Publications

2017

• Silicon surface passivation properties of aluminum oxide grown by atomic layer deposition for low temperature solar cells processes
  
  • Lebreton Fabien
  , 2017. This thesis focuses on the passivation properties provided by thin Al2O3 films grown by atomic layer deposition (ALD) from TMA and H2O for silicon solar cells having process temperatures lower than 400 °C. The first part of this doctoral work aims at identifying the formation mechanisms of negative electrostatic charges in aluminium oxide. Thus, the effects of post-deposition illumination (namely photon flux and photon energy), as well as substrate temperature were investigated. It was found that at least 70 % of what are generally named “fixed charges” are in fact trapped charges resulting from the injection of carriers from the silicon substrate into the aluminium oxide. From this result, we studied the influence of Al2O3 deposition parameters and post-deposition treatments on charge trapping and resulting passivation performances within an Al2O3/a-SiNX:H stack on p-type c-Si. The dependence of passivation performance (and stability) on Al2O3 thickness has been highlighted. Best compromise has been found to be around 60 ALD cycles (~6 nm), providing a lifetime up to 4500 µs. The second part of this PhD deals with the degradation mechanisms of passivation. Blistering at the c-Si/Al2O3 interface is the first studied degradation mechanism. Thanks to coloured picosecond acoustic microscopy, the Al2O3/c-Si adhesion has been confirmed to be reduced by Al2O3 thickening but also by the reduction of its deposition temperature, i.e. an increase of hydrogen content. A thermal drift during ALD (TD-ALD) has been used to solve this blistering issue. Gradual increase of the substrate temperature during the growth favours the release of hydrogen from the wafer/Al2O3 interface. For 60 ALD cycles, TD-ALD increased the lifetime up 5500 µs. Finally, the weakening of the electrostatic passivation arising from the positive charges in a-SiNX:H capping layer has been underlined by finite element simulations. The a-SiNX:H properties have been experimentally tuned thanks to a design of experiment approach. New a-SiNX:H capping containing 50 % less positive fixed charges resulted in a lifetime of 8800 µs for 60 TD-ALD cycles, i.e. an outstanding surface recombination velocity of 0.8 cm.s-1.
• Fabrication of hierarchical hybrid nanostructured electrodes based on nanoparticles decorated carbon nanotubes for Li-Ion batteries
  
  • Ezzedine Mariam
  , 2017. This thesis is devoted to the bottom-up fabrication of hierarchical hybrid nanostructured materials based on active vertically aligned carbon nanotubes (VACNTs) decorated with nanoparticles (NPs). Owing to their unique structure and electronic properties, VACNTs act as a support matrix and an excellent current collector, and thus enhance the electronic and ionic transport pathways. The nanostructuration and the confinement of sulfur (S) in a conductive host material improve its conductivity, while the nanostructuration of silicon (Si) accommodates better the volume change during the electrochemical reactions. In the first part of the thesis, we have synthesized VACNTs by a hot filament chemical vapor deposition (HF-CVD) method directly over aluminum and copper commercial foils without any pretreatment of the substrates. In the second part, we have decorated the sidewalls and the surface of the VACNT carpets with various LIB's active electrode materials, including S and Si NPs. We have also deposited and characterized nickel (Ni) NPs on CNTs as alternative materials for the cathode electrode. No conductive additives or any polymer binder have been added to the electrode composition. The CNTs decoration has been done systematically through two different methods: wet method by electrodeposition and dry method by physical vapor deposition (PVD). The obtained hybrid structures have been electrochemically tested separately in a coin cell against a lithium counter-electrode. Regarding the S evaporationon VACNTs, and the S@VACNTs structure, these topics are investigated for the first time to the best of our knowledge.Preliminary tests on the obtained nanostructured cathodes (S@VACNTs coated with alumina or polyaniline) have shown that it is possible to attain a specific capacity close to S theoretical storage capacity. The surface capacity of S@VACNTs, with 0.76 mg cm-2 of S, at C/20 rate reaches 1.15 mAh cm-2 at the first cycle. For the nanostructured anodes Si@VACNTs, with 4.11 mg cm-2 of Si showed an excellent surface capacity of 12.6 mAh cm-2, the highest value for nanostructured silicon anodes obtained so far. In the last part of the thesis, the fabricated nanostructured electrodes have been assembled in a full battery (Li2S/Si) and its electrochemical performances experimentally tested. The high and well-balanced surface capacities obtained for S and Si nanostructured electrodes pave the way for realization of high energy density, all-nanostructured LIBs and demonstrate the large potentialities of the proposed hierarchical hybrid nanostructures' concept.
• Modèles de prévision de la production d’électricité d’origine photovoltaïque : où sont les facteurs d’incertitude ?
  
