PhD defense
Fabrication and investigation of III-V quantum structured solar cells with Fabry-Perot cavity and nanophotonics in order to explore high-efficiency photovoltaic concepts
UPMC -C2N-IRDEP, Chimie ParisTech,PhD defense
In the past decade, photovoltaics (PV) has become a key player for the future of worldwide energy generation. Innovation in PV is likely to rely on high efficiency PV with flexible and lightweight thin films to enable PV deployement for mobile applications. In the framework of the Japanese- French laboratory “NextPV”, this thesis investigates the development of III-V quantum structured solar cells to explore high-efficiency photovoltaic concepts especially intermediate band solar cells (IBSC). Quantum structured IBSC have proven to be limited by thermal escape at room temperature and by low subbandgap light absorption. Following a consistent approach, we evaluate the topolo- gy, thermal escape mechanism, quantum structure and optical absorption of In(Ga)As quantum dots in a wide gap Al0.2GaAs host material. We also characterize quantitatively the device operation and improve the optical design. For a high irradiation, we evidence a hot carrier population in the quan- tum dots. At the same time, sequential two-photon absorption (S-TPA) is demonstrated both opti- cally and electrically. We also show that S-TPA for both sub-bandgap transitions can be enhanced by a factor x5-10 with light management techniques, for example by implementation of Fabry-Perot cavities with the different epitaxial transfer methods that we developed. More advanced periodical nanostructures were also fabricated in the case of multi-quantum well solar cells using nanoimprint lithography techniques. Overall we discuss the possibility of realizing intermediate-band-assisted hot-carrier solar cells with light management to open the path for high-efficiency quantum struc- tured IBSC.
Jury member :
Christian SEASSAL
Guilhem ALMUNEAU Christophe SAUVAN Alexandra FRAGOLA Yoshitaka OKADA
Stéphane COLLIN Jean-François GUILLEMOLES
Directeur de Recherche (INL, Lyon)
Chargé de Recherche (LAAS, Toulouse) Chargé de Recherche (LCF, Paris-Saclay) Maître de conférences (UPMC, Paris) Professeur (RCAST, Tokyo)
Chargé de Recherche (C2N, Paris-Saclay) Directeur de Recherche (IPVF, Paris-Saclay)
Rapporteur Rapporteur Examinateur Examinateur Examinateur Directeur de thèse Directeur de thèse
(in french)
C2N -Site Orsay, Salle 044 (P. Grivet), Orsay CedexPhD defense
(in french)
C2N -Site Orsay, C2N-Site orsay, Orsay CedexPhD defense
Composition of the jury
Rapporteur Pr. Ian O'Connor École Centrale de Lyon
Rapporteur Dr. Alexandre Pitti CNRS, Université de Cergy-Pontoise Examinateur Denis Crété UMR CNRS/Thales
Examinatrice Dr. Julie Grollier UMR CNRS/Thales
Examinateur Dr. Gilles Sassatelli CNRS, Université Montpellier 2 Directeur de thèse Dr. Damien Querlioz CNRS, Université Paris-Sud Invité Dr. Nicolas Locatelli Lycée Gustave Eiffel, Cachan
Abstract
With the advent of "artificial intelligence", computers, mobile devices and other connected objects are being pushed beyond the realm of arithmetic and logic operations, for which they have been optimized over decades, in order to process "cognitive" tasks such as automatic translation and image or voice recognition, for which they are not the ideal substrate. As a result, supercomputers may require megawatts to process tasks for which the human brain only needs 20 watt. This has revived interest into the design of alternative computing schemes inspired by the brain. In particular, neural oscillations that appear to be linked to computational activity in the brain have inspired approaches leveraging the complex physics of networks of coupled oscillators in order to process cognitive tasks efficiently. In the light of recent advances in nano- technology allowing the fabrication of highly integrable nano-oscillators, this thesis proposes and studies novel neuro-inspired oscillator-based pattern classification architectures that could be implemented on chip.
(in french)
Ecole Polytechnique, Amphithéatre Monge, PalaiseauPhD defense
(in french)
C2N -Site Orsay, C2N-Site orsay, Orsay CedexPhD defense
(in french)
C2N - Site Marcoussis, C2N site Marcoussis, salle R. Planel, MarcoussisPhD defense
Electric field control of domain wall dynamics
C2N -Site Orsay, C2N-Site orsay, Orsay CedexPhD defense
Electric (E) field control of magnetism in ferromagnetic thin films has attracted great attention as a promising feature that could reduce the energy consumption of novel spin- tronic devices. In particular, electrical control of magnetic anisotropy, and therefore magnetic domain wall (DW) dynamics, is intensively studied in view of applications in low-power electrical magnetization switching.
In this work, I will show a device design based on ionic liquid gating of CoFeB/MgO/HfO2 thin films that allows for an E-field controlled reorientation of the anisotropy easy axis of up to 90◦. Ionic liquid gating is the key to the large anisotropy modulation that these devices can provide. This strong E-field effect was employed to achieve voltage control of magnetic domain wall velocity, pinning and domain nucleation in liquid gated magneto- electric devices.
(in french)
Université Pierre et Marie Curie, Place Jussieu, ParisPhD defense
(in french)
C2N -Site Orsay, C2n -site Orsay, Orsay CedexPhD defense
(in french)
C2N -Site Orsay, C2N-Site orsay, Orsay CedexPhD defense