Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 6: Photovoltaics I

HL 6.2: Talk

Monday, March 12, 2018, 09:45–10:00, EW 203

The beneficial effect of Rubidium in Cu(In,Ga)Se₂ solar cells — •Philipp Schöppe¹, Sven Schönherr¹, Roland Wuerz², Wolfgang Wisniewski³, Gema Martínez-Criado^4,5, Maurizio Ritzer¹, Konrad Ritter¹, Carsten Ronning¹, and Claudia Sarah Schnohr¹ — ¹Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Germany — ²Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, Stuttgart, Germany — ³Otto-Schott-Institut, Friedrich-Schiller-Universität Jena, Germany — ⁴Instituto de Ciencia de Materiales de Madrid, Spain — ⁵European Synchrotron Radiation Facility, Grenoble, France

Cu(In,Ga)Se₂ solar cells are the most efficient ones among all thin film photovoltaics. The current world record efficiency was realized by applying a RbF post deposition treatment (PDT) to the absorber. However, it is not clear why the introduced Rb improves the solar cell performance. In order to investigate the beneficial effect of Rb, a Cu(In,Ga)Se₂ absorber was grown on a Mo coated alkali free substrate and subjected to a RbF PDT. This pure RbF PDT leads to a significantly higher efficiency. A thin cross sectional lamella was cut out of the layer stack and investigated via a combination of electron microscopy and synchrotron based x-ray fluorescence analysis. This approach provides clear indications of the origin of the beneficial effect of Rb. It is evident that Rb segregates at random grain boundaries and dislocation cores, where it likely passivates defects. In contrast, Rb does not segregate at Σ3 twin boundaries. Additionally, Rb agglomerates at the interface between the absorber and the MoSe₂ layer.