Publications

2019

• Doping of TiO2 nanotubes with nitrogen by annealing in ammonia for visible light activation: Influence of pre- and post-annealing in air
  
  • Bjelajac Andjelika
  • Petrović Rada
  • Popović Maja
  • Rakočević Zlatko
  • Socol Gabriel
  • Mihailescu Ion N.
  • Janaćković Djordje
  Thin Solid Films, Elsevier, 2019, 692, pp.137598. (10.1016/j.tsf.2019.137598)
  DOI : 10.1016/j.tsf.2019.137598
• Tunnel Oxide Modification During PECVD Poly-Si Deposition for Passivating Contacts
  
  • Desthieux Anatole
  • Posada Jorge
  • Grand Pierre-Philippe
  • Broussillou Cédric
  • Bazer-Bachi Barbara
  • Goaer Gilles
  • Messou Davina
  • Bouttemy Muriel
  • Drahi Etienne
  • Cabarrocas Pere Roca I
  , 2019.
• Local VOC Measurements by Kelvin Probe Force Microscopy Applied on P-I-N Radial Junction Si Nanowires
  
  • Marchat Clément
  • Dai Letian
  • Alvarez José
  • Le Gall Sylvain
  • Kleider Jean-Paul
  • Misra Soumyadeep
  • Roca I Cabarrocas Pere
  Nanoscale Research Letters, SpringerOpen, 2019, 14. This work focuses on the extraction of the open circuit voltage (VOC) on photovoltaic nanowires by surface photovoltage (SPV) based on Kelvin probe force microscopy (KPFM) measurements. In a first approach, P-I-N radial junction (RJ) silicon nanowire (SiNW) devices were investigated under illumination by KPFM and current-voltage (I-V) analysis. Within 5%, the extracted SPV correlates well with the VOC. In a second approach, local SPV measurements were applied on single isolated radial junction SiNWs pointing out shadowing effects from the AFM tip that can strongly impact the SPV assessment. Several strategies in terms of AFM tip shape and illumination orientation have been put in place to minimize this effect. Local SPV measurements on isolated radial junction SiNWs increase logarithmically with the illumination power and demonstrate a linear behavior with the VOC. The results show notably that contactless measurements of the VOC become feasible at the scale of single photovoltaic SiNW devices. (10.1186/s11671-019-3230-5)
  DOI : 10.1186/s11671-019-3230-5
• Synthesis and study of γ-Fe 2 O 3 and CoFe 2 O 4 based ferrofluids by means of spectroscopic Mueller matrix ellipsometry
  
  • Battie Yann
  • Stchakovsky Michel
  • Neveu Sophie
  • Jamon Damien
  • Garcia-Caurel Enric
  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics, AVS through the American Institute of Physics, 2019, 37 (6), pp.062929. Ferrofluids are colloidal suspensions generally composed of ferromagnetic or ferrimagnetic nanoparticles (NPs). In the present study, the authors have focused on the ellipsometric characterization of two types of ferrofluids: one constituting maghemite (γ-Fe2O3) NPs and the other cobalt ferrite (CoFe2O4) NPs. The optical properties of the NPs are extracted from the ellipsometric spectra by using the Maxwell–Garnett effective medium approximations. As expected, Mueller matrix measurements reveal that the ferrofluid becomes anisotropic under the influence of a magnetic field. The authors correlate this anisotropy to the preferential orientation of NPs along the magnetic field. (10.1116/1.5121286)
  DOI : 10.1116/1.5121286
• Experimental studies of the transmission of light through low-coverage regular or random arrays of silica micropillars supported by a glass substrate
  
  • Turbil Colette
  • Yoo Thomas Sang Hyuk
  • Simonsen Ingve
  • Teisseire Jeremie
  • Gozhyk Iryna
  • Garcia-Caurel Enrique
  Applied optics, Optical Society of America, 2019, 58 (33), pp.9267. (10.1364/AO.58.009267)
  DOI : 10.1364/AO.58.009267
• Radiative Recombination in Quadruple Cation Organic-Inorganic Mixed Halide Perovskite Layers: Electron Irradiation Induced Ageing Effects
  
