Dresden 2011 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 23: Joint Focussed Session: Thin Film Chalcogenide Photovoltaics II

HL 23.3: 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 Boit¹ — ¹Department 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.