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Trivalent rare-earth ions as photon down-shifter for photovoltaic applications

: Steudel, F.; Loos, S.; Ahrens, B.; Schweizer, S.


Wehrspohn, R.B. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Photonics for Solar Energy Systems V : Brussels, Belgium, 14.04.2014-16.04.2014
Bellingham, WA: SPIE, 2014 (Proceedings of SPIE 9140)
ISBN: 978-1-628-41088-4
Paper 91400I, 7 S.
Conference "Photonics for Solar Energy Systems" <5, 2014, Brussels>
Fraunhofer IWM ()

Rare-earth doped borate glasses are investigated for their potential as photon down-shifting cover glass for CdTe solar cells. Note, that CdTe solar cells have a poor response in the ultraviolet and blue spectral range due to absorption in the CdS buffer layer having a band gap of 2.4 eV. The following trivalent rare-earth ions are analyzed in detail: Sm3+, Eu 3+, and Tb3+. These ions provide strong absorption bands in the ultraviolet / blue spectral range and an intense emission in the red (Sm3+ and Eu3+) or green (Tb3+) spectral range. The gain in short-circuit current density of a CdTe solar cell is calculated for different rare-earth ion concentrations. The calculations are based on the rare-earth's absorption coefficients as well as their photoluminescence (PL) quantum efficiency. For Sm3+, the PL quantum efficiency depends significantly on the doping concentration. Finally, the potential of double-doped borate glasses, i.e. glasses doped with two different rare-earth ions, is investigated.