  • Aversa Pierfrancesco
  • Öz Senol
  • Jung Eunhwan
  • Plantevin Olivier
  • Cavani Olivier
  • Ollier Nadège
  • Geffroy Bernard
  • Mathur Sanjay
  • Corbel Catherine
  , 2019.
• Annealing of Boron-Doped Hydrogenated Crystalline Silicon Grown at Low Temperature by PECVD
  
  • Chrostowski Marta
  • Alvarez J
  • Le Donne Alessia
  • Binetti Simona
  • Roca I Cabarrocas Pere
  Materials, MDPI, 2019, 12 (22), pp.3795. We investigate low-temperature (<200 • C) plasma-enhanced chemical vapor deposition (PECVD) for the formation of p-n junctions. Compared to the standard diffusion or implantation processes, silicon growth at low temperature by PECVD ensures a lower thermal budget and a better control of the doping profile. We previously demonstrated the successful growth of boron-doped epitaxial silicon layers (p+ epi-Si) at 180 • C. In this paper, we study the activation of boron during annealing via dark conductivity measurements of p+ epi-Si layers grown on silicon-on-insulator (SOI) substrates. Secondary Ion Mass Spectroscopy (SIMS) profiles of the samples, carried out to analyze the elemental composition of the p+ epi-Si layers, showed a high concentration of impurities. Finally, we have characterized the p+ epi-Si layers by low-temperature photoluminescence (PL). Results revealed the presence of a broad defect band around 0.9 eV. In addition, we observed an evolution of the PL spectrum of the sample annealed at 200 • C, suggesting that additional defects might appear upon annealing. (10.3390/ma12223795)
  DOI : 10.3390/ma12223795
• CARBON NANOTUBE-BASED FIELD-EFFECT TRANSISTOR FOR WATER QUALITY MONITORING
  
  • Zucchi Gaël
  • Cho Gookbin
  • Lebental Bérengère
  , 2019.
• SMART SYSTEM INTEGRATION OF A CHEMISTOR ARRAY BASED ON POLYMER-FUNCTIONALIZED-CARBON NANOTUBES ENABLES HIGHLY SELECTIVE WATER QUALITY MONITORING
  
  • Zucchi Gaël
  • Lebental Bérengère
  , 2019.
• CARBON NANOTUBE-BASED FIELD-EFFECT TRANSISTOR FOR WATER QUALITY MONITORING
  
  • Zucchi Gaël
  • Cho Gookbin
  • Lebental Bérengère
  , 2019.
• Multi-scale modelling of nano-sensors based on carbon nanotubes (cnts) and conjugated polymers for water quality monitoring
  
  • Benda Robert
  • Cancès Eric
  • Lebental Bérengère
  , 2019. We study resistive chemical sensors based on percolating networks of CNTs functionalized non-covalently by conjugated polymers. A change of resistance is expected in water upon complexation of a target ion by a specifically designed polymer probe. Multi-scale modelling aims at understanding and predicting the response of the sensor. First, we derive the functional dependence of the effective resistance of random percolating networks of stick nanowires on elementary physical parameters (nanowire linear resistance per unit length, nanowire/nanowire contact resistance, metallic electrode/nanowire contact resistance) [1]. This understanding of the three main contributions, of different physical origins, to the whole, experimentally measured sensor resistances, is useful for the design of optimal sensor dimensions and sensible element densities. Then, we study by means of variable-charge molecular dynamics, based on ReaxFF force field (within LAMMPS), the geometrical features of non-covalent functionalization of CNTs by conjugated polymers [2]. We benchmark the performance of ReaxFF force field for pi-pi stacking interacting compounds against other high-level electronic (DFT) methods, with a focus on the level of theory needed to model accurately London dispersion interactions (wave-function based theory vs. density functional theory) and to capture charge transfer from the organic molecule (or conjugated polymer) to the CNT -- this charge transfer is suspected to act as a doping and to modulate the sensor response. Finally, we study the complexation of target ions (e.g. chlorine, copper, calcium) by the polymer probes -- designed specifically for their affinity towards given ions -- by means of molecular dynamics simulations in solvent (water) with GROMOS classical force field, within GROMACS code. We test numerically the expected selectivity of the polymer probes to different ions, finding the possible binding sites and their corresponding binding energies. We confirm the binding energies obtained with this classical force field by ab-initio (DFT) calculations -- with CP2K code -- and derive association constants for the different ions and binding sites, with free energy calculation techniques using GROMACS.
• CARBON NANOTUBE-BASED SENSOR ARRAY FOR WATER CONTAMINANTS DETECTION
  
