Orateurs invités


 Benoit Guiffard (IETR Nantes) Flexoelectric energy conversion in soft polymer

Abstract: Flexoelectric effect in matter corresponds to an electrical polarization induced by a strain gradient. This transduction mechanism is expected to be exalted by enlarged strain gradients at small scales and also in the case of flexible compounds like soft polymers, which are able to withstand very large curvature. However, this presently understudied coupling remains weak in comparison with piezoelectric effect in organic films. In this talk we will present the flexoelectric effect in specific polymer films, with flexoelectric coefficients up to 1000 times larger than those actually measured in dielectric polymers, thus possibly allowing an alternative to piezoelectric materials. The methodology consists in using semi-conducting conjugated structures exhibiting high polarizability. Hence, enhancing both the interfacial and ionic polarizations in polymer films with soft treatments is a promising way to induce dipolar motion and free charges transport (i.e. large polarization changes) under strain gradient. The combination of the two functionalities- flexibility and enhanced flexoelectricity- would enable integration of these films in task-oriented devices for low frequency (<100 Hz) mechanical energy conversion.

Speaker's Bio:  Prof. B. Guiffard, Nantes University, France, Team co-leader of the « FunMAT » (Functional Materials) team, of the Institute of Electronics and digital Technologies (IETR)                   Benoit Guiffard joined the LGEF Laboratory at INSA, University of Lyon, France in 1996, where he obtained his Ph.D. degree in inorganic chemistry in 1999. He became an Associate Professor at INSA in 2000 when he worked on doped ferroelectric materials (ceramics, single crystals). His following research interests included the development of electroactive polymer composites exhibiting electromechanical coupling for environmental energy scavenging applications and large electric field actuation performance. In 2011, he has been hired as a Professor at the University of Nantes, France (IETR Lab, Functional Materials group), where he currently works on ferroelectric thin films and flexoelectric polymer composite films. The main target applications are the integration of functional materials in smart sensors and vibrating energy harvesting devices. Prof. B. Guiffard is the co-author of 4 patents, 84 articles in refereed journals and over 75 presentations on electroactive materials and applications.





Noëlle Gogneau (C2N Paris-Saclay) Electromechanical transducers based on GaN nanowires: Influence of the nanometer scale on the properties

Abstract: A new generation of piezoelectric generators based on 1D-nanostructures is appeared, these last years, to develop autonomous power micro-systems. Thanks to their high crystalline quality, their high mechanical properties and their large surface-to-volume, these nanostructures present advantages to significantly enhance the generator conversion efficiency. However, due to their nanoscale dimensions, the nanostructures are also characterized by “new” properties, non-significant at micrometric scales, that can lead to a strong modulation of their characteristics. In-depth understanding of these “new” properties is thus crucial. Here we use an advanced nano-characterization tool to investigate the relationship between the GaN nanowires characteristics and their piezoelectric conversion properties. The modulation of the free carrier concentration or the formation of nano-contact at the nanowire/electrode interface are examples of the nanoscale phenomena in play.

Speaker's Bio: Noelle Gogneau is a CNRS Research Director at the Center for Nanosciences and Nanotechnologies from Paris-Saclay University. Her research activities are centered on the growth of III-N NWs by Plasma Assisted – MBE and their characterization for Nano-Energy applications, with an emphasis on the development of a new generation of nano/piezo-generators. She is today an expert in the III-N NWs growth and the piezoelectric phenomena involving at nanometer scale. NG takes part to several projects among them the NanoVIBES (Flagship NanoSacalay 2020-24) and SCENIC (ANR-Project (2021-24)) projects as coordinator. She is also currently the chair of the European COST Action OPERA – “European Network for Innovative and Advanced Epitaxy” (2021-25; https://cost-opera.eu/) dedicated to the development of more efficient and cheaper devices and of new devices with new functionalities.

Author of 100 publications, her H-index is 23 (25) from Publon (Google Scholar).






