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Enhancement of photo-conversion efficiency in Cu2ZnSn(S,Se)4 thin-film
solar cells by control of ZnS precursor-layer thickness
Gee Yeong Kim1, Dae-Ho Son2, Trang Thi Thu Nguyen1, Seokhyun Yoon1, Minsu Kwon3, Chan-Wook Jeon3,
Dae-Hwan Kim2, Jin-Kyu Kang2,†, and William Jo1,*
1
Department of Physics and New and Renewable Energy Research Center, Ewha Womans University, Seoul, 120750, Korea
2
Advanced Convergence Research Center, Daegu Gyeongbuk Institute of Science and Technology, Daegu 711873, Korea
3
Department of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Korea
*Co-Corresponding author.
William Jo
(Tel.: +82 2 3277 4066; Fax: +82 2 32772372)
*E-mail address: wmjo@ewha.ac.kr
Jin-Kyu Kang
(Tel. +82-53-785-3700)
†
E-mail address: apollon@dgist.ac.kr
1. Secondary Ion Mass Spectrometry
Figure 1. SIMS depth profiles of the CZTSSe thin-film with different ZnS precursor thicknesses. (a)
330 (b) 337 (c) 344 nm-thick ZnS of the CZTSSe thin-films. The composition profiles of Zn and Sn in
the absorber layers are almost the same. There is an increase in the Na ratio towards the surface of (a)
and (b) of the CZTSSe thin-films.
2. Topography and Surface Potential measured by scanning probe microscopy
Figures 2–4 show the topography and the surface potential of the CZTSSe thin-films. (a)-(f) are
the topography and (g)-(l) are the surface potential images. We measured the surface potential value
of the CZTSSe thin-films by taking KPFM measurements with the depth profile. We obtained the
phase distribution based on a histogram of the work function. Thus, we can expect for the location
and the amount of the secondary phases of the CZTSSe thin-film with various ZnS precursor
thicknesses.
Figure 2. (a)-(f) Topography and (g)-(l) surface potential images of CZTSSe thin-films with
330 nm of ZnS precursor thickness.
Figure 3. (a)-(f) Topography and (g)-(l) surface potential images of CZTSSe thin-films with
337 nm of ZnS precursor thickness.
Figure 4. (a)-(f) Topography and (g)-(l) surface potential images of CZTSSe thin-films with
344 nm of ZnS precursor thickness.
3. Work function histogram of the CZTSSe thin-films with and without a DI-water etching
process
Figure 5 shows the work function histograms of the CZTSSe thin-film with and without
the DI-water etching process. (a) as-grown; (b) DI-water etched CZTSSe thin-films. The
CZTSe work function value remains unchanged. However, the CZTSSe work function
appears after the CZTSSe thin-films are etched with DI-water.
Figure 5. Work function histogram of (a) as-grown CZTSSe thin-film (b) DI-water etched
CZTSSe thin-film.
4. External quantum efficiency (EQE) of the same condition sample with the best cell of
CZTSSe. (typical EQE data)
Figure 6. EQE data of the same condition with 9.1% conversion efficiency of the CZTSSe
solar cell.