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Accelerating Solar Cell Research Through Physics Modeling, Bayesian Machine Learning, and Automation
No full textInternational audienceThe race to develop more efficient and stable solar technologies demands advanced tools to unravel complex performance factors and degradation mechanisms. In this work, we present an integrated approach that combines physics-based modeling with Bayesian machine learning to gain deeper insights into photovoltaic performance and degradation. We show how this tool has been used to investigate the impact of various passivation layers in perovskite solar cells, revealing key efficiency factors that were experimentally validated through our collaboration with NTU via the SINERGIE French-Singaporean research network. Building on the findings of this study and other related work, we outline the development of our automated platform for the fabrication and characterization of next-generation solar cells. This platform will leverage the physics-informed Bayesian optimization tools we have developed to explore the parameter space more intelligently and efficiently, ultimately contributing to the creation of an international network of automated research platforms
Coupling strengthening with local stress relaxation in an 800 MPa yield strength strain transformable titanium alloy
No full textInternational audienceA novel strain transformable β-metastable titanium alloy, Ti–7.5Cr–1Sn–1Fe (TCSF), was designed using the "d-electron alloy design" method to achieve a unique balance of twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) deformation mechanisms. Tensile testing revealed excellent tensile properties, including a high yield strength ∼800 MPa, an ultimate tensile strength ∼1400 MPa, and exceptional strain-hardening over extended plastic deformation. Microstructural analysis revealed a high density of {332}〈113〉 deformation twins, with stress-induced α″ martensite forming at the twin/matrix interfaces, facilitating internal stress relaxation. This alloy exhibits a dynamic composite effect, driven by hierarchical deformation twin networks obstructing dislocation motion, enhancing strain hardening, while the local stresses generated by the deformation twinning is relaxed by stress induced martensite formation at the twin/matrix interface, promoting uniform elongation. This study highlights promising design strategies for high strength and strain hardenable Ti alloys
Nitrogen-vacancy centers in epitaxial laterally overgrown diamond: towards up-scaling of color center-based quantum technologies
No full textInternational audienceProviding high-quality, single-crystal diamond (SCD) with a large area is desirable for up-scaling quantum technology applications that rely on color centers in diamond. Growth methods aiming to increase the area of SCD are an active research area. Native color centers offer a sensitive probe for local crystal quality in such novel materials e.g. via their reaction to stress. In this work, we investigate individual native nitrogen-vacancy (NV) centers in SCD layers manufactured via laterally overgrowing hole arrays in a heteroepitaxially grown large-scale substrate. Heteroepitaxy has become a common tool for growing large SCDs; however, achieving the high crystal quality needed for quantum applications remains a challenge. In the overgrown layer, we identify NV centers with spin-decoherence times in the order of hundreds of µs, comparable to high-purity homoepitaxial SCD. We quantify the effective crystal stress in different regions of the overgrown layer, indicating a low stress overall and a stress reduction in the diamond layer above the holes
Rationally tailored passivation molecules to minimize interfacial energy loss for efficient perovskite solar cells
