Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 5: Photovoltaics: CIGS and related compounds

HL 5.9: Vortrag

Montag, 16. März 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.