asi como una breve exposicion de los fundamentos principales en los que apoyan las tecnicas utilizadas: espectroscopia raman y la resonancia magnetica nuclear. La segunda parte tiene como objetivo el estudio de la cinetica de obtencion de los geles mixtos sio2-p2o5. En ella se describe la obtencion de las muestras y la influencia de los reactivos utilizados en la elaboracion del gel asi como del metodo de preparacion. Por ultimo, la tercera parte se dedica a la obtencion de los aerogeles y al estudio d...

Science of Advanced Materials, 2014

ABSTRACT Highly aluminium-doped TiO2 nanoparticles were synthesized using a sol–gel method. The s... more ABSTRACT Highly aluminium-doped TiO2 nanoparticles were synthesized using a sol–gel method. The synthesized nanoparticles were annealed at different temperatures and their properties were characterized using ICP-AES, XRD, Raman spectroscopy, FT-IR, XPS, and UV-Vis to determine their composition, crystalline structure, band gap energy and possible use as semiconductors in photocatalytic and photovoltaic applications. The results revealed high internal doping due to the substitution of Ti4+ ions by Al3+ in the TiO2 lattice. The transformation from anatase to rutile phase occurred at higher temperatures when doping was increased. Furthermore, Raman, FT-IR and XPS showed the formation of oxygen vacancies to conserve the local charge neutrality in the TiO2 lattice. Thus, applying the synthesized material in photovoltaic and photocatalytic applications could be of interest. A photocatalytic application was developed based on the photodegradation of methylene blue. The aluminium doped samples synthesized in this study showed higher photocatalytic activity than the undoped ones.

Revista De Metalurgia, 2004

Progress in Photovoltaics: Research and Applications, 2004

ABSTRACT This paper presents the design of versatile equipment for obtaining laser-beam-induced c... more ABSTRACT This paper presents the design of versatile equipment for obtaining laser-beam-induced current (LBIC) images which allows the study of large surfaces as well as conversion areas of a few micrometers. The modular optomechanical design enables the user to modify the size of the irradiation spot by simply changing the microscope objective used as focal lens, albeit within the limits set by the wavelength. The use of an appropriate calculation algorithm makes it possible to rely on a computerized system to adjust the distance at which the focusing lens must be placed with respect to the sample plane. The possibility of working at micrometer resolution allows one to obtain very significant information for the study of irregularities, manufacturing defects, impurities, grain boundaries, dislocations, recombination centers, etc. in photovoltaic wafers. Copyright © 2004 John Wiley & Sons, Ltd.

physica status solidi (a), 2012

Molecular Physics, 2014

ABSTRACT We report a theoretical study of a series of Ru complexes of interest in dye-sensitised ... more ABSTRACT We report a theoretical study of a series of Ru complexes of interest in dye-sensitised solar cells, in organic light-emitting diodes, and in the war against cancer. Other metal centres, such as Cr, Co, Ni, Rh, Pd, and Pt, have been included for comparison purposes. The metal–ligand trends in organometallic chemistry for those compounds are shown synergistically by using three molecular descriptors: quantum theory of atoms in molecules (QTAIM), electron localisation function (ELF) and second-order perturbation theory analysis of the natural bond orbital (NBO). The metal–ligand bond order is addressed through both delocalisation index (DI) of QTAIM and fluctuation index (λ) of ELF. Correlation between DI and λ for Ru–N bond in those complexes is introduced for the first time. Electron transfer and stability was also assessed by the second-order perturbation theory analysis of the NBO. Electron transfer from the lone pair NBO of the ligands toward the antibonding lone pair NBO of the metal plays a relevant role in stabilising the complexes, providing useful insights into understanding the effect of the ‘expanded ligand’ principle in supramolecular chemistry. Finally, absorption wavelengths associated to the metal-to-ligand charge transfer transitions and the highest occupied molecular orbital (HOMO)--lowest unoccupied molecular orbital (LUMO) characteristics were studied by time-dependent density functional theory.

Journal of Crystal Growth, 2012

ABSTRACT Fabrication of high quality diamond either for gemmological or for technological applica... more ABSTRACT Fabrication of high quality diamond either for gemmological or for technological applications, is still a challenge. The control of impurity incorporation for doping or to modify the crystal colour should be still improved. The present contribution reports availability of nearly defect free HPHT (high pressure high temperature) diamond in terms of dislocations and point defects. Cathodoluminescence (CL) transitions related to point defects or dislocations (A-band) are not observed and only some individual dislocations are revealed by X-ray topography (topo-X). CL spectra are dominated by the excitonic-related transistions and the boron incorporation, estimated from the phonon-replica relative intensities, is around 1016 cm−3 that corroborate the values estimated by FTIR. Such amount of B gives a pale blue colour to the diamond sintetized monocrystal. The latter crystals are grown at the Instituto de Monocristales S.L. for jewellery applications, but their use for semiconducting applications is also envisaged after the highlights of the present study.

Diamond and Related Materials, 2010

A homoepitaxial boron-doped diamond single layer is investigated by means of Fourier transformed ... more A homoepitaxial boron-doped diamond single layer is investigated by means of Fourier transformed infrared spectroscopy (FTIR) and cathodoluminescence (CL). Both techniques are shown to be complementary. µ-FTIR mapping allows to determine the location of active boron while CL allows discernability between passivation and compensation. Hydrogen incorporation during chemical vapour deposition (CVD) growth is revealed to passivate boron acceptors. The obtained results highlight that plasma etching can induce a dissociation of B-H centres.