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Study of the semiconducting properties of Cu2ZnSnS4 thin films grown by ultrasonic spray pyrolysis of waterdissolved precursors Ignacio Estevez Espinoza1,* , Yasuhiro Matsumoto Kuwabara1,2, Mauricio Ortega Lo´pez1,2, and J. Octavio Estevez Espinoza3 1

Doctoral Program of Nanoscience and Nanotechnology, CINVESTAV-IPN, Avenida IPN No 2508, 07360 México City, México Electrical Engineering Department (SEES) CINVESTAV-IPN, Avenida IPN No 2508, 07360 México City, México 3 Instituto de Física UNAM, Circuito de la Investigación Científica, Ciudad Universitaria Delegación Coyoacán, C.P. 02376 México City, México 2

Received: 21 October 2019

ABSTRACT

Accepted: 7 October 2020

Cu2ZnSnS4 (CZTS) thin films were deposited on glass-slide substrates by ultrasonic spray pyrolysis at the substrate temperatures in the 330–420 °C range, using water–ethanol solutions containing CuCl2–H2O, ZnCl2, SnCl2, and (NH2)2CS (thiourea). After being deposited, CZTS films were annealed under vacuum and then characterized in regarding their structural and optical properties. The X-ray diffraction and Raman spectroscopy studies indicated that CZTS thin films with kesterite as predominant phase could be obtained. The X-ray diffraction patterns of all deposited samples displayed diffraction peaks corresponding to the planes (112), (220), and (312) of kesterite CZTS and diffraction peaks belonging to phases other than CZTS were apparently undetectable for the X-ray technique. Furthermore, their Raman spectra were featured for a widely structured Raman band in the 200–400 cm-1 wavenumber area. After being deconvoluted, Raman peaks belonging only to kesterite CZTS were revealed. However, a further analysis of the UV–Vis absorbance spectra indicated all our films strongly absorbs in this spectral region. In the low photon energy region (\ 1.5 eV), Tauc plots revealed electron transitions with characteristic energy values in the 1.15–1.34 eV range, which could be attributed at the presence of tetragonal Cu2SnS3 and point defects (VS and VZn) into CZTS. All prepared CZTS films display the p-type conductivity as verified by Hall measurements.

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Springer Science+Business

Media, LLC, part of Springer Nature 2020

Address correspondence to E-mail: [email protected]; [email protected]

https://doi.org/10.1007/s10854-020-04622-x

J Mater Sci: Mater Electron

1 Introduction Cu2ZnSnS4 (CZTS) is currently studied due to its suitable photovoltaics properties as the p-type absorber material of highly efficient thin-film solar cells. Besides, it holds promise to reduce the cost of thin-film solar cells because its elements are nontoxic, cheap, and abundant in the earth crust. The kesterite phase of CZTS has a direct energy gap of 1.4–1.6 eV, and an absorption coefficient over 104 cm-1 in its strong absorption region [1]. Several studies on the CZTS synthesis by various methods have reported that the formation of CZTS involves the admixing of binary sulfides, Cu2S, ZnS, and SnS2 [2–5]. As suggested for the pseudo-ternary phase diagram Cu2S-ZnS-SnS2