  • Zucchi Gaël
  • Azzouzi Sawsen
  • Lebental Bérengère
  , 2019.
• Development of in-situ photoluminescence characterization tools for the study of semiconductors for photovoltaics application
  
  • Sreng Mengkoing
  , 2019. During the last few decades, the conversion efficiency of photovoltaic solar cell has been significantly improved, almost reaching the Shockley-Queisser theoretical limit. At this point, a profound understanding of material properties and its evolution during the solar cell fabrication processes become increasingly crucial to further improve the cell conversion efficiency. For this reason, my doctoral studies have been focused on the development of in-situ characterization tools, which allows the studies of material properties in real time during the processes. The tools were developed based on photoluminescence techniques, in which the sample (semiconductor materials) is optically excited and simultaneously emits photons with energy approximately equal to the band gap of materials. In this thesis, three in-situ characterization tools will be presented.In-situ SSPL, based on steady-state photoluminescence technique, is developed to study the properties of semiconductor materials during the processes by directly measuring the steady-state PL intensity. After the upgrade of optical acquisition system, the tool has been used extensively to study the evolution of surface properties of crystalline silicon wafer, passivated by aluminum oxide (Al2O3) grown by atomic layer deposition (ALD) and hydrogenated amorphous silicon (a-Si:H) grown by plasma-enhanced chemical vapor deposition (PECVD), under Ar/H2 plasma exposure at different conditions. From these experiments, the behavioral differences between Al2O3-passivated sample and a-Si:H-passivated sample was observed and discussed. In addition, thanks to the plasma exposure experiment through a magnesium fluoride optical window (MgF2), the root cause of plasma-induced degradation of surface passivation was pin-pointed. Last but not least, the relationship between the dynamic of plasma-induced degradation and the plasma parameters (e.g. applied RF power, chamber pressure, and temperature) was also studied.To go one step further, in-situ MPL, based on modulated photoluminescence technique, is built to quantitatively study the properties of semiconductor materials. This characterization tool employs an intensity-modulated laser to excite the sample, so the minority carrier lifetime can be measured. After the conceptualization and fabrication of a new optical acquisition system, the system calibration and the optimization of MPL parameters were conducted. Furthermore, a characterization method was also developed, so the in-situ MPL is able to measure the minority carrier lifetime at a defined minority carrier density (e.g. 1015 cm-3 for non-concentrated single junction solar cell). After a lot of work, the tool is now fully functional and has been used to measure the minority carrier lifetime of crystalline silicon wafer during the de position of a-Si:H passivation layer, the thermal treatment, and the deposition of hydrogenated amorphous silicon nitride (a-SiNx:H) anti-reflection coating. The experimental results show that the temperature at which the processes were conducted plays a major role in activation and modification of surface passivation properties provided by Al2O3.Finally, as the tendency toward tandem solar cell has been continuously growing, another in-situ characterization tool, known as in-situ PLt (in-situ photoluminescence for tandem solar cell), was built. This characterization tool results from a combination of steady-state photoluminescence and modulated photoluminescence technique and was designed to study in real time the properties of both sub-cells independently and simultaneously. The in-situ PLt can be a potential characterization tool for the research toward high efficiency tandem solar cell.
• Naphthyl-fused phosphepines: Luminescent contorted polycyclic P-heterocycles
  
