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Tuning photoinduced electron transfers in polyoxometalate-based hybrids
No full textInternational audiencePolyoxometalates (POMs) form a remarkable class of well-defined nanosized oxoclusters with an unmatched diversity of structures and properties. An important property of POMs is their ability to reversibly accept and release specific numbers of electrons under minor structural rearrangement. Therefore, POMs are attractive candidates for the development of photochemical devices aiming at photocumulative electron transfer. In this context, we developed hybrid compounds in which photosensitizers (PS) are covalently connected to a POM and stimulate electron transfer to the oxocluster upon excitation. The photosensitized polyoxometalates display very promising photophysical properties. Notably the occurrence of photoinduced electron-transfer and the lifetime of the resulting charge separated state are strongly correlated to the redox properties of both components. This allows tuning the photophysical properties of the photoactive hybrid by drawing in the POM library. This will be presented along with our last results obtained with a family of POM-PS dyads and a photoactive POM-based mesogenic hybrid. We will describe the synthetic strategy and photophysical properties of this modular system as well as the development of preliminary molecular photocathodes, which constitutes a promising step for the development of charge photo-accumulation devices for artificial photosynthesis
Spectral Hole Burning in Eu:YSO for Low-frequency Acceleration Sensing
No full textInternational audienc
Focus point on scientific research in cultural heritage: articles from the 5th international conference on innovation in art research and technology (inArt 2022)
No full textInternational audienceAfter the postponement of the 2020 edition, the 5th International Conference on Innovation in Art Research and Technology - inArt 2022 was held from June 28th to July 1st, 2022, in Paris. Authors of the 47 oral presentations and 119 posters presented were invited to submit articles for publication in EPJ+. This EPJ+ Focus Point on “Scientific Research in Cultural Heritage” brings together 33 papers resulting from this process. These articles illustrate the wide range of topics covered at the conference, which fall within the scope of archaeometry or conservation science. This editorial briefly presents these articles, which have been brought together under the following three thematic headings: comprehension of materials and techniques involved in Cultural Heritage; degradation mechanisms and conservation strategies and in situ experiments and mobile instrumentation. Bearing in mind that this is only a way of presenting the articles and not a formal classification of their content, given the overlap of these different aspects in several of the studies presented
Integration of a Ruthenium-based Alcohol Dehydrogenation Catalyst in an all-Molecular CO2 Electrolyzer
No full textThe electrification of chemical processes using renewable feedstocks and energy sources represents a key strategy toward a sustainable chemical industry. Coupling CO2 electroreduction (CO2RR) with anodic alcohol oxidation offers an interesting route to reduce energy consumption and increase product value while circumventing the limitations of water oxidation. Here, we report a fully molecular co-electrolysis platform employing a well-defined ruthenium pincer-based alcohol dehydrogenation catalyst immobilized on carbonaceous support. The system enables the selective electrooxidation of ethanol to acetate with exceptional mass activities exceeding 2 A mg-1, thus outperforming previously reported molecular anode catalysts and competing with state-of-the- art materials. When paired with cathodic CO2-to-CO conversion using a molecular cobalt phthalocyanine catalyst, the integrated electrolyzer achieves co-production of acetate and CO at high rates. While long-term operational stability remains limited (<1 h), detailed electrochemical and spectroscopic analyses reveal main degradation pathways of the molecular anode, offering guidance for future improvements. These results establish a performance benchmark for molecular anodic electrocatalysis and underscore the potential of integrated electrosynthetic approaches based on well- defined active site
Multi-temperature hot carrier solar cell: an issue or an opportunity?
