Review on Alkali Element Doping in Cu(In,Ga)Se<sub>2</sub> Thin Films and Solar Cells

Yun Sun; Shuping Lin; Wei Li; Shiqing Cheng; Yunxiang Zhang; Yiming Liu; Wei Liu

doi:10.1016/J.ENG.2017.04.020

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Engineering ›› 2017, Vol. 3 ›› Issue (4) : 452-459. DOI: 10.1016/J.ENG.2017.04.020

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Review on Alkali Element Doping in Cu(In,Ga)Se₂ Thin Films and Solar Cells

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Abstract

This paper reviews the development history of alkali element doping on Cu(In,Ga)Se₂ (CIGS) solar cells and summarizes important achievements that have been made in this field. The influences of incorporation strategies on CIGS absorbers and device performances are also reviewed. By analyzing CIGS surface structure and electronic property variation induced by alkali fluoride (NaF and KF) post-deposition treatment (PDT), we discuss and interpret the following issues: ① The delamination of CIGS thin films induced by Na incorporation facilitates CuInSe₂ formation and inhibits Ga during low-temperature co-evaporation processes. ② The mechanisms of carrier density increase due to defect passivation by Na at grain boundaries and the surface. ③ A thinner buffer layer improves the short-circuit current without open-circuit voltage loss. This is attributed not only to better buffer layer coverage in the early stage of the chemical bath deposition process, but also to higher donor defect ( $Cd Cu +$ ) density, which is transferred from the acceptor defect ( $V Cu −$ ) and strengthens the buried homojunction. ④ The KF-PDT-induced lower valence band maximum at the absorber surface reduces the recombination at the absorber/buffer interface, which improves the open-circuit voltage and the fill factor of solar cells.

Keywords

Alkali elements / Cu(In,Ga)Se₂ / Thin-film solar cells / Post-deposition treatment

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Yun Sun, Shuping Lin, Wei Li, Shiqing Cheng, Yunxiang Zhang, Yiming Liu, Wei Liu. Review on Alkali Element Doping in Cu(In,Ga)Se₂ Thin Films and Solar Cells. Engineering, 2017, 3(4): 452‒459 https://doi.org/10.1016/J.ENG.2017.04.020

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Acknowledgements

This work is supported by the YangFan Innovative & Entrepreneurial Research Team Project (2014YT02N037).

Compliance with ethics guidelines

Yun Sun, Shuping Lin, Wei Li, Shiqing Cheng, Yunxiang Zhang, Yiming Liu, and Wei Liu declare that they have no conflict of interest or financial conflicts to disclose.

RIGHTS & PERMISSIONS

2017 2017 THE AUTHORS. Published by Elsevier LTD on behalf of the Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).