Lionel Hirsch (IMS Bordeaux) - The boost of organic solar cells with Non-Fullerene Acceptors

Abstract: Organic bulk heterojunction photovoltaic solar cells (OPV), with record efficiency approaching 19% and proven high stability, are becoming a credible technology to participate in the global renewable energy bouquet. For more than a decade, only fullerene derivatives were used as electron acceptor materials. This class of materials has good electron transport properties thank to the spherical geometry that enhance the orbital overlap between fullerenes but as their optical absorption is very low, they don't participate to the photogeneration of current. The recent progresses on the OPV power conversion efficiency origin from the synthesis of new electron acceptor materials that combine both electron transport and optical absorption properties. In this context, OPV manufacturers need materials in sufficient quantity and certified quality. Batch-to-batch variations must be eliminated and impurities content should be carefully controlled, could them be organic or metallic traces. This presentation will show a description of the physics of OPV and the organic semiconductors in a first part. In a second part, we will focus on the effects of impurities in the raw semiconductor on solar cells. Our recent research will be presented describing our strategies to identify critical impurities and to estimate the tolerance threshold of solar cell. If initial post-fabrication efficiency of solar cells is obviously examined, our studies also explore the impurity effects on the stability of solar cells under illumination.

Speaker's Bio:  Lionel HIRSCH is CNRS director of research working on both organic and perovskite semiconductors-based devices. He has a material science and electrical engineering background and works at the IMS laboratory at the university of Bordeaux. His research interests are focused on the elucidation of charge transport mechanisms in organic semiconductors devices – organic and hybrid perovskite solar cells – organic field effect transistors – Interfaces in organic devices and temperature studies of electro-optical properties – Physico-chemical characterizations. He has published 130 papers in peer-reviewed international journals, 2 patents, 29 invited talks in national and international conferences.

More details are available on https://oembordeaux.cnrs.fr and www.ims-bordeaux.fr




 Didier Lasseux (I2M Bordeaux) Current production in porous microelectrodes: modelling towards an optimal material design.

Abstract: Porous materials are of special interest for the development of electro-devices such as bio-batteries, bio-actuators and bio-sensors, in particular for miniaturization purposes. Because of their potentially large specific area, these materials allow high current density production that can be several orders of magnitude larger than simple flat electrodes of comparable volume. Nevertheless, these materials have always been designed so far on an empirical basis regarding the thickness of the material and its pore size and organization. These parameters have a crucial impact on the competition between mass transfer, enzymatic turn-over and heterogeneous electron transfer rate. A way to progress in their optimization is to make use of modelling, in order to decipher the relationship between the microstructure and the macroscopic properties of the electrode. The presentation will show how this modelling approach through the scales can be performed in conjunction with material reconstruction based on image analysis and electroanalytical tests carried out on synthetized porous materials. Several different electro-chemical situations will be illustrated and an optimization procedure for the electrode macroscale dimensions will be reported. The overall procedure opens the way towards a rational recursive method of an optimal design for efficiency improvement of these devices.

Speaker's Bio: Didier Lasseux is a CNRS Research Director at I2M (Institut de Mécanique et d’Ingénierie – Dpt TREFLE), University of Bordeaux. His research is dediacted to transport phenomena in porous media, with a special accent on modelling at different scales, using upscaling methods. A special focus has been dedicated these last years to coupled transport and electrochemical mechanisms involved in porous electrodes and batteries. Among others, the aim is to elucidate the relationship between the micostructure of the materials and their macroscopic properties. He is the coordinator of the ANR project MOMA (ANR-17-CE08-0005) (MOdeling of Porous Electrodes for an Optimized MAterial Design). He is the co-funder of the International Society for porous media (InterPore), chair of the National Chapters committee of this society, and chair of the France InterPore Chapter (FIC). He authored and co-authored 95 articles in peer-reviewed journals, 6 patents, and around 180 presentations in conferences.










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