  • Migan-Dubois Anne
  • Calderón Obaldía Fausto
  • Badosa Jordi
  • Bourdin Vincent
  • Bonnassieux Yvan
  , 2017.
• Photovoltaic characterization under real condition
  
  • Migan-Dubois Anne
  • Badosa Jordi
  • Calderón Obaldía Fausto
  • Abdel Nour Christine
  • Bourdin Vincent
  • Bonnassieux Yvan
  , 2017.
• Comprehensive analyses of core–shell InGaN/GaN single nanowire photodiodes
  
  • Zhang H.
  • Guan N
  • Piazza V
  • Kapoor A
  • Bougerol C.
  • Julien J
  • Babichev a V
  • Cavassilas C
  • Bescond M.
  • Michelini M
  • Foldyna M.
  • Gautier E.
  • Durand Christophe
  • Eymery J.
  • Tchernycheva M.
  Journal of Physics D: Applied Physics, IOP Publishing, 2017, 50 (48), pp.484001. (10.1088/1361-6463/aa935d)
  DOI : 10.1088/1361-6463/aa935d
• Single wall carbon nanotube growth from bimetallic nanoparticles : a parametric study of the synthesis up to potential application in nano-electronics.
  
  • Forel Salomé
  , 2017. This manuscript presents an experimental study around the single wall carbon nanotubes (SWCNT) synthesis and their possible integration in nanodevices. The unique electronic and optical properties of carbon nanotubes make them a choice material for various applications, particularly in nano-electronics.Nevertheless, their integration in effective devices is still a challenge. This is mainly due to the difficulty to obtain large quantity of SWCNT with uniform properties, defined by their structure (i.e. chiral angle and diameter). Therefore, structure controlled growth of SWCNTs is a key point for progress in this field.Here, we established a new synthesis approach based on coordination chemistry and hot-filament chemical vapor deposition. This approach allows the design of various bimetallic catalyst nanoparticles for the SWCNT growth. As the synthesis process is generic, parametric study can be performed in order to better understand the influence of the various parameters on the structure of the as-grown SWCNTs. In particular, we will discuss the role of the growth temperature and the chemical composition of the catalyst on the final SWCNTs structure. The obtained SWCNTs are mainly characterized by Raman spectroscopy and electronic microscopy.In order to validate the observations performed by Raman measurement, the synthesized SWCNTs have been also integrated in field effect transistors (FET) devices. An analysis of the performance of the FET-device as a function of the SWCNTs used in its channel will be presented.Finally, SWCNTs integrated in these transistors have been functionalized with an inorganic chromophore of ruthenium.We demonstrate that the functionalization of the SWCNTs leads to a three order of magnitude reversible switch of the device conductivity triggered by visible light.
• Carbon nanotube sensor array for water monitoring with conjugated polymers
  
