Dresden 2011 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 39: Photovoltaics: Chalcopyrites I

HL 39.4: Vortrag

Dienstag, 15. März 2011, 14:15–14:30, FOE Anorg

Impact of thickness reduction of the ZnO:Al window layer on opto-electronical properties of CIGSSe solar cells — •Jan Keller¹, M. Knipper¹, J. Parisi¹, I. Riedel¹, T. Dalibor², and A. Avellan² — ¹Thin Film Photovoltaics, University of Oldenburg, D-26111 Oldenburg — ²AVANCIS GmbH & Co. KG, D-81739 Munich

The application of highly doped transparent conducting oxides in chalcopyrite solar cells requires an optimized trade-off between optical transmission and sheet-conductivity. In this respect we studied the thickness variation of ZnO:Al films used as window layer in Cu(In,Ga)(Se,S)₂ (CIGSSe) thin film solar cells. Thin ZnO:Al layers (200nm) on glass exhibit significantly enhanced transmission at wavelengths λ<400nm while a considerable sub-bandgap absorption at λ>800nm appears in thicker films which is attributed to free charge carrier absorption. The IV-characteristics of CIGSSe solar cells with d_ZnO:Al=200nm exhibit a strong enhancement of the short-circuit current density J_SC (Δ J_SC=3mA) as compared to samples with conventional ZnO:Al-film thickness. However, the reduced parallel (R_p) and increased series (R_s) resistance of samples with thin ZnO:Al-layer cause reduction of the fill factor, which has direct consequences for the series connection of cells in a CIGSSe-module. XRD-diffractograms suggest that the high R_s in thin ZnO:Al is not only related to the thickness but also due to reduced (002)-texture that appears to be beneficial for lateral conductivity. By thermographic investigations we are able to directly locate the cell-regimes responsible for the decreased R_p.