Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 8: Joint Focussed Session: Thin Film Chalcogenide Photovoltaics I

HL 8.4: Topical Talk

Monday, March 14, 2011, 12:30–13:00, GER 37

Electrical Characterization of Cu(In,Ga)(Se,S)₂ -Based Solar Cells at Low Temperatures — •Udo Reislöhner — Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, Institut für Festkörperphysik, Max-Wien-Platz 1, D-07743 Jena, Germany

Thin-film solar cells based on Cu(In,Ga)(Se,S)₂-absorbers are industrially produced as mass product on a high level of quality. Due to rising production capacities and promising non-vacuum processes like chemical deposition or printing techniques a further cost reduction is expected. But contrary to the great success in production is the peculiar lack of comprehension concerning basic electrical spectroscopy of band-gap levels in this material system. A prominent example is the so called N1-defect observed by capacitance based methods like thermal admittance spectroscopy (TAS) and DLTS. It has unusual properties, e.g. a continuous shift of its band-gap level after moderate annealing, and has been controversially discussed for longer than a decade. However, these measurements extend to temperatures well below 200K and thereby overlap with the temperature domain where charge carrier transport by hopping is expected in the absorber. By consequently considering the impact of hopping transport on the capacitance measurement a hitherto undiscovered reason for a TAS-signal is found and the N1-signal is shown not to be correlated with a defect. Instead, this signal is generated by the freezing-out of carrier mobility with decreasing temperature when hopping conduction prevails. The consequence of this finding on electrical measurements and defect spectroscopy at Cu(In,Ga)(Se,S)₂-based solar cells will be discussed.