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Increased upconversion quantum yield in photonic structures due to local field enhancement and modification of the local density of states - a simulation-based analysis

: Herter, B.; Wolf, S.; Fischer, S.; Gutmann, J.; Bläsi, B.; Goldschmidt, J.C.

Postprint urn:nbn:de:0011-n-2643097 (2.5 MByte PDF)
MD5 Fingerprint: 2b7979eaa6539b4f247fc2a7057ef6fc
Created on: 31.1.2014

Optics Express 21 (2013), No.S5, pp.A883-A900
ISSN: 1094-4087
Journal Article, Electronic Publication
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Silicium-Photovoltaik; Farbstoff; Organische und Neuartige Solarzellen; Alternative Photovoltaik-Technologien; Herstellung und Analyse von hocheffizienten Solarzellen; Photonenmanagement; Neuartige Konzepte; Structures; Simulation; Upconversion; Waveguide

In upconversion processes, two or more low-energy photons are converted into one higher-energy photon. Besides other applications, upconversion has the potential to decrease sub-band-gap losses in silicon solar cells. Unfortunately, upconverting materials known today show quantum yields, which are too low for this application. In order to improve the upconversion quantum yield, two parameters can be tuned using photonic structures: first, the irradiance can be increased within the structure. This is beneficial, as upconversion is a non-linear process. Second, the rates of the radiative transitions between ionic states within the upconverter material can be altered due to a varied local density of photonic states. In this paper, we present a theoretical model of the impact of a photonic structure on upconversion and test this model in a simulation based analysis of the upconverter material -NaYF 4:20% Er3+ within a dielectric waveguide structure. The simulation combines a finite-difference time-domain simulation model that describes the variations of the irradiance and the change of the local density of photonic states within a photonic structure, with a rate equation model of the upconversion processes. We find that averaged over the investigated structure the upconversion luminescence is increased by a factor of 3.3, and the upconversion quantum yield can be improved in average by a factor of 1.8 compared to the case without the structure for an initial irradiance of 200 Wm-2.