  • Lebental Bérengère
  • Benda Robert
  • Bodelot Laurence
  • Florea Ileana
  • Godumala Mallesham
  • Gusarov Boris
  • Gutierrez Alfredo
  • Loisel Loic
  • Merliot Erick
  • Ramachandran Sasikumar
  • Zhang Xin Yang
  • Zucchi Gaël
  , 2017, pp.18p. In the field of water quality monitoring, there is an increasing demand for compact, low cost multiparameter water monitoring probes. The goal of the H2020 Proteus project (www.proteus-sensor.eu) is to meet this demand: based on the use of a set of novel conjugated polymers (FR1753131) functionalizing non-covalently multi-walled carbon nanotubes, we herein demonstrate the simultaneous monitoring of pH, chlorine, chloride and calcium ions with a single heavily minaturized sensor chip. The principle of sensing is based on the resistance variations of the functionnalized carbon nanotube network (deposited by ink-jet printing) upon changing chemical concentrations in water. In this paper, we present the functionalization strategy, from polymer design to proof of CNT functionnalization to CNT-polymer interaction modeling. Then we show the fabrication process and study the sensor array response, both in the lab and along field deployments. The measurements clearly show selectivity between the different CNT-polymers sensors, for instance pH sensitivity enhancement by a factor of 10 compared with the other devices with one of our polymers tuned with a urea-derivative. For field testing, the sensor chips are integrated into a 250cm3 pre-industrial sensor nodes and tested for several weeks in Sense-City 40m water loop. We demonstrate the first scale one deployment of arrayed carbon nanotubes chemical sensors, for instance showing demonstrating the capability to monitor active chlorine (HClO) or pH in real time in the field.
• SnO2 nanoparticles as catalyst precursors for plasma-assisted VLS growth with controlled surface density
  
  • Dai Letian
  • Al-Ghzaiwat Mutaz
  • Chen Wanghua
  • Foldyna Martin
  • Maurin Isabelle
  • Alvarez J
  • Kleider Jean-Paul
  • Maurice Jean-Luc
  • Gacoin Thierry
  • Cabarrocas Pere Roca I.
  , 2017.
• Comparaison de modèles de complexité croissante pour la simulation de la température de modules photovoltaïques
  
  • Bourdin Vincent
  • Badosa Jordi
  • Calderón Obaldía Fausto
  • Abdel Nour Christine
  • Migan-Dubois Anne
  • Bonnassieux Yvan
  , 2017.
• Modèles de prévision de la production d’électricité d’origine photovoltaïque : où sont les facteurs d’incertitude ?
  
  • Migan-Dubois Anne
  • Calderón Obaldía Fausto
  • Badosa Jordi
  • Bourdin Vincent
  • Bonnassieux Yvan
  , 2017.
• In-situ investigation of local motion mechanisms in carbon nanotubes strain sensors
  
  • Bodelot Laurence
  • Charliac Jérôme
  • Hallais Simon
  • Lebental Bérengère
  • Pavic Luka
  • Tanguy Alexandre
  , 2017, pp.26p. In this work, we focus on percolating carbon nanotubes (CNT) networks deposited by inkjet printing on ethylene tetrafluoroethylene (EFTE) substrates. It was demonstrated that such devices constitute highly reproducible flexible strain sensors, whose resistance grows linearly with a gage factor close to 1 up to 600 µµ [1]. In the prospect of developing a physically-based model describing the resistance variation of these sensors under strain, the local motion mechanisms arising at the CNT network scale need to be understood. To this end, a setup was developed in order to observe CNT networks deposited on ETFE substrates submitted to tensile strains inside a scanning electron microscope (SEM). SEM images of CNT networks are thus obtained at different strain levels and processed by digital image correlation. This gives access to the strain fields developing at the scale of CNT networks and highlights local motion mechanisms arising within such networks when strained.
• Modeling and characterization of materials and nanostructures for photovoltaic application
  
