Investigating Structural and Optical Properties of CZTS Thin Films through Ag and Ge Alloying

Mehmet Ali Olğar; Recep Zan; Ali Çiriş; Yavuz Atasoy

doi:10.5281/zenodo.8007885

Authors

Mehmet Ali Olğar Niğde Ömer Halisdemir University, Faculty of Arts and Sciences, Department of Physics, 51240, Niğde, Türkiye https://orcid.org/0000-0002-6359-8316
Recep Zan Niğde Ömer Halisdemir University, Faculty of Arts and Sciences, Department of Physics, 51240, Niğde, Türkiye https://orcid.org/0000-0001-6739-4348
Ali Çiriş Niğde Ömer Halisdemir University, Nanotechnology Application and Research Center, 51240, Niğde, Türkiye https://orcid.org/0000-0003-4266-2080
Yavuz Atasoy Niğde Ömer Halisdemir University, Niğde Zübeyde Hanım Vocational School of Health Services, 51240, Niğde, Türkiye https://orcid.org/0000-0002-6382-992X

DOI:

https://doi.org/10.5281/zenodo.8007885

Keywords:

CZTS, Ag-CZTS, Ge-CZTS, Sputtering, Thin film

Abstract

In this study, the effect of Ag and Ge doping on the structural and optical properties of CZTS thin films was investigated. Undoped, Ag-doped, and Ge-doped CZTS samples were fabricated by two-step process involving sputter deposition of precursor films on the Mo-coated glass substrates and the sulfurization process of these films by Rapid Thermal Annealing (RTA) method. Prepared samples were characterized through several methods. EDX measurements revealed that all samples had Cu-poor and Zn-rich chemical composition regardless of the dopant materials. Furthermore, Ag and Ge concentrations were found to be 4% and 13%, respectively. XRD spectra of CZTS samples revealed only diffraction peaks of the kesterite CZTS phase. It was observed in extended XRD graphs that there was a slight shift in the diffraction peaks of doped CZTS samples due to incorporating Ag and Ge in the host lattice, as expected. Raman spectra of the films confirmed the formation of kesterite CZTS phase. In addition, it was seen that the formation of CTS phase was prevented by doping of CZTS thin films through Ag and Ge dopant materials. The optical band gap of CZTS, Ge-CZTS, and Ag-CZTS thin films was found as 1.50, 1.52 and 1.55 eV, respectively. Overall, it was demonstrated that Ag and Ge doping was performed successfully and prevented the formation of a secondary phase, which has an adverse effect on potential solar cell performance.

References

Nakamura, M., Yamaguchi, K., Kimoto, Y., Yasaki, Y., Kato, T., and Sugimoto, H. "Cd-Free Cu(In,Ga)(Se,S)2 Thin-Film Solar Cell With Record Efficiency of 23.35%", IEEE Journal of Photovoltaics 9 (6) 1863-1867 (2019).

Green, M.A., Dunlop, E.D., Siefer, G., Yoshita, M., Kopidakis, N., Bothe, K., and Hao, X.J. "Solar cell efficiency tables (Version 61)", Progress in Photovoltaics 31 (1) 3-16 (2023).

Olgar, M.A., Seyhan, A., Sarp, A.O., and Zan, R. "Impact of sulfurization parameters on properties of CZTS thin films grown using quaternary target", Journal of Materials Science: Materials in Electronics 31 (22) 20620-20631 (2020).

Jimbo, K., Kimura, R., Kamimura, T., Yamada, S., Maw, W.S., Araki, H., Oishi, K., and Katagiri, H. "Cu2ZnSnS4-type thin film solar cells using abundant materials", Thin Solid Films 515 (15) 5997-5999 (2007).

Shockley, W. and Queisser, H.J. "Detailed Balance Limit of Efficiency of p‐n Junction Solar Cells", Journal of Applied Physics 32 (3) 510-519 (1961).

Gong, Y., Zhang, Y., Zhu, Q., Zhou, Y., Qiu, R., Niu, C., Yan, W., Huang, W., and Xin, H. "Identifying the origin of the V oc deficit of kesterite solar cells from the two grain growth mechanisms induced by Sn 2+ and Sn 4+ precursors in DMSO solution", Energy & Environmental Science 14 (4) 2369-2380 (2021).

Atasoy, Y. "Effect of annealing temperature on the microstructural and optical properties of newly developed (Ag, Cu) 2Zn (Sn, Ge) Se4 thin films", Applied Physics A 128 (11) 1030 (2022).

Hages, C.J., Koeper, M.J., and Agrawal, R. "Optoelectronic and material properties of nanocrystal-based CZTSe absorbers with Ag-alloying", Solar Energy Materials and Solar Cells 145 342-348 (2016).

Chen, S., Walsh, A., Gong, X.G., and Wei, S.H. "Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers", Adv Mater 25 (11) 1522-39 (2013).

Denton, A.R. and Ashcroft, N.W. "Vegard’s law", Physical review A 43 (6) 3161 (1991).

Cui, H., Liu, X., Liu, F., Hao, X., Song, N., and Yan, C. "Boosting Cu2ZnSnS4 solar cells efficiency by a thin Ag intermediate layer between absorber and back contact", Applied Physics Letters 104 (4) 041115 (2014).

Saini, N., Larsen, J.K., Sopiha, K.V., Keller, J., Ross, N., and Platzer-Björkman, C. "Germanium incorporation in Cu2ZnSnS4 and formation of a Sn–Ge gradient", physica status solidi (a) 216 (22) 1900492 (2019).

Olgar, M.A., Başol, B.M., Tomakin, M., and Bacaksız, E. "Phase transformation in Cu2SnS3 (CTS) thin films through pre-treatment in sulfur atmosphere", Journal of Materials Science: Materials in Electronics 32 (8) 10018-10027 (2021).

Altamura, G. and Vidal, J. "Impact of minor phases on the performances of CZTSSe thin-film solar cells", Chemistry of Materials 28 (11) 3540-3563 (2016).

Tauc, J. "Optical properties and electronic structure of amorphous Ge and Si", Materials Research Bulletin 3 (1) 37-46 (1968).

Yang, S., Wang, S., Liao, H., Xu, X., Tang, Z., Li, X., Wang, T., Li, X., and Liu, D. "The impact of different Ag/(Ag+ Cu) ratios on the properties of (Cu 1− x Ag x) 2 ZnSnS 4 thin films", Journal of Materials Science: Materials in Electronics 30 11171-11180 (2019).

Sanchez, T., Regalado-Pérez, E., Mathew, X., Sanchez, M., Sanchez, Y., Saucedo, E., and Mathews, N. "Ge doped Cu2ZnSnS4: An investigation on absorber recrystallization and opto-electronic properties of solar cell", Solar Energy Materials and Solar Cells 198 44-52 (2019).

Olgar, M., Sarp, A., Seyhan, A., and Zan, R. "Impact of stacking order and annealing temperature on properties of CZTS thin films and solar cell performance", Renewable Energy 179 1865-1874 (2021).