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In this work, we report on improving efficiency of DopLa cells fabricated on p-type substrates. This type of solar cells has all the highly-doped regions based on laser doping from dielectric films resulting in a very simple fabrication process. Depending on the dopant type, emitter regions or high/low doping junctions related to base contacts can be created. The emitter regions are located at the rear surface in order to be contacted by a continuous metal film without penalizing in shadowing losses, while the front surface shows a typical finger grid configuration with the base contacts under the metal. In a previous work, the reported efficiency was limited by optical losses at the front planar surface. As a consequence, we focus on the introduction of a texturized front surface to the device. Firstly, we characterize the contact formation by laser processing on texturized surfaces by SEM image showing that the size of the contacted region is difficult to determine. By measuring contact resistance and surface recombination velocity, we deduce that the laser process of such surfaces leads to a contacted region which is smaller than the one where passivation is lost. The obtained information is included in 3D simulations to get the optimum size of the contacts, i.e. optimum laser power. Additionally, a new front grid metallization is introduced in order to reduce shadowing. Due to the rear emitter configuration of these devices, front surface recombination is crucial for collecting photogenerated carriers. Thus, optimum laser power is very close to the minimum to obtain a reliable contact. Finally, 2x2 cm 2 solar cells are fabricated with a best efficiency of 17.0 %., Peer Reviewed, Postprint (published version)

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Cu2 ZnSn(S1-ySey )4 (CZTS) thin-film solar cells have been qualified as potential competitors of the more established CIGS ones. One of the more important handicaps of CZTS solar cells is the open-circuit voltage deficit. The rear-contact/absorber interface is known to be very sensitive to the formation of secondary phases, which are detrimental for the electrical behavior of photovoltaic devices. The addition of intermediate layers to favor the formation of an adequate interface has been repeatedly tested. In this work, an amorphous silicon carbide (a-SiC) layer is added to explore its influence on the material properties and electrical performance of CZTSe solar cells. According to scanning electron microscopy (SEM) analysis, when the a-SiC layer thickness is increased, bigger grains along the absorber are obtained. Additionally, a lower [VCu + ZnCu ] defect cluster density is also deduced from the analysis of Raman measurements. Both results indicate a favorable impact of a-SiC films on the material quality of the absorber. Fabricated solar cells show an enhancement of 0.9% abs. of efficiency compared to identical solar cells without a-SiC layers used as a reference. This increase is mainly related to an improvement of open-circuit voltage and fill factor (FF) when the proposed intermediate layer is included., Peer Reviewed, Postprint (author's final draft)

In order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them, Postprint (author's final draft)

© 2016 Elsevier B.V. All rights reserved. This paper introduces the possibility to produce 1-2 cm2 and tens of layers colloidal crystals on different non-flat surfaces by means of electrospray deposition. Two different types of crystalline silicon surfaces were tested: nanostructured, Postprint (author's final draft)

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p+ emitters are based on laser processed aluminum oxide/silicon carbide (Al2O3/SiCx) films. The p+ emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p+ regions with a surface charge induced emitter in between based on the high negative charge located at the Al2O3/c-Si interface. These emitters are fabricated at low temperature (< 400 °C) and could be directly compared to silicon heterojunction emitters with the advantage that the deposition of a Transparent Conductive Oxide (TCO) film can be avoided, since they are based on p+/n c-Si homojunctions. Additionally, the involved films are transparent to the IR photons ( >1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p+ regions or pitch ranging from 200 to 350 µm with a front surface based on silicon heterojunction technology. Best efficiency (18.1%) is obtained for a pitch of 250 µm as a consequence of the trade-off between Voc and FF values., Peer Reviewed, Postprint (published version)

In crystalline silicon (c-Si) solar cell field, an intensive effort is being paid to reduce the quantity of silicon material used in each cell in order to minimize its costs. With the reduction of wafer thickness, light trapping inside the c-Si absorber becomes more and more necessary. Several photonic structures have been proposed underlining their optical properties. However, addressing other technological issues, like contact formation through the photonic structure, is also necessary for their application into finished devices. In this paper we study the viability of laser firing technique to create solar cell base contacts through inverse opals deposited on the previously passivated rear surface of the device as photonic light trapping structures. Firstly, we check out that electrical surface passivation properties are not degraded during the inverse opals fabrication steps. Next, from SEM images we deduce that the inverse opal is mechanically and thermally stable after laser processing. Moreover, reflectance measurements show that optical properties are also maintained. From these results, we can conclude that inverse opal fabrication is compatible with solar cell technology and that contacts can be created by laser means without damaging the surrounding 3D inverse opal structure neither the silicon below it., Peer Reviewed, Postprint (author’s final draft)

Electrospray technique has been used in previous works as an excellent way to develop ordered nanostructures. This work focuses on the necessary conditions to achieve 3D nano-ordered layers, which are mainly determined by the conductivity of the liquid where nanoparticles are solved and the existence of an electrical field gradient. Changes in the conductivity induce a different evaporation rate during the ejection phase and control the amount of liquid that is deposited on the substrate. Controlling the conductivity, the electrical field and the quantity of liquid on the substrate different nanostructures can be fabricated, ranging from a semicovered monolayer of scattered nanoparticles up to a fully 3D colloidal crystal., Postprint (published version)

