Cette recherche a été financée dans le cadre du Centre pour l&#39;énergie nanosciences, un centre de recherche Frontier énergie financé par le Département américain de l&#39;énergie, Bureau de la science sous Award Nombre DE-SC0001013. Nous tenons également à remercier le Dr Max Zhang et Yang Jianhua Dr de HP Labs pour leur aide sur TiO 2 pulvérisation du film et de la mesure des indices de réfraction.

1. Préparer le Polydimethylsiloxane Blank (PDMS) Substrat pour nanoimpression Mold <ol><li> Processus Silicon traitement Wafer <ol><li> Nettoyer une tranche de silicium de 4 pouces par rinçage avec de l&#39;acétone, le methanol et l&#39;isopropanol. </li><li> Soufflez sécher à l&#39;aide du pistolet d&#39;azote. </li><li> Nettoyer à l&#39;aide d&#39;une solution de piranha (3: 1 de mélange de l&#39;acide sulfurique avec 30% de peroxyde d&#39;hydrogène) par trempage pendant 15 min à l&#39;intérieur. </li><li> Rincez avec de l&#39;eau DI. Séchez à l&#39;aide du pistolet d&#39;azote. </li><li> Placer la plaque dans un dessiccateur en verre. Ajouter une goutte (20 gouttes = 1 ml) d&#39;agent (trichlorosilane) libérant dans le dessiccateur. </li><li> Pomper le dessiccateur jusqu&#39;à ce que la jauge indique -762 Torr et attendre pendant 5 heures. </li><li> Prendre la galette, qui a été traitée avec un agent de libération. </li></ol></li><li> Préparation de PDMS Film (Utilisé comme moisissure dans les nano-impression) <ol><li> Peser 10 g de silicone élastomère de base et 1 g d&#39;agent de durcissement. </li><li> Ajoutez-les dans le même récipient en verre. </li><li> Stir et mélanger avec une baguette de verre pendant 5 minutes. </li><li> Mettre le mélange dans un dessiccateur à vide jusqu&#39;à ce que la jauge indique -762 Torr pour pomper toutes les bulles d&#39;air piégées. </li><li> Les répartir uniformément sur la plaquette de silicium de 4 pouces traitée. </li><li> Faire cuire au four la plaquette sur le dessus de PDMS dans le four à vide pendant 7 heures à 80 ° C pour durcir le film de PDMS. </li></ol></li></ol> 2. Préparer le moule nano-impression (reproduction de la moule principal) <ol><li> Spin douze gouttes (20 gouttes = 1 ml) de UV curable résister (15,2%) sur une plaquette de silicium vierge propre pendant 30 secondes à 1500 tours par minute. </li><li> Retirer délicatement un morceau de film PDMS au large de la plaquette de silicium traité. </li><li> Mettez le film sur le PDMS UV curable résister et laisser absorber résister à l&#39;UV pendant 5 min, puis l&#39;éplucher au loin. </li><li> Répétez 2.1-2.3 sur le même film PDMS pour deux fois. Absorber résister à l&#39;UV pendant 3 min et 1 min respectivement. </li><li> Placez le film PDMS (après UV trois fois résister à l&#39;absorption) sur un moule maître de silicium. </li><li> Le mettre dans une chambre à environnement d&#39;azote. </li><li> Allumer lampe UV pour durcir l&#39;échantillon pendant 5 min. </li><li> Décoller le film de PDMS. Résistez à l&#39;UV durci sur les PDMS gardera le modèle négatif du moule maître. </li><li> Utilisation RF plasma O 2 pour traiter le moule PDMS. (Puissance RF: 30 W, pression: 260 mTorr, le temps: 1 min) </li><li> Placer le moule PDMS dans une chambre à vide avec une goutte (20 gouttes = 1 ml) d&#39;agent de libération pendant 2 heures. </li></ol> 3. nanoimpression Motif Transfert <ol><li> Spin huit gouttes (20 gouttes = 1 ml) de PMMA (996k, 3,1%) sur le substrat pour être imprimé pendant 50 sec à 3500 rpm. </li><li> Cuire sur une plaque chauffante pendant 5 min à 120 ° C. </li><li> Attendez que l&#39;échantillon refroidir. </li><li> Spin huit gouttes (20 gouttes = 1 ml) de UV curable résistent (3,9%) sur le même substrat. </li><li> Placez le moule PDMS (préparé à l&#39;étape 2) sur l&#39;échantillon (à la fois avec UV résister et PMMA). </li><li> Le mettre dans une chambre à environnement d&#39;azote.