57 Use of doped-YAG nanoparticles as down-converters for Photovoltaics Olivier Raccurt 1 , Mervyn de Borniol 1 , Gilles Le Blevennec 1 , Eric Gerritsen 2 , Philippe Thony 2 , Zoe Tebby 3 1- CEA Grenoble, Department of Nano Materials, Laboratory for Nanochemistry and Nanosafety (DRT/LITEN/DTNM/LCSN), 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France) 2- CEA-INES, National Institute for Solar Energy, Technolac Solar Innovation Campus, 50 av. du Lac Léman, 73377 Le Bourget du Lac, France 3- CEA-Platform D2M, Laboratory for Surface Technology, 18 rue Benoit Lauras, 42000 Saint- Etienne, France ABSTRACT Increasing solar cell efficiency by using spectral conversion is addressed in this article. To that purpose rare-earth doped YAG nanoparticles exhibiting down-conversion and quantum cutting properties have been prepared. These nanoparticles have been synthesized with different concentrations of dopants in order to optimize the luminescence and the quantum cutting efficiency. Results on the incorporation of selected material into the encapsulating layer of c-Si based PV-modules are also presented. The effect of down-conversion has been demonstrated through the increase of photocurrent of encapsulated silicon solar cells. INTRODUCTION Increasing solar cell efficiency has been a constant challenge ever since the beginning of photovoltaic research in the 1950’s. It is known that solar spectrum and silicon cell efficiency exhibit poor overlapping below 500 nm. Generally, IR photons are not absorbed in solar cell semiconductor material whereas a large part of the UV photon energy is lost through thermalisation. Therefore, it is of great interest to convert the energy by down-conversion process using nanoparticles modified layer. Down-conversion is a process involving one high- energy photon ‘cuts’ into two photons of lower energy, referred to as quantum cutting. The relative amount of energy which can be regained by down-conversion has a thermodynamic limit of 8% absolute [1,2]. We focused our work on the down-conversion and quantum-cutting processes since no requirement of major changing in the cell technology is necessary. Typically, an efficient down-converter layer requires a high absorption in the range of 300 to 500 nm, luminescence close to the Si gap, high quantum efficiency with quantum cutting and optimum transparency in the rest of solar spectrum. This last point can only be achieved by using nanomaterials, transparent glass like vitroceramics or mono-crystals. Our research was focused on quantum cutting nanoparticles. They can be easily integrated into the existing steps of the cell or module manufacturing process. To achieve this goal, it has been shown that rare-earth compounds are suitable materials for quantum cutting [3]. As for example Ce 3+ and Yb 3+ in a Y 3 Al 5 O 12 (YAG) matrix is a suitable material [4], Ce 3+ has a broad absorption bands in the UV-blue region due to a strong ligand field and a high luminescent quantum efficiency close to 100% whereas Yb 3+ has an excited level energy (1.2 eV) roughly in accordance with the band gap of Si (1.1 eV). Mater. Res. Soc. Symp. Proc. Vol. 1303 © 2011 Materials Research Society DOI: 10.1557/opl.2011.407