Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 8: Photovoltaics

HL 8.1: Talk

Monday, March 20, 2017, 09:30–09:45, POT 251

Light enhanced degradation of Cu(In,Ga)Se₂ investigated by time-resolved photo-luminescence and X-ray photoelectron spectroscopy — •Torsten Hölscher, Stefan Förster, Thomas Schneider, Setareh Zahedi-Azad, Eva Maria Zollner, Matthias Maiberg, and Roland Scheer — Martin-Luther-University Halle-Wittenberg, Germany

Cu(In,Ga)Se₂ (CIGSe) as absorber material for thin-film solar cells is known to degrade when exposed to air. So far, only little is known about the underlying surface processes. A method of choice for such an investigation is time-resolved photoluminescence (TRPL), which gives insight into the recombination kinetics of minority charge carriers. In our work, we have applied TRPL to CIGSe layers grown on molybdenum covered soda lime glass. The results show a strong decrease of the minority carrier lifetime after 10 till 60 min illumination with white light (1 sun) under ambient conditions. Measurement of X-ray photoelectron spectroscopy reveals an increase of the Na 1s and O 1s peak on the CIGSe surface. The position of the O 1s peak is centered at 531.7 eV, which we refer to the Na–O-CIGSe bonding complex. Based on TRPL and XPS we propose a light enhanced formation of this Na–O-CIGSe complex on the surface as the origin of the degradation. This model may also explain the often observed – "laser degradation" – during TRPL measurements. In the end, we discuss the influence of this degradation effect on the solar cell performance.