</li><li> Allumez la lampe UV pour durcir pendant 5 min. </li><li> Peel le moule PDMS hors de l&#39;échantillon et le motif sur le moule PDMS est transféré à l&#39;échantillon. </li></ol> 4. Cr procédé lift-off <ol><li> Attaque ionique réactive de la couche résiduelle UV et résister PMMA Remarque: Le POS pour la machine ICP peut être trouvé à https://www.nanocenter.umd.edu/equipment/fablab/sops/etch-07/Oxford%20Chlorine%20Etcher%20SOP.pdf <ol><li> Se connecter la machine ICP RIE. </li><li> Déposez un wafer de silicium de 4 pouces. Exécutez la recette propre pour 10 min. </li><li> Prenez la plaquette de silicium vierge sur. </li><li> Monter l&#39;échantillon sur une autre tranche de silicium propre et le charger dans la machine. </li><li> Exécutez résister à l&#39;UV recette gravure pendant 2 min (la recette peut être trouvé dans le tableau 1). </li><li> Prenez l&#39;échantillon hors. Déposez un wafer de silicium de 4 pouces. Re-exécuter la recette propre (peut être trouvé dans le tableau 1) pendant 10 min. </li><li> Monter l&#39;échantillon sur une plaquette de silicium propreet la charger dans la machine. </li><li> Exécutez la recette gravure PMMA (peut être trouvé dans le tableau 1) pendant 2 min. Note: Maintenant, le résiduel de resist a été gravée et le substrat est exposée. </li></ol></li><li> Cr E-faisceau d&#39;évaporation <ol><li> Connectez-vous à l&#39;évaporateur à faisceau électronique. </li><li> Chargez la source de métal Cr et échantillon dans la chambre. </li><li> Réglez l&#39;épaisseur (20 nm) et la vitesse de dépôt (0,03 nm / sec). </li><li> Pomper la chambre jusqu&#39;à ce que le vide nécessaire (10 -7 Torr) est atteint. </li><li> Lancer le processus de dépôt. </li><li> Prenez l&#39;échantillon après les finitions de dépôt. </li></ol></li><li> CR Soulevez-off Procédure <ol><li> Immerger l&#39;échantillon dans de l&#39;acétone avec agitation ultrasonique pendant 5 min. </li><li> Nettoyer l&#39;échantillon en rinçant avec de l&#39;acétone, le methanol et l&#39;isopropanol. Remarque: Le Cr évaporée sur le resist seront ramassées et un masque pour Cr substrat gravure est formé. </li></ol></li></ol> 5. TiO 2 Deposition <ol><li> échantillon de charge. </li><li> Définissez les paramètres pour le courant la machine de pulvérisation magnétron directe <ol><li> Utilisez une pression de chambre de 1,5 mTorr, Ar débit de 100 sccm et une puissance de pulvérisation de 130 W. </li><li> Utiliser une température de 27 ° C et une vitesse de rotation de phase de 20 tours par minute. </li></ol></li><li> Lancer le processus de pulvérisation et arrêter à l&#39;épaisseur souhaitée. </li><li> Prendre l&#39;échantillon et à recuire le film de TiO 2 dans un environnement d&#39;oxygène à 300 ° C pendant 3 heures. </li></ol> 6. High Contrast caillebotis Gravure <ol><li> Se connecter la machine plasma à couplage inductif (ICP) gravure ionique réactive (RIE). </li><li> Gravure de TiO 2 <ol><li> Déposez un wafer de silicium de 4 pouces. </li><li> Démarrer et exécuter la recette propre (peut être trouvé dans le tableau 1) pendant 10 min. </li><li> Décharger charger la plaquette vierge et charger l&#39;échantillon avec masque Cr. </li><li> Réglez le temps de gravure. Lancer TiO 2 gravure recette. Le processus de gravure volonté autoarrêter automatiquement. </li><li> Décharger l&#39;échantillon. </li></ol></li><li> SiO 2 Gravure <ol><li> Répétez l&#39;étape 5.2, sauf utiliser la gravure recette SiO 2. </li></ol></li></ol> 7. Réflexion mesure <ol><li> Connectez-vous et mettez le système de mesure. </li><li> Placez le miroir étalon de réflexion sur le support d&#39;échantillon et aligner le chemin optique. </li><li> Calibrer le système pour le 100% de réflectance. </li><li> Enlever le miroir étalon de réflexion et placer le HCG. </li><li> Mesurer la réflectance de la HCG. </li><li> Sauvegardez les données et se connecter sur le système de mesure. </li></ol>