  • Mrazkova Zuzana
  , 2017. Research in photovoltaics aims at lowering the price per watt of generated electrical power. Substantial efforts aim at searching for new materials and designs which can push the limits of existing solar cells. The recent development of complex materials and nanostructures for solar cells requires more effort to be put into their characterization and modeling. This thesis focuses on optical characterization, modeling, and design optimization of advanced solar cell architectures.Optical measurements are used for fast and non-destructive characterization of textured samples for photovoltaic applications. Surface textures enhance light-trapping and are thus desired to improve the solar cell performance. On the other hand, these textures make optical characterization more challenging and more effort is required for both, the optical measurement itself and subsequent modeling and interpretation of obtained data. In this work, we demonstrate that we are able to use optical methods to study the widely used pyramidal textures as well as very challenging randomly oriented silicon nanowire arrays.At first, we focused on the optical study of various pyramidal surfaces and their impact on the silicon heterojunction solar cell performance. We have found that vertex angles of pyramids prepared using various texturing conditions vary from the theoretical value of 70.52° expected from crystalline silicon. This change of the vertex angle is explained by regular monoatomic terraces, which are present on pyramid facets and are observed by atomic resolution transmission electron microscopy. The impact of a vertex angle variation on the thicknesses of deposited thin films is studied and the consequences for resulting solar cell efficiency are discussed. A developed optical model for calculation of the reflectance and absorptance of thin film multi-layers on pyramidal surfaces enabled a solar cell design optimization, with respect to a given pyramid vertex angle.In-situ Mueller matrix ellipsometry has been applied for monitoring the silicon nanowire growth process by plasma-enhanced vapor-liquid-solid method. We have developed an easy-to-use optical model, which is to our knowledge a first model fitting the experimental ellipsometric data for process control of plasma-assisted vapor-liquid-solid grown nanowires. The observed linear dependence of the silicon material deposition on the deposition time enables us to trace the fabrication process in-situ and to control material quality.
• Study of the U-Am-O ternary phase diagram
  
  • Epifano Enrica
  , 2017. Americium isotopes are the main contributors to the long-term radiotoxicity of the nuclear wastes, after the plutonium extraction. Among the reprocessing scenarios, the transmutation in fast neutron reactors using uranium-americium mixed oxide (U,Am)O2±x pellets seems promising. In this frame, the knowledge of the thermodynamics of the U-Am-O ternary system is of essential for the prediction of the behavior of (U,Am)O2 pellets and their possible interaction with the cladding, under normal and accidental conditions. This thesis is dedicated to the experimental investigation of U-Am mixed oxides on a wide range of Am contents (7.5 at.% ≤ Am/(Am+U) ≤ 70 at.%), with the aim to collect data for developing a thermodynamic model based on the semi-empirical CALPHAD method. The obtained results can be classified in three categories: structural, phase diagram and thermodynamic data. For the thermodynamic modeling of the ternary system, the assessment of the binary sub-systems is first required. As open questions still existed on the Am-O system, a first part of the work was dedicated to the study of the Am-O phase diagram by high-temperature (HT) XRD. The existence of a composition range of the bcc AmO1.61 phase was highlighted and the miscibility gap in the fluorite phase, proposed in the literature, was not found. Thanks to the new experimental data, the existing CALPHAD model of Gotcu et al. was modified. In a second step, structural investigations were performed on synthesized (U,Am)O2±x dioxides by coupling XRD, XAS and Raman spectroscopy. For all the compositions, the XRD confirmed the formation of a single fluorite structure. The O/M ratio (with M=U+Am) at room temperature was determined to be lower than 2; the stability of trivalent americium Am3+ in the dioxide solid solution was highlighted, which induces a partial oxidation of uranium from U4+ to U5+. This charge distribution, peculiar for a dioxide, is accompanied by the formation of complex oxygen defects in the fluorite structure. By a HT-XRD investigation of the mixed oxides under air combined with XAS characterization of the oxidized samples, it was shown that the presence of Am3+ leads to a stabilization of the dioxide fluorite phase toward the formation of oxides richer in oxygen, in comparison to the U-O system. New phase diagram data were obtained in the oxygen rich region at 1470 K: tie-lines in the M4O9-M3O8 and MO2+x-M3O8 domains were determined and the solubility of americium in the M4O9 and M3O8 oxides was estimated. The investigation of the U-Am-O phase diagram continued at higher temperature with the study of the solidus/liquidus transitions using a laser-heating technique, under argon and air, and post-melting characterizations conducted by SEM and XAS. The melting temperature of Am-U dioxides decreases with the increase of both the Am/(Am+U) and O/M ratios. Finally, thermodynamic properties of the U1-yAmyO2±x oxides were measured: enthalpy increments using drop calorimetry, partial vapor pressures by Knudsen cell effusion mass spectrometry (KEMS). An excess contribution to the heat capacity at high temperature was observed and this was attributed to the reduction of the dioxides at high temperature (formation of oxygen vacancies). The KEMS results lead to determine the congruent vaporization composition at 2300 K, for a Am/(Am+U) ratio of 0.6 and an O/M ratio lower than 1.9. Finally, the CALPHAD thermodynamic assessment of the U-Am-O system was started, by focusing the attention on the modelling of the fluorite phase. A good agreement between the model and the oxygen potential data for (U0.5Am0.5O2±x) and the cation distribution was achieved. Furthermore, the model is able to satisfactorily reproduce the KEMS data and hence the equilibrium between the dioxide and gas phase. For the perspectives of this work, the optimization of the thermodynamic model should be extended to describe the phase equilibria involving the M4O9, M3O8 oxides and the liquid phase.
• In-situ Mueller matrix ellipsometry of silicon nanowires grown by plasma-enhanced vapor-liquid-solid method for radial junction solar cells
  
