Production and Characterization of Tb 3 +/Yb 3 + Co-Activated AlON Thin Films for Down Conversion Applications in Photov
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Production and Characterization of Tb3+/Yb3+ Co-Activated AlON Thin Films for Down Conversion Applications in Photovoltaic Cells K. Tucto1, L. Flores1, J. Guerra1, 2, J. Töfflinger1, J. Dulanto1, R. Grieseler3, A. Osvet2, M. Batentschuk2, R. Weingärtner1 1
Departamento de Ciencias, Sección Física, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, Lima 32, Perú 2 Department of Material Science 6, University of Erlangen-Nuremberg, Martenstr. 6, Erlangen 91058, Germany 3 Chair Materials for Electronics, Institute of Materials Engineering and Institute of Micro and Nanotechnologies MacroNano, TU Ilmenau, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau, Germany ABSTRACT Terbium and ytterbium co-doped aluminum oxynitride thin films were grown onto silicon substrates using radiofrequency magnetron sputtering. Aluminum oxynitride samples doped with 4.6 at. % of Yb3+ and co-doped with 0.4 at. % of Tb3+ were obtained. The prepared samples were annealed from 150ºC to 850ºC in steps of 100ºC. By using energy dispersive X-ray analysis we measured the sample composition and the doping concentration. The emission intensities at different annealing temperatures were characterized using photoluminescence measurements upon excitation at 325 nm. The 5D4 7F5 main transition of Tb3+ and the characteristic near infrared emission at 980 nm of Yb3+ were recorded. In order to study the luminescence behavior of the samples in terms of a down conversion process, we have plotted the integrated areas of the main transition peaks versus the annealing temperature. INTRODUCTION The most widely used solar cells are based on crystalline silicon (c-Si). However, the band gap energy of silicon semiconductor restricts the energy absorption to an almost half of the available solar spectrum. The spectral response of silicon based solar cell dominates in the range of 350 nm to 1100 nm, and a maximum is reached at 890 nm. The external quantum efficiency of silicon based solar cell has minimum at wavelengths 350 nm and 1100 nm, and reaches a maximum at 590 nm [1]. This leads that photons with energies lower than the band gap energy of silicon cannot be absorbed, while photons with larger energies loose the excess of energy by thermalization of electron hole pairs [2-4]. With the aim to achieve maximal exploitation of sunlight by the c-Si solar cell, the concept of energy converter devices using rare earth ions for spectral conversion in solar cells, has emerged [4-6]. The down-conversion (DC) process circumvents the strong limitation of efficiency by carrier thermalization and surface recombination in the ultraviolet (UV) and blue range of sunlight by converting one high-energy photon into two near-infrared (NIR) photons, thereby enhancing the spectral response of the c-Si solar cell [4, 7]. The cooperative energy transfer (CET) from the 5D4 level of Tb3+ to 2F5/2 levels of two Yb3+ ions for NIR down-conversion has been recognized using optical spectroscopy and was reported in various hosts, such as Tb3+/Yb3+ co-doped phosphors [8, 9], fluorite gl
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