<ol>
	<li>Horne, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Solid+500+Sun+Compound+Concentrator+PV+Design.">A Solid 500 Sun Compound Concentrator PV Design.</a> Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on. , 694-697 (2006).</li><li>Guter, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current-matched+triple-junction+solar+cell+reaching+41.1%+conversion+efficiency+under+concentrated+sunlight.">Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight.</a> Applied Physics Letters. 94, 223504 (2009).</li><li>Shockley, W., Queisser, H. 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Express. 20, 10888-10895 (2012).</li><li>Chou, S. Y., Krauss, P. R., Renstrom, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoimprint+lithography.">Nanoimprint lithography.</a> Journal of Vacuum Science &amp; Technology B: Microelectronics and Nanometer Structures. 14, 4129-4133 (1996).</li><li>Namiki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+FDTD+algorithm+based+on+alternating-direction+implicit+method.+Microwave+Theory+and+Techniques.">A new FDTD algorithm based on alternating-direction implicit method. Microwave Theory and Techniques.</a> IEEE Transactions on. 47, 2003-2007 (1999).</li><li>Moharam, M. G., Gaylord, T. 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H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-50+nm+period+patterns+with+EUV+interference+lithography.">Sub-50 nm period patterns with EUV interference lithography.</a> Microelectronic Engineering. 67, 56-62 (2003).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hybrid+nanoimprint&#8722;+soft+lithography+with+sub-15+nm+resolution.">Hybrid nanoimprint&#8722; soft lithography with sub-15 nm resolution.</a> Nano letters. 9, 2306-2310 (2009).</li><li>Yu, Z., Chen, L., Wu, W., Ge, H., Chou, S. 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The authors have nothing to disclose.

Tout d&#39;abord, la qualité du film de TiO 2 est très important pour la performance de HCG. Le pic de réflectance sera plus élevé si le film de TiO 2 a moins de perte et de la rugosité de surface. Le film de TiO 2 avec un indice de réfraction supérieur est également favorable car le mode confinement optique sera renforcée par un contraste plus élevé de l&#39;indice, ce qui peut donner lieu à une plus plate et plus large bande de réflectance en HCG. <p class="jove_conte...