  • Mrazkova Z.
  • Foldyna M.
  • Misra S.
  • Al-Ghzaiwat M.
  • Postava K.
  • Pištora J.
  • Roca I Cabarrocas P.
  Applied Surface Science, Elsevier, 2017, 421, pp.667 - 673. (10.1016/j.apsusc.2016.12.199)
  DOI : 10.1016/j.apsusc.2016.12.199
• Surface Mechanisms on Dielectric Surfaces Exposed to Low Pressure Glow Discharge and Atmospheric Pressure Plasma Jets
  
  • Guaitella Olivier
  • Morillo-Candas Ana-Sofia
  • Slikboer Elmar
  • Hofmans Marlous
  • Sobota Ana
  • Klarenaar Bart
  • Engeln Richard
  • Garcia-Caurel Enric
  • Guerra V.
  • Marinov Daniil
  , 2017.
• Comparison of FTPS performed on thin films and solar cells
  
  • Puspitosari Nastiti
  • Longeaud Christophe
  • Lachaume Raphaël
  • Zeyu Li
  • Rusli Rusli
  • Cabarrocas Pere Roca I.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2017, 14 (10), pp.1700165. (10.1002/pssc.201700165)
  DOI : 10.1002/pssc.201700165
• Nanometer scale point contacting techniques for silicon Photovoltaic devices
  
  • Khoury Rasha
  , 2017. The use of point contacts has made the Passivated Emitter and Rear Cell design one of the most efficient monocrystalline-silicon photovoltaic cell designs in production. The main feature of such solar cell is that the rear surface is partially contacted by periodic openings in a dielectric film that provides surface passivation. However, a trade-off between ohmic losses and surface recombination is found. Due to the technology used to locally open the contacts in the passivation layer, the distance between neighboring contacts is on the order of hundreds of microns, introducing a significant series resistance.In this work, I explore the possibility and potential advantages of using nanoscale contact openings with a pitch between 300 nm to 10 µm. Analytic and numerical simulations done during the course of this thesis have shown that such nanoscale contacts would result in negligible ohmic losses while still keeping the surface recombination velocity Seff,rear at an acceptable level, as long as the recombination velocity at the contact (Scont) is in the range from 103-105 cm/s. To achieve such contacts in a potentially cost-reducing way, my experimental work has focused on the use of polystyrene nanospheres as a sacrificial mask.The thesis is therefore divided into three sections. The first section develops and explores processes to enable the formation of such contacts using various nanosphere dispersion, thin-film deposition, and layer etching processes. The second section describes a test device using a thin-film amorphous silicon NIP diode to explore the electrical properties of the point contacts. Finally, the third section considers the application of such point contacts on crystalline silicon by exploring localized doping through the nanoholes formed.In the first section, I have explored using polystyrene nanoparticles (NPs) as a patterning mask. The first two tested NPs deposition techniques (spray-coating, spin-coating) give poorly controlled distributions of nanospheres on the surface, but with very low values of coverage. The third tested NPs deposition technique (floating transfer technique) provided a closely-packed monolayer of NPs on the surface; this process was more repeatable but necessitated an additional O2 plasma step to reduce the coverage area of the sphere. This was performed using matrix distributed electron cyclotron resonance (MD-ECR) in order to etch the NPs by performing a detailed study.The NPs have been used in two ways; by using them as a direct deposition mask or by depositing a secondary etching mask layer on top of them.In the second section of this thesis, I have tested the nanoholes as electrical point-contacts in thin-film a-Si:H devices. For low-diffusion length technologies such as thin-film silicon, the distance between contacts must be in the order of few hundred nanometers. Using spin coated 100 nm NPs of polystyrene as a sacrificial deposition mask, I could form randomly spaced contacts with an average spacing of a few hundred nanometers. A set of NIP a-Si:H solar cells, using RF-PECVD, have been deposited on the back reflector substrates formed with metallic layers covered with dielectrics having nanoholes. Their electrical characteristics were compared to the same cells done with and without a complete dielectric layer. These structures allowed me to verify that good electrical contact through the nanoholes was possible, but no enhanced performance was observed.In the third section of this thesis, I investigate the use of such nanoholes in crystalline silicon technology by the formation of passivated contacts through the nanoholes. Boron doping by both thermal diffusion and ion implantation techniques were investigated. A thermally grown oxide layer with holes was used as the doping barrier. These samples were characterized, after removing the oxide layer, by secondary electron microscopy (SEM) and conductive probe atomic force microscopy (CP-AFM).
• Low-temperature deposition of transparent conductive layers for perovskite-silicon tandem cells
  
