Analysis of SnS2 hyperdoped with V proposed as efficient absorber material

Intermediate-band materials can improve the photovoltaic efficiency of solar cells through the absorption of two subband-gap photons that allow extra electron-hole pair formations. Previous theoretical and experimental findings support the proposal that the layered SnS2 compound, with a band-gap of around 2 eV, is a candidate for an intermediate-band material when it is doped with a specific transition-metal. In this work we characterize vanadium doped SnS2 using density functional theory at the dilution level experimentally found and including a dispersion correction combined with the site-occupancy-disorder method. In order to analyze the electronic characteristics that depend on geometry, two SnS2 polytypes partially substituted with vanadium in symmetry-adapted non-equivalent configurations were studied. In addition the magnetic configurations of vanadium in a SnS2 2H-polytype and its comparison with a 4H-polytype were also characterized. We demonstrate that a narrow intermediate-band is formed, when these dopant atoms are located in different layers. Our theoretical predictions confirm the recent experimental findings in which a paramagnetic intermediate-band material in a SnS2 2H-polytype with 10% vanadium concentration is obtained

Band gap control via tuning of inversion degree in CdIn2_2S4_4 spinel

Based on theoretical arguments we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn$_2$S$_4$. Our \textit{ab initio} calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by accurate screened hybrid functional calculations.Comment: In press in Applied Physics Letters (2012); 4 pages, 2 figures, 1 tabl

Estudio de la microporosidad estrecha de carbones activados obtenidos de semilla de palma por activación química con KOH

Se estudió el desarrollo de los microporos por vía química en carbones que se obtuvieron a partir de semillas de la palma veitchia merriillii, utilizando en todos los casos una baja relación KOH/carbonizado y flujo de nitrógeno. El procedimiento de obtención fue realizado mediante dos pasos, carbonización y activación, en este último, se utilizaron temperaturas de activación crecientes de 873, 973, 1 073 y 1 173 K respectivamente. La caracterización fue llevada a cabo mediante las isotermas de adsorción de CO2 a 295 K, en un equipo de vidrio pyrex y varias válvulas de teflón, acoplado a un sistema Edward de alto vacío, el que también consta de un transductor de presión. Los resultados se compararon con los publicados por Dubinin para los carbones comerciales tipo tamiz molecular CMS4A y CMS5A y con carbones microporosos con diferentes porcentajes de quemado o burn off, obtenidos también por Dubinin a partir de cascarón de coco. Por otra parte, se estudió la influencia de la temperatura de activación y de la relación KOH/carbonizado en todos los resultados. Las conclusiones en este trabajo indican de manera general que los carbones activados obtenidos presentan volúmenes de microporos y microporosidades estrechas tan o más desarrolladas que los carbones obtenidos del mismo material activado por vía física y también mayores que los demás carbones obtenidos por Dubinin con los que fueron comparados, por lo que pueden ser utilizados como material de partida para la obtención de carbones tipo tamiz molecula

New generation of more efficient solar energy materials: Quantum modeling and experimental realizations

Trabajo presentado la XXV IUPAP Conference on Computational Physics, celebrada en Moscú (Rusia) del 20 al 24 de agosto de 2013.The intermediate band (IB) solar cell has been proposed as a novel device structure which could enhance photovoltaic efficiency, thanks to the cooperation of two sub-bandgap energy photons which allows the full excitation of an electron across the whole bandgap of a semiconductor. To realize this principle we have proposed in recent years, on the basis of quantum mechanical calculations, several materials where a metal or heavy element substitutes an atom in a known semiconductor with appropriate band gap, creating inside the band gap a partially filled band. This new intermediate band, allows the absorption of low energy photons inside the gap increasing the photo-current and also maintaining the photo-voltage. We present here compounds derived from different families of sulphides semiconductors, mainly spinels thin film and layered compounds: - In2S3 and other sulphides containing octahedral In. The V-doped In2S3 material is particularly promising. We have synthesized it in nanocrystalline form and shown that its optical absorption spectrum has the features predicted by quantum calculations3 . Recent photocatalytic tests made with it show that the V dopant extends its spectral response down to the IR range without increasing recombination. - Octahedral SnIV layered sulphide and other similar compounds show also, according to theoretical modeling the formation of an IB with the desired characteristics when transition metals are introduced at Sn sites. The Van der Waals cleavage plane (0001) of these layered semiconductors is characterized by hexagonal arrays of close packed chalcogenide ions which are covalently bound within X-M-X sandwiches. This is an ideal substrate to study fundamental aspects of the metal/semiconductor interaction. The experimental synthesis of such sulphide show optical absorption spectra matching again the expectations for an IB material4 . An overview of these systems, including results obtained on them using high level, state-of-the-art quantum calculation methods will be presented. Experimental results obtained for such novel IB materials matching in all cases the theoretical predictions.Peer Reviewe

