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HL: Fachverband Halbleiterphysik

HL 5: Photovoltaic

HL 5.9: Vortrag

Montag, 23. März 2009, 12:45–13:00, POT 151

Diffusion of substrate impurities into solar-grade CIGS layer structures — •Shahmahmood Obeidi¹, Roland Würz², Axel Eicke², and Nicolaas Stolwijk¹ — ¹Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany — ²Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, Industriestr. 6, 70565 Stuttgart, Germany

The deposition of CIGS involves the diffusion of impurities out of the substrate through the Mo back contact into the absorber layer of the solar cell. In some cases, e.g., Fe the performance of the cell is found to suffer. Therefore it is important to study the diffusion behaviour of such impurities both qualitatively and quantitatively. We investigated the diffusion of iron in polycrystalline CIGS after growth. In order to start with Fe-free CIGS layers before the diffusion experiment we chose CIGS/Mo/float-glass structures as samples and provided them with front-side Fe sources. Two methods were applied: the radiotracer method using Fe-59 as suitable isotope and secondary ion mass spectrometry (SIMS) with natural Fe as diffusion source. Diffusion anneals in the temperature range from 200^∘C to 500^∘C were performed in a lamp furnace or an oil bath. The values for the diffusion coefficient range from 7.5·10⁻¹⁵ to 8.8·10⁻¹² cm²s⁻¹ in the temperature interval investigated. An activation enthalpy of 1.0 eV was determined from an Arrhenius fit and the extrapolation of the Arrhenius line to the CIGS deposition temperature (550^∘C) yields a diffusion coefficient of 2.0·10⁻¹⁰ cm²s⁻¹. We will discuss to what extent the present results may be interpreted in terms of grain boundary diffusion.