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Item type:Publication, Fabrication and luminescence properties in Yb–Tb co-doped a-SiCO thin films(VBRI Press, 2020-07-24)Amorphous silicon oxycarbide (a-SiCxOy) single doped with Yb3+ and co-doped with the couple Tb3+ - Yb3+ thin films were grown on crystalline silicon substrates by rf magnetron sputtering. The elemental composition in at. % is determined by energy dispersive spectroscopy and fourier transform infrared spectroscopy allows to investigate the chemical properties of the host. The concentration of Yb in the single doped sample was 3.5% and for the codoped samples (Yb, Tb) were (3%, 0.9%), (3.5%, 0.6%) and (4%, 0.6%), respectively. Post-deposition annealing treatments were made in order to induce optical activation of the rare earths. Conversion or absorption of high energy photons were analyzed by photoluminescence spectroscopy. The photoluminescence spectra show that for a given temperature range in the thermal annealing process, as well as for the appropriate rare earth concentrations the activation of Yb3+ and Tb3+ is enhanced. A strong reduction of the Tb3+ emission in contrast to the Yb3+ emission in the a-SiCxOy,:Tb:Yb samples at annealing temperature at 500°C suggests a energy transfer from Tb3+ to Yb3+ ions. Copyright © 2018 VBRI Press. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Estudio del efecto del polvo y estimación de la potencia nominal en un string fotovoltaico(Universidad Nacional de Ingeniería, 2020-05-09)La cantidad de polvo depositado en la superficie de un panel depende de los parámetros ambientales. Estos son de naturaleza aleatoria (ej. humedad, velocidad del viento y temperatura ambiente) lo que dificulta su modelamiento teórico. El presente trabajo describe el efecto del polvo calculando el factor de reducción (ηpolvo) y modelando su dependencia en el tiempo. Para lograr esto, se llevó una campaña experimental en tres strings tándem (a-Si / µc-Si) de 1.15 kW ubicados en la cuidad de Lima, dividida en dos periodos de tiempo. El primer periodo, del 15.07.2016 al 04.07.2017, los tres string se limpiaron dos veces semanalmente. La potencia nominal fue calculada para los días con cielo despejado. Se encontró que entre cada string existen ligeras diferencias o mismatch en la potencia nominal, lo que se consideró estimar un factor de corrección (k) con el propósito de reajustar la potencia de salida. En la segunda etapa del 05.07.2017 al 05.07.2018, se dejó que el polvo se deposite de manera natural, estudiando el efecto del polvo en la caída energética mediante el factor de reducción. Comprender este factor será de importancia para las operaciones de mantenimiento de los strings ubicados en ese entorno especifico. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Procedimiento del cálculo de la potencia nominal de un generador fotovoltaico(Universidad Nacional de Ingeniería, 2020-05-09)La potencia nominal de un sistema fotovoltaico es un parámetro útil en la determinación de la condición en el que se encuentra el generador fotovoltaico. En el presente trabajo se siguió el procedimiento planteado por Martínez-Moreno, el cual se apoya en el modelo de Osterwald. Durante el desarrollo del procedimiento se observó el efecto de histéresis en diferente medida a lo largo de la campaña experimental. Los valores de la potencia corregida versus irradiancia diferían a lo largo del día, incluso cuando los valores de irradiancia y temperatura del módulo son similares. Lo que conllevaba a una incertidumbre en la inclusión de todos los datos. Debido a esto, se busca la adición de un filtro de los datos en el procedimiento de la estimación de la potencia nominal como complemento a lo propuesto por Martínez-Moreno en un intento de esclarecer el cálculo en generadores que presenten este comportamiento no lineal. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Puesta en marcha de un laboratorio para la caracterización de tecnologías fotovoltaicas a sol real bajo las condiciones climáticas de Lima(Universidad Nacional de Ingeniería, 2020-05-09)En este trabajo se presenta el diseño, la implementación y los primeros resultados de un Laboratorio de Investigación Fotovoltaica desarrollado en las instalaciones del Grupo de Ciencia de Materiales y Energías Renovables (MatER-PUCP) de la Pontificia Universidad Católica del Perú en colaboración con el Grupo de Investigación y Desarrollo en Energía Solar y Automática (IDEA) de la Universidad de Jaén (UJA) de España. Este laboratorio es uno de los primeros en el país con el equipamiento adecuado para la calibración y certificación de diferentes tecnologías, comerciales y emergentes, de módulos fotovoltaicos en el mercado peruano. Los resultados que se esperan obtener mediante una extensa campaña experimental, que inició en mayo del 2019, podrán ser ofertados a empresas u otras instituciones públicas, como estudios detallados del comportamiento y degradación de las diferentes tecnologías de módulos fotovoltaicos en función de las condiciones climáticas particulares de la ciudad de Lima (niveles de irradiancia y su componente difuso, temperatura de operación, humedad, distribución espectral, y polvo). - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Bandgap engineering of hydrogenated a-SiC:H thin films for photoelectrochemical water splitting applications(IOP Publishing Ltd, 2020-12-15)Abstract Bandgap engineering of a-SiC:H thin films was carried out to assess the material light absorption without compromising its photoelectrochemical water splitting capabilities. The tailoring was performed by varying the hydrogen concentration in the semiconductor and by post-deposition isochronical annealing treatments from 100 °C to 700 °C. Bandgap values were obtained by fitting the fundamental absorption region of the absorption coefficient using three different models. Differences among bandgap values extracted by these methods and its correlation with the a-SiC:H structure, demonstrate that structural features, rather than a hydrogen rearrangement or depletion, would be responsible for annealing induced optical bandgap increment. These features are taking in advantage for the bandgap engineering of a-SiC:H without changing Si-C stoichiometry. Optical bandgap values for p-doped a-SiC:H samples gradually increased from 2.59 to 2.76 eV upon performing each annealing step until 600 °C. Temperature at which an enhancement in the electric performance is observed. We believe, these results will help on the design of monolithic tandem solar cells for water splitting applications. