Screen-printed flexible MRI receive coils.

Magnetic resonance imaging is an inherently signal-to-noise-starved technique that limits the spatial resolution, diagnostic image quality and results in typically long acquisition times that are prone to motion artefacts. This limitation is exacerbated when receive coils have poor fit due to lack of flexibility or need for padding for patient comfort. Here, we report a new approach that uses printing for fabricating receive coils. Our approach enables highly flexible, extremely lightweight conforming devices. We show that these devices exhibit similar to higher signal-to-noise ratio than conventional ones, in clinical scenarios when coils could be displaced more than 18 mm away from the body. In addition, we provide detailed material properties and components performance analysis. Prototype arrays are incorporated within infant blankets for in vivo studies. This work presents the first fully functional, printed coils for 1.5- and 3-T clinical scanners

Flexible and stretchable power sources for wearable electronics.

Flexible and stretchable power sources represent a key technology for the realization of wearable electronics. Developing flexible and stretchable batteries with mechanical endurance that is on par with commercial standards and offer compliance while retaining safety remains a significant challenge. We present a unique approach that demonstrates mechanically robust, intrinsically safe silver-zinc batteries. This approach uses current collectors with enhanced mechanical design, such as helical springs and serpentines, as a structural support and backbone for all battery components. We show wire-shaped batteries based on helical band springs that are resilient to fatigue and retain electrochemical performance over 17,000 flexure cycles at a 0.5-cm bending radius. Serpentine-shaped batteries can be stretched with tunable degree and directionality while maintaining their specific capacity. Finally, the batteries are integrated, as a wearable device, with a photovoltaic module that enables recharging of the batteries

Conception, characterization and lifetime of tandem organic solar cells based on PCDTBT

Pour être viable économiquement, les cellules photovoltaïques organiques doivent dépasser 10 % de rendement et atteindre plusieurs milliers d'heure de durée de vie. Les cellules tandems constituent une voie probante d'augmentation des rendements. Ce travail de thèse a pour objectifs l'élaboration de cellules organiques tandems puis l'étude de leur fonctionnement et de leur vieillissement. Dans un premier temps, les paramètres gouvernant le rendement de cellules photovoltaïques organiques sont examinés sur le modèle de cellules simples à base de PCDTBT. Des caractérisations s'appuyant sur la spectroscopie d'impédance mettent en valeur le rôle joué par chacune des couches constitutives de la cellule. Dans un deuxième temps, un protocole de fabrication des cellules tandems connectées en série est établi. Celui-ci traite successivement les trois points critiques pour l'efficacité des tandems : choix des polymères aux absorptions complémentaires, puis mise au point de la couche intermédiaire (CI) et enfin optimisation des épaisseurs. Une attention particulière est portée au fonctionnement de la CI. Pour optimiser les épaisseurs, un programme de simulation des phénomènes optiques est élaboré et ses prédictions comparées aux résultats expérimentaux. Enfin, le vieillissement des cellules simples et tandems est étudié sur des temps de plusieurs centaines ou milliers d'heures. Les diminutions de performances observées sont liées à la dégradation des couches d'interface tandis que la couche active semble stable. Les cellules tandems organiques présentent un fort potentiel pour l'obtention de rendements élevés et stables dans le temps.In order to reach commercialization, organic photovoltaic solar cells need to reach efficiencies above 10 % and achieve lifetimes of several thousands of hours. Tandem solar cells are a way of improving the efficiencies. The objectives of this work are therefore to study the fabrication process, the operation and the ageing of organic tandem solar cells. First, single solar cells based on the active material PCDTBT are used as model to investigate the factors governing the cells efficiencies. Using characterization techniques such as impedance spectroscopy, the roles played by each layer of the cells are identified. Based on these results, a protocol to make series tandem cells is developed. Each of its steps is dedicated to treating a key aspect of tandem cells : choice of complementary absorbing polymers, design of the intermediate layer (IML) and thickness optimization. The functioning of the IML is subjected to a particular attention. To optimize the thicknesses, optical phenomena are numerically simulated. The prediction thus made are then compared to experimental results. Finally, the ageing of single and tandem cells is investigated on time spans ranging from several dozens to several thousands of hours. It is shown that the device degradation can be linked to poor ageing of the interface layers, while the active layer stays stable. Organic tandem cells are promising candidates to reach both high efficiencies and long lifetime

Conception, caractérisation et durée de vie de cellules photovoltaïques organiques tandems à base de PCDTBT

