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High-Efficient ZnO/PVD-CdS/Cu(In,Ga)Se2 Thin Film Solar Cells: Formation of the Buffer-Absorber Interface and Transport Properties

Published online by Cambridge University Press:  01 February 2011

Marin Rusu*
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Thilo Glatzel
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Christian A. Kaufmann
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Axel Neisser
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Susanne Siebentritt
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Sascha Sadewasser
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Thomas Schedel-Niedrig
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
Martha Ch. Lux-Steiner
Affiliation:
Hahn-Meitner-Institut Berlin, Department of Solar Energy, Glienickerstr. 100, 14109 Berlin, Germany
*
*corresponding author: rusu@hmi.de(M. Rusu)
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Abstract

For preparation of ZnO/CdS/Cu(In,Ga)Se2 solar cells, physical vapor deposition (PVD) was employed to deposit CdS buffer layers in ultrahigh vacuum on Se-decapped absorber surfaces, thus realizing an all ‘dry' fabrication process of the device. An 14.1% total area and 14.5% active area efficient ZnO/CdS/Cu(In,Ga)Se2 solar cell under AM1.5 conditions was achieved after annealing the as-prepared solar cells in air. Kelvin probe force microscopy (KPFM) measurements were carried out in-situ to monitor the initial growth of the CdS buffer layer on the absorber, as well as its electronic properties, in particular, the work function. It was observed that the PVD-CdS growth is initially inhibited at the absorber grain boundaries. Quantum efficiency measurements allowed us to suppose that during the initial growth stage a passivation of the grain boundaries occurs. The latter explains the higher short-circuit currents of the cells with PVD-CdS compared to their references with CdS grown by chemical bath deposition (CBD). The beneficial effect of the annealing seems to originate from a formation of a region with higher band gap than that of the absorber bulk and inverted conductivity type at the absorber surface, close to the CdS/Cu(In,Ga)Se2 interface, leading to a dramatic change in the electronic transport properties and finally, to a significant enhancement of the open-circuit voltage. Annealing of the ZnO/PVD-CdS/Cu(In,Ga)Se2 solar cells provides formation of PVDCdS/ Cu(In,Ga)Se2 interface with properties similar to that of reference samples with CBD-CdS.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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Footnotes

Graduate school of medicine and engineering, yamanashi university, 4-3-11 Takeda, Kofu city 400-8511 Japan

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