Effect of the electrophoretic deposition of Au NPs in the performance CdS QDs sensitized solar cells

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability alternative for next generation of solar cells, and metallic nanoparticles had shown to be a good alternative to improve specific parameters in such kind of devices. In the present work, it is showed the systematic study of the effect of electrophoretic gold nanospheres (Au NPs) with cadmium sulfide Quantum Dots (CdS QDs) sensitized TiO2 solar cells. Au NPs were added by electrophoretic deposition at several times (0.5, 2.5 and 7.5 minutes) and CdS QDs were deposited by a Successive Ionic Layer Absorption and Reaction (SILAR) method. Electrophoretic deposition allowed to significantly decrease the Au NPs deposition times respect previously reported methods. The results show that Au NPs reduce the photocurrent (from 9.85 to 9.44 mA/cm2) at the same time that increase the open circuit voltage (Voc) (from 575 to 618 mV) and the Fill Factor (FF) (from 46 to 51%) which result in a final increase of the photoconversion efficiency (η) (from 2.63 to 2.96% for 0.5 min of deposit). A systematic characterization permitted to identify the origin of the variations observed in the solar cell parameters with and without Au NPs. Incident Photon to Current conversion efficiency (IPCE) demonstrate that the Au NPs reduces the amount of light that reach the CdS QDs and Impedance Spectroscopy (IS) analysis, indicates a downshift in the TiO2 conduction band (CB) and decreases the recombination processes, resulting in the observed increase in the FF and Voc.We acknowledge financial support from CONACYT through grant 134111, the UC-MEXUS program grant 00007, the European Community Seven Framework Program (FP7- 428 NMP-2010-EU-MEXICO), CIO-UGTO 2013–2015 and the CEMIE-Solar (04002) consortium. D. Esparza, and A. Ceja acknowledge scholarship from CONACYT and thanks to Maria Christian Albor for SEM and EDS analysis. Isaac Zarazúa thanks to CONACYT for the postdoctoral fellow

Operating Mechanisms of Mesoscopic Perovskite Solar Cells through Impedance Spectroscopy and J-V Modeling

The performance of perovskite solar cell (PSC) is highly sensitive to deposition conditions, the substrate, humidity, and the efficiency of solvent extraction. However, the physical mechanism involved in the observed changes of efficiency with different deposition conditions has not been elucidated yet. In this work, PSCs were fabricated by the antisolvent deposition (AD) and recently proposed air-extraction antisolvent (AAD) process. Impedance analysis and J–V curve fitting were used to analyze the photogeneration, charge transportation, recombination, and leakage properties of PSCs. It can be elucidated that the improvement in morphology of perovskite film promoted by AAD method leads to increase in light absorption, reduction in recombination sites, and interstitial defects, thus enhancing the short-circuit current density, open-circuit voltage, and fill factor. This study will open up doors for further improvement of device and help in understanding its physical mechanism and its relation to the deposition methods

Preparación de nanocristales funcionalizados de ZrO2:Er -Yb y ZrO2:Eu para aplicaciones fotónicas

Se prepararon nanocristales fotoluminiscentes de ZrO2:Er, ZrO2:Er-Yb y ZrO2:Eu por el método de sol-gel y precipitación usando dos tipos de surfactantes, el CTAB catiónico y el Pluronic P127 no iónico. La estructura cristalina resultante depende de la temperatura de calcinado y del tipo de ion dentro de la estructura de la zirconia. Se prepararon nanocristales de tamaño promedio desde 30 hasta 90 nm por el método de sol-gel y nanocristales de 18 nm hasta 50 nm por el método de precipitación. Al utilizar CTAB, la mejor señal emitida en el visible, centrada en 550 nm, fué obtenida de los nanocristales de ZrO2:Er utilizando una relación molar CTAB/ZrO2=0.2. En este caso se incrementó la emisión fotoluminiscente en un 300% con respecto a la muestra preparada sin utilizar surfactante. Al utilizar Pluronic, la mejor señal emitida fue obtenida con los nanocristales de ZrO2:Er preparados a una relación molar Pluronic/ZrO2=0.0082. En este caso de se incrementó en un orden de magnitud la señal emitida en luz verde con respecto a la muestra sin surfactante. En el caso de los nanocristales de ZrO2:Er-Yb se incrementaron otras bandas como es la emisión en 654 nm, en 1040 nm, y la banda en 1.5 µm en aproximadamente un 80%. Los resultados mostraron que los OH ´s contenidos en las muestras, que tienen bandas de absorción centradas en 3600-3800 cm-1, son los que afectan más a las propiedades ópticas y no el tamaño de la nanopartícula o la estructura cristalina. Para mejorar la biocompatibilidad y las propiedades ópticas, se revistieron con SiO2 los nanocristales de ZrO2:Er y ZrO2:Eu, preparados con el método sol-gel y precipitación, respectivamente. Se incrementó la señal emitida en un 100% para los nanocristales preparados de ZrO2:Er, debido a que la silica pasiva los defectos de la superficie. La luminiscencia de los nanocristales de ZrO2:Eu disminuyó en un 30%, siendo esto probablemente debido a que la capa de sílica absorbe la longitud de onda de excitación UV, la cual es diferente a la longitud de onda de excitación del Er (IR), También puede ser posible que el decremento de la luminiscencia dependa del grosor del revestimiento de SiO2