Notre société moderne ne survivra pas sans bouger une partie importante de la consommation d&#39;énergie de sources d&#39;énergie renouvelables. Pour ce faire, nous devons trouver un moyen de récolter de l&#39;énergie renouvelable à un coût moindre que les sources d&#39;énergie à base de pétrole dans un avenir proche. L&#39;énergie solaire est l&#39;énergie renouvelable la plus abondante sur terre. Malgré que beaucoup de progrès ont été accomplis dans la récolte de l&#39;énergie solaire, il est encore très difficile de rivaliser avec les sources d&#39;énergie à base de pétrole. Améliorer l&#39;efficacité des cellules solaires est l&#39;un des moyens les plus efficaces pour réduire le coût du système d&#39;exploitation de l&#39;énergie solaire. Lentilles optiques et des réflecteurs paraboliques sont généralement utilisés dans photovoltaïques plus concentré (CPV) 1 d&#39;atteindre une concentration élevée de l&#39;incidence de l&#39;énergie solaire sur les cellules solaires de petite surface, de sorte qu&#39;il est économiquement viable d&#39;exploiter tandem cher cellules solaires multi-jonctions 2 dans systèmes CPV, et pour maintenir un raisonnablecoûter en même temps. Cependant, pour la plupart des systèmes photovoltaïques non concentrés, qui nécessitent généralement une grande surface tranche de cellules solaires, les cellules solaires tandem à coût élevé ne peuvent pas être incorporé, même si elles ont généralement une réponse de spectre solaire plus large et un rendement de conversion global supérieur à la simple jonction des cellules solaires 3. Récemment, avec l&#39;aide de parallèles l&#39;optique de fractionnement du spectre (c.-à-dispersif élément), la technologie photovoltaïque de fractionnement du spectre parallèle 4 a permis que la couverture du spectre similaire ou meilleure et l&#39;efficacité de conversion peuvent être atteints sans l&#39;aide des cellules solaires en tandem cher. Le spectre solaire peut être divisé en différentes bandes et chaque bande peut être absorbée et convertie en électricité par des cellules solaires à jonction unique spécialisés. De cette façon, les cellules solaires tandem coûteux dans les systèmes de CPV peut être remplacée par une distribution parallèle d&#39;une seule jonction cellule solaires sans aucun compromis sur la performance. L&#39;élément dispersif qui a été conçu dans ce rapport peut être appliqué dans un système de CPV réfléchissante (qui est basé sur des réflecteurs paraboliques), pour réaliser le partage du spectre parallèle pour l&#39;amélioration de l&#39;efficacité de conversion solaire-électrique et un coût réduit. Multicouches grilles de contraste élevé (hCG) 5 est utilisé comme élément dispersif en concevant chaque couche de HCG pour travailler comme une bande réflecteur optique. Les structures et les paramètres de l&#39;élément dispersif sont numériquement optimisés. En outre, la fabrication de grilles de contraste élevé de l&#39;élément dispersif à l&#39;aide de diélectrique (TiO 2) de pulvérisation, la lithographie par nanoimpression 6 et gravure ionique réactive est étudiée et démontrée.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>184 SILICONE ELASTOMER KIT</td>
			<td>SYLGARD</td>
			<td></td>
			<td>Polydimethylsiloxane (PDMS)</td>
		</tr>
		<tr>
			<td>4-inch silicon wafer</td>
			<td>Universitywafer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>4-inch fused silica wafer</td>
			<td>Universitywafer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(methyl methacrylate)</td>
			<td>SIGMA-ALDRICH</td>
			<td align="right">182265</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-curable resist</td>
			<td></td>
			<td></td>
			<td>Nor available on market</td>
		</tr>
		<tr>
			<td>PlasmaLab System 100</td>
			<td>Oxford Instruments</td>
			<td></td>
			<td>ICP IRE machine</td>
		</tr>
		<tr>
			<td>UV curing system for nanoimprint fabrication</td>
			<td></td>
			<td></td>
			<td>Not available on market</td>
		</tr>
		<tr>
			<td>Ocean Optics HR-4000&#160;</td>
			<td>Ocean Optics</td>
			<td>HR-4000</td>
			<td>Spectrometer with normal detector</td>
		</tr>
		<tr>
			<td>Lambda 950 UV / VIS</td>
			<td>PerkinElmer</td>
			<td></td>
			<td>spectrometer with hemisphere intergration detector</td>
		</tr>
		<tr>
			<td>JSM-7001F-LV</td>
			<td>JEOL</td>
			<td></td>
			<td>Field emission SEM</td>
		</tr>
		<tr>
			<td>DC magnetron sputtering machine</td>
			<td></td>
			<td></td>
			<td>Equipment is in HP labs, who helped us to sputter the TiO2</td>
		</tr>
		<tr>
			<td>Metal e-beam evaporator</td>
			<td>Temescal</td>
			<td>BJD-1800</td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication of high contrast gratings for the spectrum splitting dispersive element in a concentrated photovoltaic system

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

La figure 1 illustre la mise en oeuvre de l&#39;élément dispersif (grille multicouche à haute propriété de contraste (HCG)) dans un système photovoltaïque concentré. La lumière du soleil est réfléchie par le premier miroir primaire et empiète sur l&#39;élément dispersif réfléchissant, où le faisceau est réfléchi et divisé en différentes bandes de longueurs d&#39;onde différentes. Chaque groupe se empiéter sur un certain emplacement sur le réseau de cellules solaires pour la meill...

Watch this Scientific Journal Video about Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System at JoVE.com

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

Fabrication de réseaux de contraste élevé pour le fractionnement du spectre dispersif élément d&#39;un système photovoltaïque à concentration

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

fabrication-high-contrast-gratings-for-spectrum-splitting-dispersive

Research

JoVE Journal

Engineering

10.6K vues.  University of Sothern California. The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance. 