No full textInternational audienceA hot-carrier solar cell (HCSC) is a high-efficiency photovoltaic concept where electrons and holes are at a higher temperature than the lattice. If this temperature is converted into voltage through a thermoelectric conversion, these hot carriers can result in higher cell efficiency, possibly allowing to reach the thermodynamic limit of 86% [1]. This gives the two requirements for a HCSC: establishing a hot-carrier population and converting the temperature into extra voltage through energy-selective contacts. On the first aspect, one should consider the generation of the hot carriers, and the design of absorbers that can make this generation easier. In most previous approaches to hot carrier solar cell, e.g. [2], carriers are assumed to form quasi thermal distributions with temperature larger than that of the lattice (Te = Th > Tamb). However, because different carriers may have different effective masses and different coupling with the phonons, the possibility of having Te ≠ Th must be addressed [3]. We present here the how such a situation can be modelled, experimentally studied and we present then a characterization of a such two-temperatures absorber [4] and the impact on the operation of HCSC [5].We propose a purely optical method which allows the direct and distinct estimation of electron and hole temperatures in steady state, published in [4]. This technique, based on photoluminescence, relies on the precise determination of the band-filling signature. We apply this technique to an InGaAsP single quantum well. Electron temperature surpasses 1000 K at largest excitation intensity, while holes remain colder, close to lattice temperature. Nonetheless, the increase in hole temperature is too large to be explained purely by photon absorption, demonstrating an energy transfer from electrons to holes (fig 1). On the second aspect, we address the question of the operation of a HCSC in the regime where electrons are hotter than holes [5]. For that purpose, we develop a two-temperature HCSC model and study its efficiency and sensitivity to the energy-selective contact design. We show that the two-temperature HCSC is always more efficient than the one-temperature one (fig 2). We also present how the theory can be extended to include these cases and discuss what are the relevant key parameters to be considered in such a situation.Actual hot carrier devices would deviate from ideal assumptions of the initial idea of Ross and Nozik [1]. We will finally explore how resilient is the hot carrier device concept to such deviations.[1] R. T. Ross and A. J. Nozik. ‘Efficiency of hot-carrier solar energy converters’. Journal of Applied Physics, vol. 53, no. 5, pp. 3813–3818 (1982)[2] A. Lebris et al. APL 2010[3] F. Gibelli, L. Lombez and J.-F. Guillemoles. ‘Two carrier temperatures non-equilibrium generalized Planck law for semiconductors’. Physica B: Condensed Matter, vol. 498, pp. 7–14 (2016)[4] Thomas Vezin, Nathan Roubinowitz, Laurent Lombez, Jean-François Guillemoles, and Daniel Suchet, ‘Direct determination of electron and hole temperatures from continuous-wave photoluminescence measurement’, Physical Review B (2024)[5] Thomas Vezin, PhD thesis, chap. 6 ‘Operation, design and resilience of a two-temperature hot carrier solar cell’ (2024
Enhanced magnetic field sensitivity of shallow NV ensembles via high-temperature implantation
No full textInternational audienceDense and shallow ensembles of negatively charged nitrogen-vacancy centers (NV) with good optical and spin properties play a key role in the performance enhancement of diamond-based quantum sensors. Ion implantation enables precise control of NV depth and density. However, at high ion fluence, this method is limited by low NV creation yields and sample amorphization. Additionally, shallow NV spin properties deteriorate due to surface proximity. In this paper, we study N ion implantation at energies between 10 and 15 keV with fluences as high as 1e15 ions/cm2 at temperatures of 20, 400 and 800°C to investigate the influence of implantation temperature on lattice damage, NV creation yield and NV spin properties. Our results show that diamond maintains structural integrity at 800°C with fluences up to 1e15 ions/cm2 without amorphization. Furthermore, high-temperature implantation improves NV creation yields up to five times without compromising T2, T2 and T1, making it a promising approach to enhance the magnetic field sensitivity of NV ensembles
Amorphous GaN matrix embedded nanocrystals exhibiting bulk bandgap luminescence
