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KR: Fachverband Kristallographie

KR 6: Topical Session Photovoltaic Materials II (with MM and BV MatWerk)

KR 6.2: Vortrag

Mittwoch, 24. März 2010, 12:00–12:15, H4

Properties of grain boundaries in Cu(In,Ga)Se₂ and Cu(In,Ga)S₂ thin film solar cells deduced from mean inner coulomb potential measurements — •Sebastian S. Schmidt¹, Daniel Abou-Ras¹, Joachim Klaer¹, Raquel Caballero¹, Christoph T. Koch², Thomas Unold¹, and Hans-Werner Schock¹ — ¹Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany — ²Max Planck Institut für Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart, Germany

Polycrystalline Cu(In,Ga)Se₂ and Cu(In,Ga)S₂ thin films are efficient absorbers in thin film solar cells. The solar cell efficiencies strongly depend on the physical properties of grain boundaries in the absorbers. Here, we investigate the local behavior of the mean inner coulomb potential (MIP) at grain boundaries in Cu(In,Ga)Se₂ and Cu(In,Ga)S₂ solar cell absorbers. With in-line holography in a transmission electron microscope we measure MIP wells at grain boundaries in both types of absorber layers. The depth of the MIP wells depends on the grain boundary type as well as the composition. Generally, the potential wells have a FWHM of about 1 nm perpendicular to the plane of the grain boundary. Since the Debye length is about 10-40 nm in the absorber layers, considerable excess charge accumulations and related band bending at the analyzed grain boundaries can be excluded. A variation in composition seems to be responsible for the formation of MIP wells at grain boundaries. We discuss the local composition at grain boundaries by utilizing the isolated atom approximation.