Postprint (published version)

In this paper we introduce the electrospray technique as a suitable method to create SiO2 3D ordered nanostructures. We describe the experimental procedure and deposition parameters required. We have found that the use of a high electric field is mandatory to, first, induce the Taylor cone and then, to get 3D order while the nanospheres assemble in the substrate in the drying phase. (C) 2014 Elsevier B.V. All rights reserved., Postprint (published version)

An electrospray technique has been used to deposit SiO2 nanoparticles as insulator layer of a metal-insulator-metal device. Impedance spectroscopy measurements show that a 4.4 factor increase in capacitance is achieved compared to a continuous dielectric layer of the same permittivity and dimensions., Peer Reviewed, Postprint (published version)

This paper shows an innovative and low temperature fabrication technology for crystalline silicon (c-Si) solar cells where the highly-doped regions are punctually defined through laser processed dielectric films. Phosphorus-doped silicon carbide stacks (SiCx(n)) and aluminium oxide/silicon carbide (Al2O3/SiCx) stacks are used for the creation of n+ and p+ regions respectively. These films provide excellent surface passivation on both n- and p-type substrates with effective surface recombination velocity below 20 cm/s. Moreover, a wide laser parameter window for laser processing them leads to low recombination highly-doped regions that show emitter saturation current densities of 21 and 113 fA/cm2 for n+ and p+ emitters respectively. All this is combined in the DopLa (Doped by Laser) cell structure whose fabrication process can be reduced to wafer cleaning, film depositions, laser processing and metallization. As a proof of concept, 1x1 cm2 solar cells were finished on both p- and n-type substrates with promising results. The analysis of loss mechanisms shows that optical losses and technological issues in the translation of surface passivation from the solar cell precursors to the final device are limiting efficiency. Both are not inherent to DopLa structure and suggest room for improvement in these devices. On the other hand, the crucial role played by ohmic losses in the proposed structure is identified. These ohmic losses arise from the fact that both base contacts and emitter regions are defined in point-like patterns. Firstly, base contacts are defined in a 1 mm pitch square matrix introducing additional series resistance that can be reduced by using low resistivity substrates. Secondly, the emitter consists of laser processed local diffusions with an inversion layer emitter in-between characterized by very high sheet resistances. The ohmic losses introduced by this induced emitter are closely linked to the fixed charge density located at the dielectric/c-Si in, Peer Reviewed, Postprint (published version)

Postprint (published version)

Most of the high-efficiency c-Si solar cells are based on dielectric films that electrically passivate c-Si surface and must keep their passivation properties after metal deposition on top of them. This work studies the impact of three different aluminum Physical Vapor Deposition (PVD) methods (thermal, e-beam, sputtering) on the c-Si surface passivation provided by SiO2 and Al2O3 films. Effective surface recombination velocity is measured before and after metal deposition. Results show that e-beam and sputtering techniques degrade surface passivation while thermal evaporation has no impact. Surface passivation can be recovered and even improved by means of an annealing with the aluminum film on top of the dielectric leading to the so-called alnealing. Additionally, after this alnealing Capacitance-Voltage measurements and lifetime spectroscopy analysis suggest a strong dependence of fixed charge density for SiO2 films on the metal deposition technique that helps in c-Si surface passivation., Peer Reviewed, Postprint (published version)

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Layers of AlN and CNx were investigated as suitable films to coat thin film anemometers because they are simultaneously electrical isolators and thermal conductors. Thermal time constants were measured and thermal equivalent models are proposed in this work. AlN performed better in the experiments., Peer Reviewed, Preprint

Nanostructuring materials such as silicon provides a good technology to fabricate optical and sensing devices. The possibility to fill the pores or channels with different material opens the way to new applications. In this work, we study the electrokinetics of electrospraying technique to fill porous material with nanobeads. The simulations take into account a photonic crystal topology applying a difference potential of 14 kV. Measurements show the viability of filling alumina nanoporous with 360nm polyestyrene nanospheres., Postprint (published version)

