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Diffusion Behavior and Microstructural Properties of the CBD-ZnS/CIGS Interface Boundary

Published online by Cambridge University Press:  21 March 2011

Tokio Nakada
Tokio Nakada*
Affiliation:
Department of Electrical Engineering and electronics, Aoyama Gakuin University Setagaya-ku, Tokyo 157-8572, Japan
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Abstract

The diffusion behavior and microstructural properties of the CBD-ZnS/Cu(In,Ga)Se2 (CIGS) interface of high-efficiency Cd-free CIGS thin film solar cells with efficiencies exceeding 17 % have been investigated using energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). CBD-ZnS thin layers are found to grow with small polycrystalline grains that consist of sphalerite and wurtzite phases. This is in sharp contrast to CBD-CdS layers which grow epitaxially on CIGS grains. Micro-EDX analysis revealed Zn indiffusion into the CIGS thin layer a distance of approximately 40 nm from the CBD-ZnS/CIGS interface boundary after air-annealing at 200°C, whereas no diffusion of Zn was observed before annealing. These results suggest that the main role of the air-annealing process is not substitution of Se vacancies by oxygen atoms but the diffusion of Zn into CIGS which may result in the formation of a pn homojunction. On the other hand, negligible Zn-diffusion into a CuGaSe2 thin film was found at the CBD-ZnS/CuGaSe2 interface boundary even after air-annealing. The cell performance of CBD-ZnS/CIGS thin film solar cells is discussed in connection with the Ga/(In+Ga) atomic ratio, conduction band-offset and Zn-diffusion.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 668: Symposium H – II-IV Compound Semiconductor Photovoltaic Materials , 2001 , H7.1
Copyright
Copyright © Materials Research Society 2001

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References

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