  • van Stappen Jonas
  • Dindault Chloé
  • Bourgeteau Tiphaine
  • Lee Heejae
  • Tondelier Denis
  • Geffroy Bernard
  • Bonnassieux Yvan
  , 2017. Since 2013, single-junction research-cell power conversion efficiencies of perovskite cells have risen by about 8%$_{abs}$ to 22.1%, while multicrystalline silicon and monocrystalline silicon efficiencies have risen by less than 2% abs and less than 1% abs , respectively Tandem cells with a perovskite top cell and a silicon bottom cell, recently achieving 23.6% in two-terminal configuration, present a promising alternative to further increase the relatively stagnant performance of already highly-optimized single-junction silicon cells. To facilitate such an advance, methods to deposit high-quality transparent conductors (TCs) which do not subject the perovskite layer to degradation during deposition need to be found. We utilize a spin-coating solution deposition process optimized for high reproducibility, yielding the single-junction MAPbl$_{3-x}$ Cl x perovskite cell stack shown in Figure 1, with an average efficiency of 7.94 $\pm$ 0.68 % with a non-transparent electrode. Two different TC electrodes are tested on these cells: evaporated thin-film semi-transparent Ag layers and low-temperature RF-sputtered indium tin oxide layers. For the latter, buffer layers of either thin-film Ag, Ag/BCP, Ag nanowires or interlinked PCBM are used to protect the organic layer stack from sputtering damage. By comparing transparency and efficiency, we will identify the most suitable approach
• Perovskites hybrides par évaporation pour des cellules solaires à hauts rendements
  
  • Dindault Chloé
  • Geffroy Bernard
  • Bonnassieux Yvan
  • Tondelier Denis
  , 2017. Depuis 2009, les matériaux perovskites de structure ABX 3 (où A est un cation organique, B un métal et X un halogène) attirent de plus en plus d'intérêt dans le domaine du photovoltaïque. En effet, en moins d'une décennie les rendements ont augmentés de 3.9 % à plus de 22 %, une progression qu'aucune autre technologie PV n'a jamais connue. Ces incroyables matériaux peuvent être obtenus par voie liquide (en une [3] ou deux [4] étapes(s)) ou par différentes techniques par voie sèche. En 2013, Snaith et al. [5] publient une étude comparative entre la voie liquide une étape et la co-évaporation en voie sèche. Pour un même matériau MAPbl$_{3-x]$ Cl$_x$ , les dispositifs à base de couches évaporées atteignent 15.4 % d'efficacité contre 8.6 % pour les dispositifs à base de dépôts en voie liquide. Si actuellement la grande majorité des travaux porte sur la voie liquide, les techniques par voie sèche apparaissent comme les plus adaptées à une future industrialisation des procédés. En effet, celles-ci permettent une meilleure homogénéité sur des larges surfaces. En partant de différents précurseurs tels que CH$_3$ NH$_3$I, CH(NH$_2$)$_2$I ou CH$_3$ NH$_3$ Br et Pbl$_2$ ou PbBr$_2$ , différents films de perovskites sont obtenus par co-évaporation. Ceux-ci sont ensuite intégrés dans des cellules solaires de structures variées.,
• Novel Concepts in the PECVD Deposition of Silicon Thin Films : from Plasma Chemistry to Photovoltaic Device Applications
  
