Kesterite [Cu2ZnSn(S,Se)4 (CZTSSe)], which is one of the most promising solar cell materials, can be used as a light absorber owing to its suitable optical and electrical properties. In this study, the optimization process of NaF layers was performed in the deposition of the precursor stacks of Sn/Cu/Zn/Mo to form CZTSSe thin films. The distribution of the secondary phases on the CZTSSe surfaces strongly depends on the insertion of the NaF layer. In particular, the Cu2-xS binary phase increases with the closeness of the insertion location of the NaF layer to the front side. Moreover, the grain boundary properties can be altered by varying the deposition conditions since Na segregation and defect formation affect the surface electrical properties and carrier transport mechanism. Photo-assisted conductive-atomic force microscopy was used to measure the local variation in the surface photocurrent flow into the CZTSSe grains, and the incorporation of sodium increased the surface current formation. This study exhibits the effects of Na on the optimal growth of kesterite formation and carrier transport of the relevant photovoltaic devices.
Bibliographical noteFunding Information:
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education ( NRF-2018R1A6A1A03025340 ) and Ministry of Science, Technology, ICT, and Future Planning ( NRF-2021R1A2B5B02001961 ). This work was supported by a grant ( NRF-2022M3J1A1064229 ) of the Technology Development Program for the solving of climate change, and these were provided through the National Research Foundation (NRF) funded by the Ministry of Science and ICT. This work was supported by the DGIST R&D programs of the Ministry of Science and ICT ( 22-CoE-ET-01 ). The first author, H. K. Park, is also grateful for the financial support received from the Hyundai Motor Chung Mong-Koo Foundation .
- Alkali doping control
- Charge transport
- Secondary phases