The effect of different Zn salt precursors on solar cell device performance is investigated using low band Cu(In,Ga)(S,Se)2 (CIGSSe) and large band gap CuInS2 (CIS) absorbers provided by AVANCIS and SULFURCELL Solartechnik respectively. The deposition of a Zn(S,O) layer by chemical bath deposition (CBD) process is described. This process has been successfully developed for the deposition of Zn(S,O) buffer layers on laboratory scale samples using CIS absorbers from the technology department (SE3) at the Hahn-Meitner-Institut [1,2] and is currently being up-scaled to substrates up to 30cm x 30cm. During the first minutes of the process the solution stays relatively clear. After some time, which depends on the CBD conditions, there is an increase of the turbidity probably due to the formation of Zn(OH)₂. This turbidity has been monitored using an optical setup. Light from a laser source is scattered by the particles formed in the solution. The transmitted light is detected at a Si-sensor and plotted vs. time. Transmission electron micrographs of glass/Mo/CIS/Zn(S,O) structures show a conformal coverage of the absorber by a Zn(S,O) layer of 15-25 nm consisting of nanocrystals with radii of ~5 nm. Scanning electron micrographs (SEM) reveal different crystal structures depending on the zinc precursor used and on the temperature of the CBD.
The results for small area (0.5 cm²) single cells as well as large area modules (10x10 cm² and 30x30 cm²) with interconnected cells are also discussed. The new process shows similar results compared to CdS base line and can be successful in an industrial pilot line.

[1] German Patent. International Publication Number: WO 2006/0180013 A1
[2] A. Ennaoui , M. Bär, J. Klaer, T. Kropp, R. Sáez-Araoz and M. Ch. Lux-Steiner
Highly-efficient Cd-free CuInS₂ Thin-film Solar Cells and Mini-modules with Zn(S,O) Buffer Layers Prepared by an Alternative Chemical Bath Process
Prog. Photovolt: Res. Appl. 2006; 14:499–511

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1. Study of CIS based solar cells with a ALCVD ZnO/ZnO:Al as window layers
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