  • Wang Junkang
  , 2017. This thesis describes the study of silicon thin film materials deposition and the resulting photovoltaic devices fabrication using different types of plasma-enhanced chemical vapour deposition (PECVD) techniques.In the first part, we combine a SiF4/H2 plasma chemistry with the matrix-distributed electron cyclotron resonance (MDECR) PECVD to obtain high growth rate microcrystalline silicon (µc-Si:H). Due to the special design of MDECR system, careful investigation of the impact energy of impinging ions to material deposition can be accessible. We find that moderate ion energy conditions is beneficial to achieve a significant drop in the density of nano-voids, thus a higher quality material with better stability can be obtained. A two-step deposition method is introduced as an alternative way to eliminate the existence of amorphous incubation layer during film growth.The second part of work is dedicate to the exploration of the Tailored Voltage Waveforms (TVWs) excitation technique for capacitively coupled plasmas (CCP) processes. As an advantage over the conventional sinusoidal excitations, TVWs technique provide an elegant solution for the ion flux-energy decoupling in CCP discharges through the electrical asymmetry effect, which makes the independent study of the impact of ion energy for material deposition at relatively high process pressure possible. Based on this insight, we have studied the deposition of µc-Si:H and amorphous silicon (a-Si:H) from the SiF4/H2/Ar and SiH4/H2 plasma chemistry, respectively. From the structural and electronic properties analysis, we find that the variation of ion energy can be directly translated into the material quality. We have further applied these results to photovoltaic applications and established bottom-up links from the controllable plasma parameters via TVWs to the deposited material properties, and eventually to the resulting device quality.In the last part, as a further application of TVWs, an “electrode-selective” effect has been discovered in the CCP processes. In the case of silicon thin film deposition from the SiF4/H2/Ar plasma chemistry, one can achieve a deposition process on one electrode, while at the same time either no deposition or an etching process on the counter electrode. This is due to two effects: the multi-precursor nature of the resulting surface process and the asymmetric plasma response through the utilization of TVWs. Moreover, such deposition/etching balance can be directly controlled through H2 flow rate. From a temporal asymmetry point of view, we have further studied the impact of process pressure and reactor geometry to the asymmetric plasma response for both the single-gas and multi-gas plasmas using the sawtooth waveforms. The product of pressure and inter-electrode distance P·di is deduced to be a crucial parameter in determine the plasma heating mode, so that a more flexible control over the discharge asymmetry as well as the relating “electrode-selective” surface process can be expected.
• New method for the growth of single-walled carbon nanotubes from bimetallic nanoalloy catalysts based on Prussian blue analog precursors
  
  • Castan Alice
  • Forel Salomé
  • Catala Laure
  • Florea Ileana
  • Fossard Frédéric
  • Bouanis Fatima
  • Andrieux-Ledier Amandine
  • Mazerat Stéphane
  • Mallah Talal
  • Huc Vincent
  • Loiseau Annick
  • Cojocaru Costel Sorin
  Carbon, Elsevier, 2017, 123, pp.583-592. Catalyst engineering is a key point for selective growth of single-walled carbon nanotubes (SWCNT) with chemical vapor deposition (CVD). Here, we develop a new general synthesis method able to produce a wide range of homogenous bimetallic catalyst nanoparticles with controlled stoichiometry and sizes. The basics of this catalyst synthesis is to use preformed stoichiometric bimetallic Prussian blue analog (PBA) nanoparticles. Catalyst nanoparticles are then prepared in-situ in a hot filament CVD reactor with subsequent high temperature treatment in reducing atmosphere prior to SWCNT growth. The capabilities of the synthesis route are demonstrated by testing five PBA systems involving various transition metals. Transmission electron microscopy (TEM), scanning TEM and energy dispersive X-ray spectroscopy (STEM-EDX), and in-situ X-ray photoelectron spectroscopy (XPS) measurements are used to finely follow the size and composition of the catalyst at each step of the process. Each system yields small size catalysts with a narrow distribution, which act as efficient catalysts for SWCNT growth with a good yield and small diameter distribution. The versatility of the PBA family paves a new way for a fine tuning of the catalyst properties monitored by the metal involved in the PBA, and for opening routes to more selective SWCNT synthesis. (10.1016/j.carbon.2017.07.058)
  DOI : 10.1016/j.carbon.2017.07.058
• Anharmonicity in Halide Perovskites for Photovoltaics
  