More Efficient Photovoltaic Materials by Metal Substitution in Sulphides Compounds: Theoretical Predictions and Experimental Results

Trabajo presentado en EUROMAT: European Congress and Exhibition on advanced materials and processes, celebrado en Sevilla (España) del 8 al 13 de septiembre de 2013.The introduction of a properly chosen transition metal at high concentration into an octahedral semiconductor provides in-gap delocalized and partially occupied levels required by the Intermediate Band (IB) concept. We have verified with accurate DFT calculations including Van der Waals forces, that layered semiconductors as SnS2 or ZnIn2S4 can provide this situation when an octahedral cation in their structure is partially substituted by an element such as vanadium. The Van der Waals cleavage plane (0001) of these layered semiconductors is characterized by hexagonal arrays of close packed chalcogenide ions which are covalently bound within X-M-X sandwiches. This is an ideal substrate to study fundamental aspects of the metal/semiconductor interaction. Experimental work made via wet chemistry methods verifies that new absorption features appear in the optical absorption spectrum which matches the predicted DFT-based theoretical absorption results. Moreover, simple photocatalytic tests with these two materials, show spectral responses which evidence in both cases a very substantial ability to use sub-bandgap photons to drive electron and hole transfers at the material interface with scarce efficiency degradation by recombination effects. The results show that these materials have the appropriate characteristics for building photovoltaic devices of boosted efficiency using the whole range of the visible light spectrumPeer Reviewe

Material de banda intermedia basado en un compuesto semiconductor de tipo calcogenuro de estaño

Material de banda intermedia basado en un compuesto semiconductor de tipo calcogenuro de estaño. La invención se refiere a compuestos formados mediante la introducción, dentro de un semiconductor de partida que es de tipo calcogenuro de estaño tetravalente octaédricamente coordinado, de un elemento de transición en posición octaédrica, para la fabricación de materiales o dispositivos para aplicaciones fotónicas. El elemento de transición genera una banda intermedia parcialmente ocupada separada de las de valencia y conducción del semiconductor de partida, según resulta de cálculos mecanocuánticos. Esto posibilita obtener, por absorción de dos fotones de energía inferior a la anchura de la banda prohibida del semiconductor de partida, un resultado equivalente al que se consigue absorbiendo un fotón de energía superior a dicha anchura en ausencia de banda intermedia. Usando el material de la invención se obtiene un mayor rendimiento y mejores prestaciones en diversos dispositivos de tipo fotovoltaico, fotocatalítico, fotoelectroquímico, optoelectrónico o de conversión fotónica.Peer reviewedConsejo Superior de Investigaciones Científicas (España), Universidad Politécnica de MadridA1 Solicitud de patentes con informe sobre el estado de la técnic

New generation of materials for more efficient solar energy use: Quantum modeling and experimental realizations