No full textInternational audienceLabor-intensive, trial-and-error methods are frequently employed for modifying the perovskite surface to mitigate trap defects. There is an urgent need for rationally designed and efficient molecular passivators. To address the performance and stability challenges caused by defects in polycrystalline perovskite, we have rationally designed and tailored passivation molecules, 4-(trifluoromethyl)benzoic anhydride (TFBA), ethyl 4-(trifluoromethyl)benzoate (TFB), and 4-(trifluoromethyl)benzoic acid (PTF), to minimize interfacial energy loss and modulate the bandgap alignment for achieving efficient perovskite solar cells (PSCs). These molecules could target the perovskite surface defects, particularly Pb–I antisite defects, with the –COOH and trifluoromethyl functional groups at the edges. Among them, PTF exhibited superior passivation performance by coordinating its carboxyl group with Pb 2+ , effectively suppressing non-radiative recombination. Additionally, the fluorine sites in these molecules corrected lattice distortions and stabilized the perovskite structure through hydrogen bonding with MA/FA cations, reducing ion migration, and enhancing moisture resistance. As a result, PTF-modified PSCs achieved an efficiency of 25.57% and maintained over 85% of their initial efficiency after 1 600 h of aging. This study provides a clear pathway for optimizing passivation strategies through rational molecular design
Synthesis, structure, and ionic transport properties of lithium monothiophosphate pentahydrate Li 3 PO 3 S·5H 2 O and its anhydrous form Li 3 PO 3 S
No full textInternational audienceMixed anion materials are promising for application as solid electrolytes in all-solid-state batteries, offering enhanced chemical and electrochemical stability alongside balanced ionic conductivity. This work reports a novel lithium oxythiophosphate Li3PO3S·5H2O, synthesized at a low temperature in an aqueous medium. The crystal structure and properties of Li3PO3S·5H2O were investigated through 3-dimensional electron diffraction, combined with powder X-ray and neutron diffraction, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, and electrochemical impedance spectroscopy. Li3PO3S·5H2O crystallizes in the hexagonal space group P63cm with a = 16.48462(4), c = 5.36224(2) Å, V = 1261.928(6) Å3, and Z = 6. 31P solid-state MAS NMR spectroscopy revealed the presence of pure and ordered PO3S tetrahedra. The dehydration of Li3PO3S·5H2O was studied via TGA and temperature-dependent XRD, demonstrating the formation of the anhydrous phase Li3PO3S at 200 °C. The conductivity of anhydrous Li3PO3S (2.6 × 10−6 S cm−1 at room temperature and Ea = 0.51 eV) is three orders of magnitude higher than that of the parent material Li3PO4 prepared by further heating the sample at 400°C, with a significantly lower activation energy. Our findings highlight the potential of mixed anion materials in improving solid electrolyte performance. This work brings new insight into the crystal chemistry of oxythiophosphate anions, which is key in developing fast ionic conductors for solid-state batteries
Electroactive Liquid Crystal Elastomers as Soft Actuators
No full textInternational audienceLiquid crystal elastomers (LCEs) combine the anisotropic properties of liquid crystals (LC) and elastic properties of elastomers. LCEs present outstanding thermotropic properties including large and reversible skeletal-muscle-like strain, tunable processability, and high programmability. LCEs are extensively studied and increasingly considered as one of the competitive smart soft materials. Most LCEs use heat or light as external stimulus, where the temperature variation or light illumination disrupts the LC order and further the anisotropy of LC polymer chain conformation to eventually get material actuation. However, besides heat and light, electrical energy is the most convenient and the most in demand stimulus in actuators. This review discusses all kinds of electroactive LCEs (eLCEs) reported in literature with the emphasis on their chemical structures, their alignment methods to get monodomain sample, the design of conducting materials and electrodes, their actuation mechanism and performance, which will be helpful for the future development of eLCEs. This review discusses eLCEs actuated by electromechanical, electrochemical, and electrothermal mechanisms. Among these, only electrothermal eLCEs involve intrinsic thermo-responsive expansion and contraction, which are induced by Joule heating through electronic and ionic conductive media incorporated into the LCEs. By contrast, electromechanical and electrochemical eLCEs operate as athermal electroactive systems
Improved modeling of battery electrolytes: betting on model fitting or quantum effects?
