Berlin 2012 – scientific programme

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DS: Fachverband Dünne Schichten

DS 5: Thin film photovoltaics: CIGSe + CdTe

DS 5.2: Talk

Monday, March 26, 2012, 10:15–10:30, H 2032

Strongly Confined and Chemically Flexible Grain Boundaries in Cu(In,Ga)Se₂ Thin Films — Daniel Abou-Ras¹, Sebastian S. Schmidt¹, •Raquel Caballero^1,2, Thomas Unold¹, Hans-Werner Schock¹, Christoph T. Koch³, Bernhard Schaffer⁴, Miroslava Schaffer⁴, Oana Cojocaru-Mirédin⁵, and Pyuck-Pa Choi⁵ — ¹HZB, Berlin, Germany — ²UAM, Madrid, Spain — ³Ulm University, Germany — ⁴SuperSTEM, UK — ⁵MPI for Iron Research, Düsseldorf, Germany

In the present work, we will show by means of electron holography, EFTEM and APT with spatial resolutions in the subnanometer range that substantial changes in composition with respect to the grain interiors are found at GBs in Cu(In,Ga)Se₂ (CIGSe) thin films within only about 1 nm wide regions. At Se-cation terminated twin boundaries, Cu depletion was measured, whereas considerable In enrichment and Cu depletion are visible in EFTEM maps of the Se/Se-terminated twins. At random GBs, Cu enrichment and In depletion as well as Cu depletion and In enrichment were found. Often, also enhanced Na, O, and K signals are detected at random GBs. Although no general compositional change at random CIGSe GBs was identified , the trends in Cu and In concentrations were always anticorrelated. These results suggest mechanisms of atomic/ionic redistribution at twin boundaries and random GBs, occurring within regions confined to only about 1 nm in width around the GBs, being also influenced by the trace elements segregated to the GBs. The apparent anticorrelation of Cu and In signals suggests a preferential site exchange of Cu and In atoms.