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Dresden 2011 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 5: Thin Film Chalcogenide Photovoltaics II (Focused Session -- Organiser: Ronning)

DS 5.3: Vortrag

Montag, 14. März 2011, 15:30–15:45, GER 37

Investigation of lattice defects and compositional gradients in Cu(In,Ga)Se2 thin films for solar cells — •Jens Dietrich1, Daniel Abou-Ras2, Thorsten Rissom2, Thomas Unold2, Hans-Werner Schock2, and Christian Boit11Department of Semiconductor Devices, Berlin University of Technology, Einsteinufer 19, 10587 Berlin — 2Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin

Cu(In,Ga)Se2 absorber layers used in thin-film solar cells exhibit, when grown in a multi-stage process, compositional gradients of gallium and indium, dependent on process parameters such as the Ga content. The high lateral resolution of transmission electron microscopy (TEM) imaging and energy-dispersive X-ray spectroscopy (EDX) allows the determination of lattice defects and the elemental concentrations at identical sample positions. Cross-sectional TEM samples of ZnO/CdS/Cu(In,Ga)Se2/Mo/glass stacks were prepared with varying [Ga]/([In]+[Ga]) ratio in the absorber. The shape of the Ga distribution was measured by means of EDX and differs for the various [Ga]/([In]+[Ga]) ratios. Linear (dislocations) and planar defects (stacking faults, microtwins) were studied by means of TEM bright field and dark field images along the lengths of the Cu(In,Ga)Se2 layers. Strong Ga compositional gradients were found even within individual grains. It appears that these Ga gradients correlate with the occurrence of dislocation networks in large grains (diameter > 1 µm). We assume that these dislocations compensate for lattice mismatch due to the change in composition in this area of the lattice.

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