Integration of IOH as a front contact layer for CIGS cells and modules
Darja Erfurt
*1
, Marc D. Heinemann
1
, Stefan Körner
2
, Bernd Szyszka
2
, Christian A.
Kaufmann
1
, Rutger Schlatmann
1
1
PVcomB - Helmholtz-Zentrum Berlin für Materialien und Energie, Schwarzschildstraße 3,
12489 Berlin, Germany
2
Technical University of Berlin, Department Technology of Thin Film Device TFD,
Einsteinufer 25, 10587 Berlin, Germany
* email:
Hydrogen doped indium oxide (IOH) is a promising transparent conductive oxide for opto-
electronic devices due to its remarkable high electron mobility and low light absorption in the
visible and infrared range [1]. As these films can be deposited at low temperatures they are
especially interesting for CIGS solar cells, replacing the commonly used ZnO:Al window
layer [2]. However, up to now, the theoretically possible current density increase of 2
mA/cm² hasn’t been shown yet for sputtered IOH films. In addition the necessary
crystallization of the initially amorphous layer has not been studied in real devices but on
isolated layers. In this work we show how the crystallization and the resulting electron
mobility of the IOH layers differ within the device compared to isolated layers. Especially the
method of the buffer layer deposition and its following treatments are shown to have a strong
influence. For this we focus our work on a Zn(O,S) buffer with and without an additional
intrinsic ZnO layer deposited with ALD and by magnetron sputtering.
Further, a deposition process on a large scale DC magnetron inline sputtering system is
developed. The process was scaled up to an area of up to 30x60 cm². Thereby we investigate
the incorporation of IOH not only for cells, but also for modules. The films were sputtered in
an Ar-O
2
atmosphere with additional water vapor, which is required to achieve an amorphous
growth of the indium oxide films. We show the post-deposition crystallization can be equally
optimized at different temperatures, durations and even in different atmospheres like vacuum
or air. Decisive factor here is the used water vapor pressure and the oxygen content during
the deposition step.
[1] T. Koida, H. Fujiwara und M. Kondo, „Hydrogen-doped In2O3 as High-mobility
Transparent Conductive Oxide“, Japanese Journal of Applied Physics Vol. 46 No. 28, pp.
685-687, 2007.
[2] T. Jäger, Y. E. Romanyuk, S. Nishiwaki, B. Bissig, F. Pianezzi, P. Fuchs, C. Gretener, M.
Döbeli und A. N. Tiwari, „Hydrogenated indium oxide window layers for high-efficiency
Cu(In,Ga)Se2 solar cells“, Journal of Applied Physics 117, 205301, 2015.
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