Berlin 2012 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 38: Photovoltaics: CIGS and related Materials
HL 38.1: Talk
Tuesday, March 27, 2012, 11:15–11:30, ER 270
Characterization of grain boundaries in Cu(In,Ga)Se2 by atom probe tomography — •Torsten Schwarz1, Oana Cojocaru-Miredin1, Pyuck-Pa Choi1, Roland Würz2, and Dierk Raabe1 — 1Max-Planck Institute for Iron Research GmbH, Düsseldorf, Germany — 2Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Stuttgart, Germany
Solar cells based on the compound semiconductor Cu(In,Ga)Se2 (CIGS) as absorber material exhibit the highest efficiency among all thin-film solar cells. This is surprising high in view of the polycrystalline defect-rich structure of the CIGS absorber films. The high efficiency has been commonly ascribed to the diffusion of alkali metal atoms from the soda-lime glass substrate into the CIGS layer, which can render the grain boundaries (GB) electrally inactive.
However, the exact mechanisms of how these impurities enhance the cell efficiency are yet to be clarified.
As a step towards a better understanding of CIGS solar cells, we have analyzed the composition of solar-grade CIGS layers at the atomic-scale by using pulsed laser Atom Probe Tomography (APT). To perform APT analyses on selected GBs site-specific sample preparation was carried out using the Focused Ion Beam lift-out technique. In addition, Electron Back Scattered Diffraction was performed to characterize the structure and misorientation of selected GBs.
Using APT, segregation of impurities at the GBs was directly observed. APT data of various types of GBs will be presented and discussed with respect to the possible effects on the cell efficiency.