Trabajo presentado en el Simposio en Energía y Sostenibilidad; XXXIV Reunión Bienal de la Real Sociedad Española de Física, celebrado en Valencia (España) del 15 al 19 de julio de 2013.The intermediate band (IB) solar cell has been proposed as a novel device structure which could enhance photovoltaic efficiency, thanks to the cooperation of two sub-bandgap energy photons which allows the full excitation of an electron across the whole bandgap of a semiconductor. To realize this principle we have proposed in recent years, on the basis of quantum mechanical calculations, several materials where a metal or heavy element substitutes an atom in a known semiconductor with appropriate band gap, creating inside the band gap a partially filled band. This new intermediate band, allows the absorption of low energy photons inside the gap increasing the photo-current and also maintaining the photo-voltage. We present here compounds derived from different families of sulphides semiconductors, mainly spinels thin film and layered compounds: - In2S3 and other sulphides containing octahedral In. The V-doped In2S3 material is particularly promising. We have synthesized it in nanocrystalline form and shown that its optical absorption spectrum has the features predicted by quantum calculations3 . Recent photocatalytic tests made with it show that the V dopant extends its spectral response down to the IR range without increasing recombination. - Octahedral SnIV layered sulphide and other similar compounds show also, according to theoretical modeling the formation of an IB with the desired characteristics when transition metals are introduced at Sn sites. The Van der Waals cleavage plane (0001) of these layered semiconductors is characterized by hexagonal arrays of close packed chalcogenide ions which are covalently bound within X-M-X sandwiches. This is an ideal substrate to study fundamental aspects of the metal/semiconductor interaction. The experimental synthesis of such sulphide show optical absorption spectra matching again the expectations for an IB material4 . An overview of these systems, including results obtained on them using high level, state-of-the-art quantum calculation methods will be presented. Experimental results obtained for such novel IB materials matching in all cases the theoretical predictions.Peer Reviewe

Separation of an aqueous mixture of 6-kestose/sucrose with zeolites: A molecular dynamics simulation

Extra-large pore zeolites are a small subset (21) among the whole list of 253 zeolites available. The discovery of new low-glycemic sugars is very attractive as new healthy additives in the food field. This is the case of the 6-kestose. In the present case, it appears in a mixture in aqueous solution together with sucrose, the separation of the mixture being necessary. For this, we have focused on using certain zeolites with adequate pore sizes that allow the separation of this mixture, considering that since the molecular size of 6-kestose is greater than sucrose, it is necessary to promote the sorption of the latter, so that the first can be purified. After a computational screening of micropores of the 253 IZA zeolites, 11 zeolites were selected. Of these, 3 extra-large pore zeolites (AET, DON, ETR) have been proposed, which were analyzed in-depth through a molecular dynamics study considering the external surface. The results show that DON presents the most promising theoretical results for a selective sucrose/6-kestose separation.We thank MICINN of Spain for funding through projects RTI2018-101784-B-I00, RTI2018-101033-B-I00, SEV-2016-0683 as well as ASIC-UPV and CESGA for computational facilities. IBL and PGI gratefully acknowledge CSIC for a JAE-Intro fellowship. AM thanks Generalitat Valenciana for the predoctoral fellowship GRISOLIAP/2019/084

Metal-substituted octahedral sulphides for more efficient PV: theoretical modeling and experimental verification of sub-bandgap photon use

Trabajo presentado en el E-MRS 2013 Spring Meeting, celebrado en Estrasburgo (Francia) del 27 al 31 de mayo de 2013.We present results on metal-containing sulphides which we propose, based on ab-initio DFT calculations, as having Intermediate Band (IB) electronic characteristics like those allowing the construction of highly efficient PV cells. We synthesized V-containing SnS2, one of those systems, and have proven with a photocatalytic test that sub-bandgap photons generate in it electrons and holes. We check that Van der Waals interactions between the X-M-X sandwiches parallel to the (0001) plane in its structure must be included in its DFT modelling to get correct results. We model also the stability of different V-doping configurations proving that those which lead to an IB and reproduce the observed paramagnetism are metastable (the most stable configuration leads to V-V pairing), so that nonequilibrium synthesis methods are essential to prepare a material with an IB. We also study V-doped ZnIn2S4, another Van der Waals-layered structure showing an IB in the DFT calculations. We prepared this material, which also displays in the optical spectrum sub-bandgap photon absorption matching the DFT results, and have carried out on it the same photocatalytic test, which shows as well photoactivity with sub-bandgap photons, but less marked than in the cases of V:SnS2 or V:In2S3, the best of our systems to date. Finally we report how a photocatalytic test using dissolved compounds which react selectively with trapped electron or hole species can check separately the behaviour of these latter.Peer Reviewe