Projet de thèse en 2MGE : Matériaux, Mécanique, Génie civil, Electrochimie
Sous la direction de Jean-luc Deschanvres.
Thèses en préparation à Grenoble Alpes en cotutelle avec l'Instituto Superior Técnico Lisbon , dans le cadre de I-MEP2 - Ingénierie - Matériaux, Mécanique, Environnement, Energétique, Procédés, Production , en partenariat avec LMGP - Matériaux et génie physique (laboratoire) depuis le 12-09-2011 .
High efficiency solar cells require the absorption of photons in the full solar spectrum. Since the band gap of amorphous silicon lies around 1.8 eV, photons of lower energy do not add to the generation of EHPs and hence to the photocurrent within the p-n junction. The low energy part of the solar spectrum however, can be accessed by using up-conversion (UpC) processes. The phenomenon of UpC, i.e. the generation of higher energy photons by excitation of photons of lower energy in active materials, is described extensively in the recent literature. The conversion of NIR light into visible radiation can be realized by doping rare earth ions (RE) into a solid. A number of different mechanisms have been proposed for the generation of anti-Stokes shifted photons. These include excited state absorption (ESA), energy transfer UpC (ETU), cooperative effects, classical second harmonic generation (SHG) and two-photon absorption (TPA). However, the efficiency of the UC process depends strongly on the host lattice. In the present work, lanthanide f-ions, in particular Er(3+) and Yb(3+) ions, are doped within aluminosilicate, titania, yttria and yttrium fluoride host lattices and investigated for their ability of showing UC. The thin films are deposited on Si wafers, as well as transparent substrates, by the sol-gel method at IST Lisbon, and two different MOCVD variants in Grenoble. The as-obtained films are spectroscopically characterized by photoluminescence spectroscopy, FTIR, ellipsometry and XRD.
Improvement of solar cell efficiency by up-conversion based on RE doping
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