Vidéo: Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Electron Canalisation imagerie de contraste pour Rapid III-V hétéroépitaxiale Caractérisation

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Recherche

Ingénierie

Energy Dispersive X-ray Tomography for 3D Elemental Mapping of Individual Nanoparticles

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial resolution, and is even capable of providing atomically resolved elemental maps. In this technique, a highly focused electron beam is incident upon a thin sample and the energy of emitted X-rays is measured in order to determine the atomic species of material within the beam path. This elementally sensitive spectroscopy technique can be extended to three dimensional tomographic imaging by acquiring multiple spectrum images with the sample tilted along an axis perpendicular to the electron beam direction.
Elemental distributions within single nanoparticles are often important for determining their optical, catalytic and magnetic properties. Techniques such as X-ray tomography and slice and view energy dispersive X-ray mapping in the scanning electron microscope provide elementally sensitive three dimensional imaging but are typically limited to spatial resolutions of &gt; 20 nm. Atom probe tomography provides near atomic resolution but preparing nanoparticle samples for atom probe analysis is often challenging. Thus, elementally sensitive techniques applied within the scanning transmission electron microscope are uniquely placed to study elemental distributions within nanoparticles of dimensions 10-100 nm.
Here, energy dispersive X-ray (EDX) spectroscopy within the STEM is applied to investigate the distribution of elements in single AgAu nanoparticles. The surface segregation of both Ag and Au, at different nanoparticle compositions, has been observed.

The use of energy dispersive X-ray tomography in the scanning transmission electron microscope to characterize elemental distributions within single nanoparticles in three dimensions is described.

Tomographie à dispersion d&#39;énergie de rayons X pour la 3D élémentaire Cartographie des nanoparticules individuelles

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Rédaction de Bragg dans les fibres multipaires

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

Fabrication de nanocristaux dispositifs photovoltaïques inorganiques entièrement Solution transformés

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

Recombinaison Dynamics photovoltaïques en couches minces de matériaux par résolution temporelle Micro-ondes Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

Challenges in Rheological Characterization of Highly Concentrated Suspensions &amp;#8212; A Case Study for Screen-printing Silver Pastes

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

Défis à rhéologique Caractérisation des concentrés - Suspensions très Une étude de cas pour la sérigraphie argent Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

Fabrication à haute température de nanostructurés yttriée-Zircon (YSZ) par scellants<em&gt; In Situ</em&gt; Carbon Templating xérogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

Détecter la Distribution de chlorure soluble dans l’eau de la pâte de ciment d’une manière de haute précision

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Method for Recording Broadband High Resolution Emission Spectra of Laboratory Lightning Arcs

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional camera film methods and then digital camera technology, from which several important characteristics have been derived. However, such work has always been limited due to the inherently random and non-repeatable nature of natural lightning events in the field. Recent developments in lightning test facilities now allow the reproducible generation of lightning arcs within controlled laboratory environments, providing a test bed for the development of new sensors and diagnostic techniques to understand lightning mechanisms better. One such technique is a spectroscopic system using digital camera technology capable of identifying the chemical elements with which the lightning arc interacts, with these data then being used to derive further characteristics. In this paper, the spectroscopic system is used to obtain the emission spectrum from a 100 kA peak, 100 &#181;s duration lightning arc generated across a pair of hemispherical tungsten electrodes separated by a small air gap. To maintain a spectral resolution of less than 1 nm, several individual spectra were recorded across discrete wavelength ranges, averaged, stitched, and corrected to produce a final composite spectrum in the 450 nm (blue light) to 890 nm (near infrared light) range. Characteristic peaks within the data were then compared to an established publicly available database to identify the chemical element interactions. This method is readily applicable to a variety of other light emitting events, such as fast electrical discharges, partial discharges, and sparking in electrical equipment, apparatus, and systems.

Emission spectroscopy techniques have traditionally been used to analyze inherently random lightning arcs occurring in nature. In this paper, a method developed to obtain the emission spectroscopy from reproducible lightning arcs generated within a laboratory environment is described.

Méthode d'enregistrement des spectres d'émission à haute résolution à large bande des arcs de foudre de laboratoire

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flux-aidé diélectrophorèse : Une méthode Low Cost pour la Fabrication des dispositifs de nanofils traitable-Solution Haute Performance

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...