  • Delouche Thomas
  • Mokrai Réka
  • Roisnel Thierry
  • Tondelier Denis
  • Geffroy Bernard
  • Nyulászi László
  • Benkő Zoltán
  • Hissler Muriel
  • Bouit Pierre-Antoine
  , 2019. the article presents the synthesis of a new family of naphthyl-fused phosphepines through Ni-mediated CC coupling. Interestingly, the chloro-phosphine-oxide intermediate shows strong resistance toward oxidation/hydrolysis due to a combination of steric hindrance and pnictogen interactions. However it can undergo substitution reactions under specific conditions. The optical / redox properties and the electronic structure of these new $\pi$-systems were studied experimentally (UV-vis absorption, emission, cyclic voltammetry) and computationally (TD-DFT calculations, NICS investigation). Taking advantage of the luminescence of these derivatives, a blue emitting OLED has been prepared highlighting that these novel $\pi$-conjugated P-heterocycles appear as promising building blocks for solid-state lightning applications.
• Synthesis and Characterization of New n-type Materials for Electronic Applications
  
  • Yassar Abderrahim
  • Ren Shiwei
  , 2019.
• Study of the Molecular Bending in Azobenzene Self-Assembled Monolayers Observed by Tip-Enhanced Raman Spectroscopy in Scanning Tunneling Mode
  
  • Foti A.
  • Toccafondi C.
  • Ossikovski R.
  Journal of Physical Chemistry C, American Chemical Society, 2019, 123 (43), pp.26554-26563. Tip-enhanced Raman spectroscopy (TERS) is capable of amplifying the extremely weak Raman response of azobenzene self-assembled monolayers (SAMs), thus allowing for the chemical characterization of the sample surface at the nanoscale. Recently, we introduced a physical model describing the TERS intensity of azobenzene SAMs probed in a scanning tunneling mode configuration (STM-TERS) that takes into account the molecular bending induced by the high electric field inside the tunneling junction. The model predicts quite well the experimental variation in the TERS intensity of a hexyl azobenzene SAM (AzoC6) on gold polycrystalline film (111) by changing the electric field in the gap between the tip and the substrate. Nevertheless, a disagreement between the model and the experiment has been observed while studying, in the same conditions, the TERS intensity of undecyl azobenzene (AzoC11) SAM formed by molecules featuring an alkyl chain that is nearly two times longer with respect to the previous case. In this work, we extend the molecular bending model by considering an additional bending mechanism due to the mechanical interaction between the tip and the SAM, occurring when the tip-to-sample distance is shorter than the molecular length. The extended model is able to describe well the TERS intensity behavior by changing either the bias voltage or the tip-to-sample distance for both AzoC6 and AzoC11. Eventually, we determine quantitatively the difference in the elastic properties of the two molecules physically accounting for the difference in the TERS intensity behavior of the two SAMs. (10.1021/acs.jpcc.9b08299)
  DOI : 10.1021/acs.jpcc.9b08299
• Elaboration de films de perovskites hybrides par coévaporation pour des applications photovoltaïques.
  
