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Proceedings Paper

Comprehensive analysis of photonic effects on upconversion of β-NaYF4:Er3+ nanoparticles in an organic-inorganic hybrid 1D photonic crystal
Author(s): C. L. M. Hofmann; S. Fischer; C. Reitz; B. S. Richards; J. C. Goldschmidt
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Paper Abstract

Upconversion (UC) presents a possibility to exploit sub-bandgap photons for current generation in solar cells by creating one high-energy photon out of at least two lower-energy photons. Photonic structures can enhance UC by two effects: a locally increased irradiance and a modified local density of photon states (LDOS). Bragg stacks are promising photonic structures for this application, because they are straightforward to optimize and overall absorption can be increased by adding more layers. In this work, we present a comprehensive simulation-based analysis of the photonic effects of a Bragg stack on UC luminescence. The investigated organic-inorganic hybrid Bragg stack consists of alternating layers of Poly(methylmethacrylate) (PMMA), containing purpose-built β-NaYF4:25% Er3+ core-shell nanoparticles and titanium dioxide (TiO2). From optical characterization of single thin layers, input parameters for simulations of the photonic effects are generated. The local irradiance enhancement and modulated LDOS are first simulated separately. Subsequently they are coupled in a rate equation model of the upconversion dynamics. Using the integrated model, UC luminescence is maximized by adapting the Bragg stack design. For a Bragg stack of only 5 bilayers, UC luminescence is enhanced by a factor of 3.8 at an incident irradiance of 2000 W/m2. Our results identify the Bragg stack as promising for enhancing UC, especially in the low-irradiance regime, relevant for the application in photovoltaics. Therefore, we experimentally realized optimized Bragg stack designs. The PMMA layers, containing UC nanoparticles, are produced via spin-coating from a toluene based solution. The TiO2 layers are produced by atomic layer deposition from molecular precursors. The reflectance measurements show that the realized Bragg stacks are in good agreement with predictions from simulation.

Paper Details

Date Published: 18 April 2016
PDF: 9 pages
Proc. SPIE 9885, Photonic Crystal Materials and Devices XII, 98851A (18 April 2016); doi: 10.1117/12.2227121
Show Author Affiliations
C. L. M. Hofmann, Fraunhofer-Institut für Solare Energiesysteme (Germany)
Karlsruhe Institute of Technology (Germany)
S. Fischer, The Univ. of California, Berkeley (United States)
C. Reitz, Karlsruher Institut für Technologie (Germany)
B. S. Richards, Karlsruher Institut für Technologie (Germany)
J. C. Goldschmidt, Fraunhofer-Institut für Solare Energiesysteme (Germany)

Published in SPIE Proceedings Vol. 9885:
Photonic Crystal Materials and Devices XII
Dario Gerace; Gabriel Lozano; Christelle Monat; Sergei G. Romanov, Editor(s)

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