In order to reach commercialization, organic photovoltaic solar cells need to reach efficiencies above 10 % and achieve lifetimes of several thousands of hours. Tandem solar cells are a way of improving the efficiencies. The objectives of this work are therefore to study the fabrication process, the operation and the ageing of organic tandem solar cells. First, single solar cells based on the active material PCDTBT are used as model to investigate the factors governing the cells efficiencies. Using characterization techniques such as impedance spectroscopy, the roles played by each layer of the cells are identified. Based on these results, a protocol to make series tandem cells is developed. Each of its steps is dedicated to treating a key aspect of tandem cells : choice of complementary absorbing polymers, design of the intermediate layer (IML) and thickness optimization. The functioning of the IML is subjected to a particular attention. To optimize the thicknesses, optical phenomena are numerically simulated. The prediction thus made are then compared to experimental results. Finally, the ageing of single and tandem cells is investigated on time spans ranging from several dozens to several thousands of hours. It is shown that the device degradation can be linked to poor ageing of the interface layers, while the active layer stays stable. Organic tandem cells are promising candidates to reach both high efficiencies and long lifetime.Pour être viable économiquement, les cellules photovoltaïques organiques doivent dépasser 10 % de rendement et atteindre plusieurs milliers d'heure de durée de vie. Les cellules tandems constituent une voie probante d'augmentation des rendements. Ce travail de thèse a pour objectifs l'élaboration de cellules organiques tandems puis l'étude de leur fonctionnement et de leur vieillissement. Dans un premier temps, les paramètres gouvernant le rendement de cellules photovoltaïques organiques sont examinés sur le modèle de cellules simples à base de PCDTBT. Des caractérisations s'appuyant sur la spectroscopie d'impédance mettent en valeur le rôle joué par chacune des couches constitutives de la cellule. Dans un deuxième temps, un protocole de fabrication des cellules tandems connectées en série est établi. Celui-ci traite successivement les trois points critiques pour l'efficacité des tandems : choix des polymères aux absorptions complémentaires, puis mise au point de la couche intermédiaire (CI) et enfin optimisation des épaisseurs. Une attention particulière est portée au fonctionnement de la CI. Pour optimiser les épaisseurs, un programme de simulation des phénomènes optiques est élaboré et ses prédictions comparées aux résultats expérimentaux. Enfin, le vieillissement des cellules simples et tandems est étudié sur des temps de plusieurs centaines ou milliers d'heures. Les diminutions de performances observées sont liées à la dégradation des couches d'interface tandis que la couche active semble stable. Les cellules tandems organiques présentent un fort potentiel pour l'obtention de rendements élevés et stables dans le temps

Evaluation of indoor photovoltaic power production under directional and diffuse lighting conditions

International audienc

Polymer solar cells with electrodeposited CuSCN nanowires as new efficient hole transporting layer

International audienc

Evaluation of a Flexible 12-Channel Screen-printed Pediatric MRI Coil.

Background Screen-printed MRI coil technology may reduce the need for bulky and heavy housing of coil electronics and may provide a better fit to patient anatomy to improve coil performance. Purpose To assess the performance and caregiver and clinician acceptance of a pediatric-sized screen-printed flexible MRI coil array as compared with conventional coil technology. Materials and Methods A pediatric-sized 12-channel coil array was designed by using a screen-printing process. Element coupling and phantom signal-to-noise ratio (SNR) were assessed. Subjects were scanned by using the pediatric printed array between September and November 2017; results were compared with three age- and sex-matched historical control subjects by using a commercial 32-channel cardiac array at 3 T. Caregiver acceptance was assessed by asking nurses, technologists, anesthesiologists, and subjects or parents to rate their coil preference. Diagnostic quality of the images was evaluated by using a Likert scale (5 = high image quality, 1 = nondiagnostic). Image SNR was evaluated and compared. Results Twenty study participants were evaluated with the screen-printed coil (age range, 2 days to 12 years; 11 male and nine female subjects). Loaded pediatric phantom testing yielded similar noise covariance matrices and only slightly degraded SNR for the printed coil as compared with the commercial coil. The caregiver acceptance survey yielded a mean score of 4.1 ± 0.6 (scale: 1, preferred the commercial coil; 5, preferred the printed coil). Diagnostic quality score was 4.5 ± 0.6. Mean image SNR was 54 ± 49 (paraspinal muscle), 78 ± 51 (abdominal wall muscle), and 59 ± 35 (psoas) for the printed coil, as compared with 64 ± 55, 65 ± 48, and 57 ± 43, respectively, for the commercial coil; these SNR differences were not statistically significant (P = .26). Conclusion A flexible screen-printed pediatric MRI receive coil yields adequate signal-to-noise ratio in phantoms and pediatric study participants, with similar image quality but higher preference by subjects and their caregivers when compared with a conventional MRI coil. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Lamb in this issue

Origin of the S‑Shape upon Aging in Standard Organic Solar Cells with Zinc Oxide as Transport Layer

International audienceIn standard organic solar cells, an electron transporting layer (ETL) is often inserted between the active layer and the cathode in order to achieve good performances. In this work, a zinc oxide (ZnO) ETL is used with an aluminum cathode, yielding functional fresh cells. However, upon storage in the dark and inert atmosphere, an S-shape quickly appears in the J−V curves, leading to a sharp decline of the solar conversion efficiency. By building cells with various ETL sequences, we show that the S-shape stems from a modification of the ZnO/Al interface. Further experiments using Kelvin probe force microscopy (KPFM) and X-ray photoelectron spectroscopy (XPS) suggest that the source of this phenomenon is the appearance of an aluminum oxide layer at the ZnO/Al interface, which could result from a red−ox reaction between the two materials