Diseño y posterior estudio de distintos dispositivos basados en CdSe QDs, [ANGLÈS] Throughout this project it is intended to study the electrical properties of Quantum Dots, semiconductor nanoparticles, by manufacturing various kinds of solar cells and to analyze their characteristics. Each new device is an immediate evolution of the above, to be able to analyze the contribution of each innovation separately. To carry out this task will require a study of the current state of technology as well as the properties and peculiarities of each material. It will also be essential to learn how to operate the different instruments used for the fabrication and characterization of the devices, and the various methodologies used in each environment., [CASTELLÀ] A lo largo de este proyecto se pretende estudiar las características eléctricas de los Quantum Dots, unas nanopartículas semiconductoras, mediante la fabricación de distintos tipos de células solares, así como analizar las características de éstas. Cada nuevo dispositivo supone una evolución inmediata del anterior, de manera que se podrá analizar la aportación de cada innovación de forma separada. Para llevar a cabo esta tarea, será necesario realizar un estudio del estado actual de esta tecnología, así como de las propiedades y singularidades de cada material. También será fundamental aprender el funcionamiento de los distintos instrumentos empleados para la fabricación y caracterización de los dispositivos, además de las distintas metodologías de trabajo empleadas en cada entorno., [CATALÀ] Durant la realització d'aquest projecte es pretén estudiar les característiques elèctriques dels Quantum Dots, unes nanopartícules semiconductores, mitjançant la fabricació de diferents tipus de cèl·lules solars, així com analitzar les seves característiques. Cada nou dispositiu suposa una evolució immediata de l'anterior, de manera que es podrà analitzar l'aportació de cada innovació de forma separada. Per dur a terme aquesta tasca, serà necessari realitzar un estudi de l'estat actual d'aquesta tecnologia així com de les propietats i singularitats de cada material. També serà fonamental aprendre el funcionament dels diferents instruments emprats per a la fabricació i caracterització dels dispositius, a més de les diferents metodologies de treball emprades en cada entorn.

Preprint

Català: L'estudi realitzat en aquest projecte pretén experimentar amb l'ús de quantum dots, nanopartícules semiconductores, en la fabricació de dispositius electrònics. Al analitzar els camps i les aplicacions en les que aquestes nanopartícules s'utilitzen, s'observa que els estudis sobre la seva part elèctrica son molt més escassos que els que tracten sobre la seva part òptica. Per estudiar aquesta part elèctrica es proposa una estructura formada per ITO, quantum dots i alumini, sobre una oblia de borosilicat, que es fabrica, es caracteritza i s'analitza. Per poder realitzar tota aquesta feina, es necessari l'aprenentatge de tots aquells equips i instruments que forment part del procés i de la metodologia de treball d'una sala blanca. A més, abans de començar amb la fabricació del dispositiu final, s'han de realitzar múltiples experiments i proves per assegurar que totes les parts d'aquest procés són adequades., Castellano: El estudio realizado en este proyecto pretende experimentar con el uso de quantum dots, nanopartículas semiconductoras, en la fabricación de dispositivos electrónicos. Al analizar los campos y aplicaciones en las que estas nanopartículas se utilizan, se observa que los estudios sobre su parte eléctrica son mucho más escasos que los que tratan sobre su parte óptica. Para estudiar esta parte eléctrica se propone una estructura formada por ITO, quantum dots y aluminio, sobre una oblea de boro-silicato, que se fabrica, se caracteriza y se analiza. Para poder llevar a cabo todo este trabajo, es necesario el aprendizaje de todos aquellos equipos e instrumentos que forman parte del proceso y de la metodología de trabajo de una sala blanca. Además, antes de empezar con la fabricación del dispositivo final, se deben realizar múltiples experimentos y pruebas para asegurar que todas las partes de dicho proceso son adecuadas., English: The aim of this project is to experiment with the use of quantum dots, semiconductor nanoparticles, in the manufacture of electronic devices. Analyzing the fields and applications in which these nanoparticles are used, it is noted that there are fewer studies about their electric part than about their optical part. In order to study this electric part, a structure of ITO, quantum dots and aluminium, on a borosilicate wafer is proposed. This structure is manufactured, characterized and finally analyzed. To carry out all this work, it is necessary to learn how to use all the equipment and instruments that are part of this process and the methodology of work in a clean room. Moreover, before starting with the final device fabrication, the necessary experiments and tests should be done to ensure that all the parts of this process are adequate.

Nowadays the nanotechnology is pushing hard in almost every direction of the technology. Creating patterns with nanoparticles would be a very useful technique in order to manipulated nanoparticles. Here comes the motivation for this project, the possibility to get a faster an easier way to create layers and patterns using the electrospray technique. The main aim for this project is the construction of an electrospray system for nanoparticles deposition and the characterization of the nanoparticle layers deposited with this system. The necessary equipment to build the electrospray setup is explained and the gold and polystyrene nanoparticles from 100 to 630nm are described. This particles and all the experiments have been characterized with an electronic microscope (SEM-FIB) equipped with and x-ray EDS system from the CRNE. And nally a complete description of the experiments and the layers created with the di erent variations of the electrospray setups.

In this work we want to explore some techniques, microfluidic and electrosprayionization based, suitable for dynamic microarrays' fabrication. The fabrication techniques are based on manipulation and self-assembly of selective coated micro and nanobeads. The simulation will include electro-osmotic flow, species transport, and electrostatics., Peer Reviewed, Postprint (published version)

Photonic crystals are widely used in optical applications as waveguides and band filters. Filling the periodic structural material of photonic crystals with other materials is very useful in order to change the optical properties of the devices. In this paper electrostatic COMSOL simulations describing an electrospray deposition of particles in macroporous structures are performed., Peer Reviewed, Postprint (published version)