Physico-Chemical nanomaterials science

Single phase kesterite Cu2ZnSn(S,Se)4 thin films growth optimization for solar cell
Babichuk I.S.1,2, Golovynskyi S.1,2, Semenenko M.O.2, Datsenko O.I.3, Babichuk I.V.4, Qiu R.1, Xu G.1, Golovynska I.1, Li J.1, Li B.K.1, Qu J.L.1
1 Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, 518060, Shenzhen, P.R. China.
E-mail: ivan@szu.edu.cn
2 Institute of Semiconductor Physics, NAS of Ukraine, 03680, Kyiv, Ukraine.
3 Department of Physics, Taras Shevchenko National University of Kyiv, 01601, Kyiv, Ukraine.
4 National Center “Minor academy of sciences of Ukraine”, 04119, Kyiv, Ukraine.

Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) have attracted considerable attention as promising materials for new-generation of thin-ﬁlm solar cells. This work is aimed to optimize the growth parameters of kesterite thin films obtained by different methods including sulfurization of metallic layers, spray pyrolysis and flash deposition. The composition, morphology and microstructure of kesterite CZTS(Se) films with different thicknesses grown on glass substrates at various pressures and temperatures were studied on a submicron scale by Raman spectroscopy, EDS, X-ray diffraction, and SEM.
The lower sulfurization pressures have been shown to cause reduced disordering degree, however, higher pressures improved the crystallization and enlarged grain sizes, lowering the CZTS film porosity and, thus, the resistivity.
Study of the CZTS films grown by spray pyrolysis revealed that an increase in the substrate temperature and Cu content lead to a higher disorder of the crystal structure and to the formation of secondary phases, in particular, Cu2-xS. In turn, the secondary phase formation significantly affected the bandgap of CZTS. The substrate temperature near 290°C and Cu/Zn stoichiometric ratio of 2.0 were found to be the optimal growth parameters promoting the best crystal structure.
Studying the CZTSe “nanofilms” grown by flash deposition, a reduction of secondary phases and SnZn defect fraction were found with an increment in thickness. However, the share of disordered kesterite phase associated with CuZn defects was higher in thicker films. The thickness of ~200 nm was concluded as optimal.
The results can be useful for optimization of technological growth process.