No full textInternational audienceThe accurate modeling of solvent dynamics and ionic interactions is of crucial importance for the development of novel electrolytes in next-generation metal-ion batteries. This study presents a critical evaluation of the semi-classical computational approach, the adaptive quantum thermal bath (adQTB) method, as a methodology for capturing the key properties of glyme-based solvents and their Ca2+-based electrolyte solutions. Simulations reveal that the adQTB method is particularly effective in accurately reproducing vibrational spectra, while offering good transferability across systems and conditions without requiring empirical parameter adjustments. In the context of electrolyte solutions, semi-classical adQTB simulations in combination with graph theory analysis indicate a distribution of the various charge-carrying clusters that is closely aligned with the conductivity measurements previously reported [Nguyen et al., Phys. Chem. Chem. Phys., 2022, 24, 21601], in sharp contrast to the empirically scaled force field. These findings emphasize the necessity of incorporating nuclear quantum effects for reliable electrolyte modeling, thereby paving the way for the advancement of post-Li battery technology
Charging Dynamics of Electric Double-Layer Nanocapacitors in Mean Field
No full textInternational audienceAn electric double-layer capacitor (EDLC) stores energy by modulating the spatial distribution of ions in the electrolytic solution that it contains. We determine the mean-field timescales for planar EDLC relaxation to equilibrium after a potential difference is applied. We tackle first the fully symmetric case, where positive and negative ionic species have the same valence and diffusivity, and then the general, more complex, asymmetric case. Depending on the applied voltage and salt concentration, different regimes appear, revealing a remarkably rich phenomenology relevant for nanocapacitors
Selection of Ruthenium Polypyridyl Complex-Modified Aptamers for Photodynamic Therapy against Streptococcus Pneumonia
No full textInternational audiencePhotodynamic therapy (PDT) harnesses the combination of light, oxygen, and photosensitizers to induce cell death via reactive oxygen species (ROS) formation. Given its intrinsic properties, PDT represents an alluring way of stymieing the increasing surge of antimicrobial resistance (AMR). Despite favorable assets, various hurdles need to be circumvented before PDT can efficiently be used to combat AMR. Here, we have evaluated the possibility of generating aptamers equipped with ruthenium polypyridyl complexes against entire Gram-positive Streptococcus pneumoniae bacteria. This combination is hypothesized to improve the poor specificity of photosensitizers, increase PDT efficiency, and potentially penetrate biofilms. Towards these aims, we first prepared nucleotides equipped with various ruthenium complexes and investigated their capacity at serving as substrates for polymerases for enzymatic DNA synthesis. Depending on the nature of the polypyridyl ligands, strong intercalation into dsDNA was observed even when connected to negatively charged nucleotide backbones. We then carried out SELEX and identified two unmodified aptamers that bound to the fixed bacterial target with Kd values of 118 nM and 541 nM. The SELEX experiment with the ruthenium-modified nucleotide led to the identification of one aptamer. The enzymatic synthesis of the modified aptamer was complicated by the formation of a very stable secondary structure confirmed by UV melting experiments (Tm of 84°C). The modified aptamer displayed a high affinity (Kd value of 125 nM) for fixed Streptococcus pneumoniae bacteria. Collectively, these results highlight the possibility of using nucleotides equipped with large modifications such as ruthenium polypyridyl complexes in SELEX to raise potent aptamers against entire bacterial targets. These findings open directions to convert aptamers into potent devices to combat AMR via PDT-based approaches
Pd-catalyzed dehydrogenative arylation of arylhydrazines to access non-symmetric azobenzenes, including tetra-ortho derivatives
No full textInternational audienceAzobenzenes are photoresponsive compounds widely used in molecular switches, light-controlled materials, and sensors, but despite extensive studies on symmetric derivatives, efficient methods for synthesizing non-symmetric analogues remain scarce due to regioselectivity issues, multistep procedures, and limited applicability to tetra-ortho-substituted structures. Herein, we describe a direct, one-pot Pd-catalyzed dehydrogenative C–N coupling between aryl bromides and arylhydrazines to access non-symmetric azobenzenes. The use of bulky phosphine ligands and sterically tuned substrates promotes selective N-arylation at the terminal nitrogen. The protocol tolerates a wide range of functional groups and enables the synthesis of well-decorated azobenzenes, including tetra-ortho-substituted derivatives. Notably, the reaction proceeds under an O2 atmosphere and in the presence of water, highlighting its robustness