Projet de thèse en Electronique et Optoélectronique, Nano- et Microtechnologies
Sous la direction de Stephane Collin.
Thèses en préparation à Paris Saclay , dans le cadre de École doctorale Electrical, optical, bio-physics and engineering (Orsay, Essonne ; 2015-....) , en partenariat avec Centre de Nanosciences et de Nanotechnologies (laboratoire) , Photonique (equipe de recherche) et de Université Paris-Sud (établissement de préparation de la thèse) depuis le 30-09-2017 .
Nanostructured materials are becoming a game changer for next generation photovoltaics. They enable the development of ultrathin solar cells (light-trapping), tandem solar cells (direct growth of III-V on Si) and new concepts for high-efficiency (quantum semiconductor structures for hot-carriers and intermediate-band solar cells). However, their development is hindered by the lack of direct characterization techniques. A new cathodoluminescence (CL) setup has been installed at C2N/Marcoussis at the end of 2015. Its basic principle is the following (see the figure): a material is excited with an electron beam in a scanning electron microscope (SEM), providing a spatial resolution of 10nm. Secondary electrons (SE), emitted photons (CL) and even electron-beam-induced current (EBIC) are collected and recorded simultaneously in order to form 2D maps. For each spatial position, CL spectra provide information on the luminescence efficiency, band structure and defects. In our tool, laser-controlled bunches of electrons can also be used for excitation instead of a continuous beam, resulting in time-resolved CL measurements (TRCL) that provide valuable information on carrier dynamics and lifetime. Our CL/TRCL setup has state-of-the-art specifications and is extremely versatile: wide ranges of wavelengths (200nm-1600nm) and temperatures (10K-400K), time-resolved measurements (temporal resolution 10ps). In addition, its very high collection efficiency on a wide field of view is perfectly adapted to CL and TRCL mapping of a wide variety of photovoltaic materials: defects and quantum structures (quantum wells, quantum dots, ) in bulk materials, polycrystalline semiconductors (CdTe, CIGS, ), nanomaterials (nanowires, nanopillars, ),...
Nanomaterials for high-efficiency photovoltaics
The goal of this PhD project is to investigate the properties of new materials and architectures for high efficiency photovoltaics: III-V nanowires, localized ohmic contacts, passivation layers, This work will be based on the development of novel characterization methodologies based on cathodoluminescence, time-resolved cathodoluminescence, and EBIC mapping. The candidate will be involved in current projects on thin-film and ultrathin solar cells (GaAs, CIGS, CdTe), nanowire and tandem (III-V/Si) solar cells. He will also contribute to the fabrication and modeling of photovoltaic materials and devices. This work will be performed in the framework of several national (ANR) and international (H2020) projects and collaborations (NREL, Fraunhofer ISE, RCAST), and in close collaboration with several partner labs of the new Institut photovoltaïque d'Ile-de-France (IPVF).