  • Dindault Chloe
  , 2019. Hybrid perovskites celebrate this year their 10-year anniversary in the photovoltaic field. Besides the unprecedented rise in solar cells efficiencies, perovskite materials have tunable optical properties and can be manufactured at low cost, making them very promising candidates for the high efficiency, multijunction solar cells strategy. Perovskite crystal structure offers a relative degree of freedom, allowing the partial integration of multiple cations and halide ions. This chemical composition tuning translates into a bandgap tuning. Through fine chemical engineering, the 1.7 eV requirement for a c-Si-based tandem device can be achieved. Perovskite thin films can be prepared by a large variety of deposition techniques, from low cost precursors (CH3NH3I and PbI2 for instance), through low-temperature processes. While most of the reported works on perovskite thin films are based on the basic wet-process spincoating technique, this latter hardly allows large scale, homogeneous and reproducible deposition. With the future challenge of industrialization and the increasing interest for the Silicon/Perovskite tandem approach, solvent-free methods appear more suitable. Already widely implemented in the OLED industry, coevaporation stands as a viable option for perovskites’ future. Reported for the first time in 2013, coevaporated perovskites are still scarcely studied compared to wet-based techniques, requiring more expensive set ups. In the present thesis, we implemented and developed the coevaporation process to fabricate perovskite thin films for solar cells applications.Starting off on a proof-of-concept reactor to assess the feasibility of the technique, we got accustomed to the perovskite precursors behaviour and identify very early on the organic precursor to be hardly manageable, as reported in the literature. In six months, we were nonetheless able to obtain nice perovskite films leading to 9% efficient photovoltaic devices, unfortunately with a poor reproducibility that we think to be partially due to the cloud vapour behaviour of CH3NH3I. We eventually found ourselves missing some features on the equipment, preventing us from accurately get a grasp on the process. From this feedback we then designed, hand in hand with the manufacturer, a dedicated semi-industrial equipment for perovskite coevaporation. Following its implementation, we then focused on establishing the reproducibility of the method, trying to mitigate the parasitic effect of the organic compound. Even though the efficiencies in solar cells were still slightly lower for coevaporated perovskites, with respect to classical spincoated ones, we expected the material homogeneity to be in favour of the vacuum-based process. We then eventually integrated to this thesis a comparative study between wet- and dry-processed perovskite films using a Synchrotron-based X-ray spectromicroscopy technique.
• Energy Management for Microgrids: a Reinforcement Learning Approach
  
  • Levent Tanguy
  • Preux Philippe
  • Le Pennec Erwan
  • Badosa Jordi
  • Henri Gonzague
  • Bonnassieux Yvan
  , 2019, pp.1-5. This paper presents a framework based on reinforcement learning for energy management and economic dispatch of an islanded microgrid without any forecasting module. The architecture of the algorithm is divided in two parts: a learning phase trained by a reinforcement learning (RL) algorithm on a small dataset and the testing phase based on a decision tree induced from the trained RL. An advantage of this approach is to create an autonomous agent, able to react in real-time, considering only the past. This framework was tested on real data acquired at Ecole Polytechnique in France over a long period of time, with a large diversity in the type of days considered. It showed near optimal, efficient and stable results in each situation. (10.1109/ISGTEurope.2019.8905538)
  DOI : 10.1109/ISGTEurope.2019.8905538
• Silicon nanowire solar cells with μc-Si˸H absorbers for tandem radial junction devices
  
  • Dai Letian
  , 2019. In this thesis, we have fabricated silicon nanowire (SiNW) radial junction solar cells with hydrogenated microcrystalline silicon (μc-Si:H) as the absorber via low-temperature plasma-enhanced chemical vapor deposition (PECVD). To control the density of NW on the substrates, we have used commercially available tin dioxide (SnO₂) nanoparticles (NPs) with an average diameter of 55 nm as the precursor of Sn catalyst for the growth of SiNWs. The distribution of SnO₂ NPs on the substrate has been controlled by centrifugation and the dilution of the SnO₂ colloid, combined with the functionalization of the substrate. Subsequently, SnO₂ is reduced to metallic Sn after the H₂ plasma treatment, followed by the plasma-assisted vapor-liquid-solid (VLS) growth of SiNWs upon which the P, I and N layers constituting the radial junction solar cells are deposited. We have achieved a high yield growth of SiNWs up to 70% with a very wide range of NW density, from 10⁶ to 10⁹ /cm². As an additional approach of controlling the density of SiNWs we have used evaporated Sn as the precursor of Sn catalyst. We have studied the effect of the thickness of evaporated Sn, the effect of duration of H₂ plasma treatment and the effect of H₂ gas flow rate in the plasma, on the density of SiNWs.In-situ spectroscopic ellipsometry (SE) was used for monitoring the growth of SiNWs and the deposition of the layers of μc-Si:H on SiNWs. Combining in-situ SE and SEM results, a relationship between the intensity of SE signal and the length and the density of SiNWs during the growth was demonstrated, which allows to estimate the density and the length of SiNWs during the growth. We have carried out a systematic study of materials (intrinsic, p-type,n-type µc-Si:H and µcSiOx:H doped layers) and solar cells obtained in two plasma reactors named “PLASFIL” and “ARCAM”. The thicknesses of coating on the flat substrate and on the SiNWs have been determined with a linear relation which helps to design a conformal coating on SiNWs for each layer with an optimal thickness. The parameters of the SiNWs and the materials, affecting the performance of radial junction solar cells, have been systematically studied, the main ones being the length and the density of SiNWs, the thickness of intrinsic layer of μc-Si:H on SiNWs, the use of the hydrogenated microcrystalline silicon oxide (μc-SiOx:H) and the back reflector Ag. Finally, with the optimized silicon nanowire radial junction solar cells using the μc-Si:H as the absorber we have achieved an energy conversion efficiency of 4.13 % with Voc = 0.41 V, Jsc = 14.4 mA/cm² and FF = 69.7%. This performance is more than 40 % better than the previous published record efficiency of 2.9 %.
• Development of low-carbon footprint process for passivating contacts on p-type silicon wafers
  