No full textInternational audienceThis work reports on the room temperature sputtering growth of gallium nitride thin films, exhibiting band edge luminescence without thermal annealing or post-deposition processing. In particular, we investigate and correlate their luminescence spectra with their structural properties (amorphous or polycrystalline phases), the presence of defects, and the grain features by combining cathodoluminescence and HR-TEM characterizations. The working pressure and Ar/N2 flow ratio are found to have a profound effect on both the structural and optical properties of the films. Notably, the only film with band edge luminescence is grown at the highest investigated pressure (13.3 Pa) and 40% N2 concentration and exhibits single-grained crystallites of small sizes (∼5 nm). Moreover, this polycrystalline film has an almost equal fraction of amorphous and crystalline phases. This suggests that the presence of smooth and nanometer-sized crystals in an amorphous matrix (inducing grain surface passivation) could be a synergetic combination to achieve luminescent films grown at room temperature
Solvation Entropy as a Lever for Steering the Macroscopic Properties of a Functional Supramolecular Helical Polymer
No full textInternational audienceSolvent‐solute interactions are utterly important in supramolecular polymers (SPs), yet the high responsivity of SPs to solvent polarity makes it challenging to play on other solvation effects to tune their macroscopic properties in a rational manner. Herein, we report the characterization at various scales of the assembly properties of a C 2 ‐symmetric benzene‐1,3,5‐tricarboxamide monomer with two (1 S )‐methylheptyl moieties and one diphenylphosphino group as lateral chains. Our investigation reveals a highly cooperative structural transition between two SP states, which can exquisitely be tuned by solvents of similar polarities, leading to variation of the transition temperature (T*) over a range of 85 K. The structural transition was detected in 4 pure solvents and 13 toluene/cosolvent mixtures; a fair relationship is determined between T* and the solvent molar volume. The transition is only weakly favored by enthalpy (by ca. 2 kJ.mol −1 at 286 K). However, minimization of the entropic cost leads to a notable increase in the T*. This allows a fine tuning of the thermothickening and catalytic properties of the resulting SPs auguring that solvation, and notably solvation entropy, may constitute an important lever for steering SPs structure and properties
Impact of (NH4)2SO4 agricultural atmospheric pollutant on the degradation mechanisms of thin layer Cu(In,Ga)Se2 solar cells
No full textInternational audienceChemical environment is usually disregarded in stability evaluations of photovoltaic devices but it can be critical for agrivoltaics (dual land use for energy production and agriculture). This work considers for the first time the effect of (NH4)2SO4 agricultural pollutant on the chemical degradation mechanisms of thin layer solar cells. Cu(In,Ga)Se2 (CIGS) cells with the architecture SLG/Mo/CIGS/Zn(O,S)/ZnMgO/Al:ZnO/NiAlNi and representative stacks were characterized at different times of temperature/humidity cyclic aging with and without (NH4)2SO4. The pollutant strongly increased degradation rate and modified the key degradation mechanisms. Cu(In,Ga)Se2-absorber and its interface with Mo-back contact were the most affected by accelerated aging without (NH4)2SO4, while corrosion of front NiAlNi contacts and pitting of window Al-doped ZnO layer was the key degradation mechanism in the presence of (NH4)2SO4. Chemical modifications of the cell and layers were coherent with optoelectrical characteristics loss. The work implies the necessity to take into account specific agricultural pollutants in reliability evaluation of new technologies for agrivoltaic applications
Innovative Nb-Doped SnO 2 Electron Transport Layers Prepared by Atomic Layer Deposition for Enhanced Perovskite Solar Cells
No full textInternational audienceRapid advancements in perovskite solar cell (PSC) technology have highlighted the critical role of precise interface engineering in enhancing device stability and performance. Metal oxide-based electron transport layers (ETLs) prepared by atomic layer deposition (ALD) have emerged as promising candidates for improving PSC efficiency and stability. In this study, Nb-doped SnO2 (SnO2:Nb) thin films fabricated by ALD were employed as ETLs in n-i-p architecture PSCs. By leveraging the atomic-level control of ALD, the optoelectronic properties of SnO2:Nb thin films were finely tuned through controlled Nb doping, significantly influencing the photovoltaic (PV) performance of the devices in threshold behavior. PSCs incorporating SnO2:Nb thin film ETLs with low Nb atomic contents (≤0.2 at. %) exhibited improved performance, with an absolute increase in power conversion efficiency (PCE) of 0.93%, primarily due to increased Voc and Jsc values. Half-cell and extensive characterizations, including dark J–V curves, external and internal quantum efficiencies, impedance spectroscopy, and steady-state and time-resolved photoluminescence, were conducted to elucidate the effect of Nb doping. The perovskite layer was found to remain unaffected by ETL modification. The performance enhancement is attributed to the improved electrical properties of ETL thin films, leading to reduced series resistance and increased shunt resistance, as well as the reduction of interface defects, alteration of decay times, and favorable band alignments. These findings highlight the potential of ALD-processed SnO2-based ETLs for next-generation PSCs