Berlin 2015 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 5: Photovoltaics: CIGS and related compounds
HL 5.9: Talk
Monday, March 16, 2015, 11:30–11:45, EW 202
Simulation of interference-related lineshape distortions in electroreflectance spectra of Cu(In,Ga)Se2 thin-film solar cells — •Christian Huber1, Christoph Krämmer1, David Sperber1, Heinz Kalt1, Michael Powalla2, and Michael Hetterich1 — 1Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany — 2Light Technology Institute, KIT and Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, 70565 Stuttgart, Germany
Modulation spectroscopy techniques like electroreflectance (ER) have proven to be powerful methods to determine the energetic positions of critical points (CPs) in a semiconductor’s band structure. In the low-field regime the sharp, derivative-like features at the CPs can easily be evaluated by fitting a third-derivative functional form (TDFF) lineshape to the measured spectra.
However, when applied to thin-film solar cells to determine the absorber band gap, deviations from the TDFF approach have to be considered. One important aspect is that the layer stack of the solar cell introduces layer thickness interferences in the reflection signal, which can strongly distort the ER spectra.
In this contribution a transfer matrix approach will be presented in order to model the ER spectra of Cu(In,Ga)Se2 thin-film solar cells. It shows that interference effects introduce lineshape distortions whenever interference minima lie energetically close to a CP. These distortions can easily be misinterpreted as contributions from several CPs and will therefore lead to wrong results in a TDFF-evaluation.