Surface enhanced Raman spectroscopy of phenolic antioxidants: A systematic evaluation of ferulic acid, p-coumaric acid, caffeic acid and sinapic acid

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful surface-sensitive technique to study the vibrational properties of analytes at very low levels of concentration. In particular, detection of bioactive molecules, specifically antioxidants, is an area of interest to gain insights into the reproducible and quantitative SERS-determination. In this study, SERS measurements were systematically evaluated for ferulic acid, p-coumaric acid, caffeic acid and sinapic acid. The study objective in this research was to: 1) prepare and characterize SERS-active silver colloids; 2) cluster the as-obtained colloids through Principal Component Analysis on the basis of concentration and nanoparticle size; and 3) develop a highly sensitive SERS-based method for phenolic antioxidant detection. The reliability of the proposed method was demonstrated through detection of the phenolic antioxidants evaluated at low levels of concentration. In particular, sinapic acid was evaluated for the first time, with a limit of detection of 2.5 × 10−9 M.acceptedVersio

Enhanced Photovoltaic Performance of Mesoscopic Perovskite Solar Cells by Controlling the Interaction between CH3NH3PbI3 Films and CsPbX3 Perovskite Nanoparticles

We report the incorporation of all-inorganic highly stable CsPbX3 (X = I, Br) based perovskite nanoparticles (NPs) on top of a bulk CH3NH3PbI3perovskite thin film. This design utilizes the photogeneration ability of perovskite NPs and also improves the interfacial charge transport which happens to be a critical factor in deciding the photovoltaic performance of any solar cell device. With variation in the lead halide (PbX2, X = I, Br, Cl) content, the synthesized CsPbX3 NPs shows tunable band-edge position and fluorescence characteristics. The interaction of all inorganic NPs with the bulk perovskite resulted in improved hole injection and electron blocking characteristics leading to enhanced light harvesting efficiency. The CsPbBr3 and CsPbI3 perovskite NPs were used for fabricating the bulk-NP structure due to their better absorption and valence band edge characteristics. The inclusion of CsPbI3 NPs on top of the bulk perovskite showed a significant increment in the power conversion efficiency of 28%, in comparison with a reference sample without NPs, due to significant improvements in current density, open circuit voltage, and fill factor

Synthesis of Alloyed CdxZn1-xS Quantum Dots for Photovoltaic Applications

This article describes the synthesis of Cdx Zn1- x S quantum dots prepared using the successive ionic layer adsorption and reaction method and incorporated into a photovoltaic device. The Cdx Zn1- x S quantum dots exhibit good optical and electrical properties. The photovoltaic device has the configuration TiO2 /Cd0.75 Zn0.25 S1 /ZnS. A photoconversion efficiency of 3.6% was obtained with this device. This efficiency corresponds to a 16% relative increment compared with a reference sample with the con- figuration TiO2 /Cd1 Zn0 S1 /ZnS. The improvement is associated with an increment in the open-circuit voltage (Voc) from 0.517 to 0.725 V. The corresponding short-circuit current density (Jsc) was reduced from 12.15 to 11.66 mA cm!2. Electrochemical impedance spectroscopy analyses confirm that the behavior of the device was due to a recombination rate reduction obtained as a result of surface passivation between the TiO2 layer and the CdxZnx-1S QDs interface