  • Marronnier Arthur
  • Lee Heejae
  • Geffroy Bernard
  • Even Jacky
  • Bonnassieux Yvan
  • Roma Guido
  , 2017.
• Colourless Self-Seeded Source for CPRI3 Mobile Fronthaul over 70 km Reach
  
  • Gay Mathilde
  • Hussain Kamal
  • Le Bouëtté Claude
  • Pamart Jean-Luc
  • Schoc Laurent
  • Aupetit-Berthelemot Christelle
  • Ao Li
  • Meghdadi Vahid
  • Brenot Romain
  • Maho Anaëlle
  • Chanclou Philippe
  • Barthomeuf Sylvain
  • Saliou Fabienne
  , 2018. We demonstrate field trial CPRI3 error-free transmission over field fibre at 2.5 Gbit/s with DWDM self-seeded RSOAs in the O-band. The use of FEC in transponders enables to achieve 30 dB optical budget and up to 70 km reach. (10.1109/ECOC.2017.8346180)
  DOI : 10.1109/ECOC.2017.8346180
• Physical modelling of bio sensors based on Organic Electrochemical Transistors
  
  • Shirinskaya Anna
  , 2017. Organic Electrochemical Transistors are widely used as transducers for sensors in bioelectronics devices. Although these devices have been extensively studied in the last years, there is a lack of fundamental understanding of their working mechanism, especially concerning the de-doping mechanism.This thesis is dedicated to Organic Electrochemical Transistors modelling. First of all, a numerical steady state model was established. This model allows implementing the Poisson-Boltzmann, Nernst-Planck and Nernst equations to describe the de-doping process in the conductive PEDOT:PSS layer, and ions and holes distribution in the device. Two numerical models were proposed. In the first, Local Neutrality model, the assumption of electrolyte ions trapping in PEDOT:PSS layer was taken into consideration, thus the local neutrality was preserved. In the second model the ions were allowed to move freely under applied electric field inside conductive polymer layer, thus only global electroneutrality was kept. It was experimentally proven that the Global Neutrality numerical model is valid to explain the global physics of the device, the origin and the result of the de-doping process. The transition from totally numerical model to analytical model was performed by fitting the parametric analytical Boltzmann logistic function to numerically calculated conductivity profiles. As a result, an analytical equation for the Drain current dependence on applied voltage was derived. By fitting this equation to experimentally measured Drain current- applied voltage profiles, we could obtain the maximum conductivity of a fully doped PEDOT:PSS layer. The maximum conductivity is shown to be dependent not only on the material, but also on device channel size. Using the maximum conductivity value together with the Conventional Semiconductor model it is possible to extract the other parameters for the full description of the OECT: intrinsic charge carrier density, initial holes density, initial PSS- concentration and conductive polymer layer volumetric capacitance. Having a tool to make easy parameters extraction and characterization of any OECT, permits not only to increase the level of device description, but most importantly to highlight the correlation between external and internal device parameters.Finally it is shown how to make the whole description of the real OECT device, all the models were validated by fitting the modeled and experimentally measured data profiles.As a result, not only the purely theoretical model was presented in this thesis to describe the device physics, but also the prominent step was made on simple real device characterization.
• Texturing optimization for bifacial n-PERT: are pyramids and/or black silicon the way to go for thinner devices?
  
  • Peyronnet Rafaël
  • Fischer Guillaume
  • Blévin Thomas
  • Johnson Erik
  • Drahi Etienne
  • Lemiti M
  Energy Procedia, Elsevier, 2017, 124, pp.250-259.