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Strain and grain size determination of CeO2 and TiO2 nanoparticles: comparing integral breadth methods versus Rietveld, µ-Raman, and TEM(MDPI, 2021-09-01)Various crystallite size estimation methods were used to analyze X-ray diffractograms of spherical cerium dioxide and titanium dioxide anatase nanoparticles aiming to evaluate their reliability and limitations. The microstructural parameters were estimated from several integral breadth methods such as Scherrer, Monshi, Williamson–Hall, and their variants: (i) uniform deformation model, (ii) uniform strain deformation model, and (iii) uniform deformation energy density model. We also employed the size–strain plot and Halder–Wagner method. For this purpose, an instrumental resolution function of an Al2O3 standard was used to subtract the instrumental broadening to estimate the crystallite sizes and strain, and the linear regression analysis was used to compare all the models based on the coefficient of determination. The Rietveld whole powder pattern decomposition method was introduced for comparison purposes, being the best candidate to fit the X-ray diffraction data of metal-oxide nanoparticles. Refined microstructural parameters were obtained using the anisotropic spherical harmonic size approach and correlated with the above estimation methods and transmission electron microscopy images. In addition, µ-Raman spectra were recorded for each material, estimating the mean crystallite size for comparison by means of a phonon confinement model. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Strain and grain size of CeO2 and TiO2 nanoparticles: comparing structural and morphological methods(MDPI, 2021-06-07)Various crystallite size estimation methods were used to analyze X-ray diffractograms of spherical cerium dioxide and donut-like titanium dioxide anatase nanoparticles aiming to evaluate their reliability and limitations. The microstructural parameters were estimated from Scherrer, Monshi, Williamson-Hall, and their variants: i) uniform deformation model, ii) uniform strain deformation model, and iii) uniform deformation energy density model, and also size-strain plot, and Halder-Wagner method. For that, and improved systematic Matlab code was developed to estimate the crystallite sizes and strain, and the linear regression analysis was used to compare all the models based on the coefficient of determination, where the Halder Wagner method gave the highest value (close to 1). Therefore, being the best candidate to fit the X-ray Diffraction data of metal-oxide nanoparticles. Advanced Rietveld was introduced for comparison purposes. Refined microstructural parameters were obtained from a nanostructured 40.5 nm Lanthanum hexaboride nanoparticles and correlated with the above estimation methods and transmission electron microscopy images. In addition, electron density modelling was also studied for final refined nanostructures, and μ-Raman spectra were recorded for each material estimating the mean crystallite size and comparing by means of a phonon confinement model. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Silver/palladium nanofilms for SERS application: obtention and characterization(Elsevier, 2021-11-15)In this work, silver/palladium substrates for SERS applications were studied and analyzed. The electroless deposition technique was reviewed and studied step by step; for which the catalyst, activator, precursor and reducing agent were analyzed to modulate the growth of silver nanoparticles and thus obtain a greater number of SERS active sites. The substrates obtained were characterized by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The SERS application of contaminants in alcaline medium was evaluated, as an example arsenic trioxide was used, and it was detected up to 1 ppb. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revisiting the determination of the valence band maximum and defect formation in halide perovskites for solar cells: insights from highly sensitive near-UV photoemission spectroscopy(American Chemical Society, 2021-09-15)Using advanced near–UV photoemission spectroscopy (PES) in constant final state mode (CFSYS) with a very high dynamic range, we investigate the triple-cation lead halide perovskite Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 and gain detailed insights into the density of occupied states (DOS) in the valence band and band gap. A valence band model is established which includes the parabolic valence band edge and an exponentially decaying band tail in a single equation. This allows us to precisely determine two valence band maxima (VBM) at different k -vectors in the angle-integrated spectra, where the highest one, resulting from the VBM at the R -point in the Brillouin zone, is found between −1.50 to −1.37 eV relative to the Fermi energy E F . We investigate quantitatively the formation of defect states in the band gap up to E F upon decomposition of the perovskites during sample transfer, storage, and measurements: during near–UV-based PES, the density of defect states saturates at a value that is around 4 orders of magnitude below the density of states at the valence band edge. However, even short air exposure, or 3 h of X-ray illumination, increased their density by almost a factor of six and ∼40, respectively. Upon prolonged storage in vacuum, the formation of a distinct defect peak is observed. Thus, near–UV CFSYS with modeling as shown here is demonstrated as a powerful tool to characterize the valence band and quantify defect states in lead halide perovskites. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Hybrid perovskite degradation from an optical perspective: a spectroscopic ellipsometry study from the deep ultraviolet to the middle infrared(Wiley, 2021-11-21)A quantitative analysis of the thermally induced degradation of various device‐relevant multi‐cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 °C. The studied compositions are a triple cation perovskite Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3, a Rb‐containing variant Rb0.05Cs0.05(MA0.17FA0.83)0.90Pb(Br0.17I0.83)3, and a methylammonium‐free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 μm is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point‐by‐point fitting for increased sensitivity. Additionally, the formation of PbI2 and non‐perovskite δ‐CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA‐free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of δ‐CsPbI3 in addition to PbI2.
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