  • Desthieux Anatole
  • Posada Jorge
  • Grand Pierre-Philippe
  • Broussillou Cédric
  • Bazer-Bachi Barbara
  • Goaer Gilles
  • Messou Davina
  • Bouttemy Muriel
  • Drahi Etienne
  • Cabarrocas Pere Roca I
  , 2019.
• Low Temperature p-n Junction Fabrication by PECVD for n-PERT Solar Cells: An Alternative to Boron Diffusion
  
  • Chrostowski Marta
  • Alvarez J
  • Kleider Jean-Paul
  • Kim K.-H.
  • Drahi Etienne
  • Roca I Cabarrocas Pere Roca I Cabarrocas
  , 2019.
• NANOFILAMENTS D'ALLIAGE DE GESN, PREPARATION ET APPLICATIONS
  
  • Roca I Cabarrocas Pere Roca I Cabarrocas
  • Chen Wanghua
  • Duguay Sébastien
  • Pareige Philippe
  • Azrak Edy
  , 2019.
• Luminescent hybrid materials for LED lighting
  
  • Lin Qiqiao
  , 2019. This thesis aimed at designing and synthesizing organic-inorganic hybrid materials with controlled luminescence and at investigating them as phosphors for LED lighting. The final goal was to obtain a white source of light. Indeed, commercial white LEDs are made up of a blue emitting device covered with a yellow phosphor. Combining these two colors yields white light. However, this light is not of good quality as it lacks some red component. This results in a bad rendering of the colors of objects illuminated by these sources of light. In our work, conjugated polymers with different emission colors have successfully been obtained. In particular, several single white emitters have been isolated.In this PhD thesis, not only the synthetic procedures and chemical characterizations are presented in detail, but also the studies of the photophysical properties of the polymers, either in solution or in the solid state. Solid state studies were performed on the bulk polymers and on the polymers dispersed into a polymeric matrix. These studies have lead to identify the limiting factors that could hamper the use of the materials. Solutions have been proposed to improve the materials performance and stability. Furthermore, 2,2’-bipyrimidine has been introduced as a new synthon for designing and developing conjugated polymers.
• Quantifying the mitochondrial content with diffusion MRI
  
  • Moutal Nicolas
  • Grebenkov Denis S
  • Clerjon Sylvie
  • Pagès Guilhem
  • Bonny J.-M.
  , 2019. The residual signal at high b-values in muscles is naturally explained by mitochondria. This work is a proof of concept and a prerequisite for developing in vivo methods to quantify the content of various organelles in muscle, e.g. for studying mitochondrial dysfunction in aging.
• Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates
  
  • Léon Cyril
  • Le Gall Sylvain
  • Gueunier-Farret Marie-Estelle
  • Kleider Jean-Paul
  • Roca I Cabarrocas Pere Roca I Cabarrocas
  , 2019.